Define case and conduct case finding Dr. Christina Rundi Ministry of Health, Malaysia Foodborne Outbreak Investigation, Hanoi, 1-5 June 2009
Define case and conduct case finding Dr. Christina Rundi Ministry of Health, Malaysia Foodborne Outbreak Investigation, Hanoi, 1-5 June 2009.
Dec 14, 2015
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Define case and conduct case finding
Dr Christina RundiMinistry of Health Malaysia
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Introduction
bull Careful description and characterization of the outbreak is an important first step in any epidemiological investigation
bull Descriptive epidemiology provides a picture of the outbreak in terms of the three standard epidemiological parameters ndash time place and
person
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
What is case definition
bull A set of criteria to determine whether a person should be classified as being affected by the disease under investigation
bull It is an epidemiological tool for counting cases not used to guide clinical practice
bull A case definition should be simple and practical
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Components of Case Definition
bull FOUR components
clinical and laboratory criteria the clinical features should be significant or hallmark signs of the illness
a defined period of time
restriction by ldquoplacerdquorestriction by ldquopersonrdquo characteristics ndash limiting the
group to for example persons over one year of age persons with no recent diarrhoeal disease etc
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Common components and examples of an outbreak case definition
Element Descriptive features Examples Person Age group ldquochildren under the age of 5 yearsrdquo
Sex ldquomalesrdquo Occupation ldquohealth care workers at hospital Xrdquo RaceExclusion criteria ldquopersons with no previous history of
chronic cough or asthmardquo Place Geographic location ldquoresident of Y county or staterdquo
Facility ldquoliving in X nursing homerdquo ldquostudent at A high schoolrdquo
Time Illness onset ldquoonset of illness between May 4 and August 31 2007rdquo
Clinical features Pneumonia ldquoclinical or radiographically confirmed pneumoniardquo ldquoshortness of breath and feverrdquo
Laboratory Cultures serology Pneumococcus isolated criteria from blood rapid influenza test
positive Foodborne Outbreak Investigation Hanoi
1-5 June 2009
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Introduction
bull Careful description and characterization of the outbreak is an important first step in any epidemiological investigation
bull Descriptive epidemiology provides a picture of the outbreak in terms of the three standard epidemiological parameters ndash time place and
person
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
What is case definition
bull A set of criteria to determine whether a person should be classified as being affected by the disease under investigation
bull It is an epidemiological tool for counting cases not used to guide clinical practice
bull A case definition should be simple and practical
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Components of Case Definition
bull FOUR components
clinical and laboratory criteria the clinical features should be significant or hallmark signs of the illness
a defined period of time
restriction by ldquoplacerdquorestriction by ldquopersonrdquo characteristics ndash limiting the
group to for example persons over one year of age persons with no recent diarrhoeal disease etc
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Common components and examples of an outbreak case definition
Element Descriptive features Examples Person Age group ldquochildren under the age of 5 yearsrdquo
Sex ldquomalesrdquo Occupation ldquohealth care workers at hospital Xrdquo RaceExclusion criteria ldquopersons with no previous history of
chronic cough or asthmardquo Place Geographic location ldquoresident of Y county or staterdquo
Facility ldquoliving in X nursing homerdquo ldquostudent at A high schoolrdquo
Time Illness onset ldquoonset of illness between May 4 and August 31 2007rdquo
Clinical features Pneumonia ldquoclinical or radiographically confirmed pneumoniardquo ldquoshortness of breath and feverrdquo
Laboratory Cultures serology Pneumococcus isolated criteria from blood rapid influenza test
positive Foodborne Outbreak Investigation Hanoi
1-5 June 2009
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
What is case definition
bull A set of criteria to determine whether a person should be classified as being affected by the disease under investigation
bull It is an epidemiological tool for counting cases not used to guide clinical practice
bull A case definition should be simple and practical
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Components of Case Definition
bull FOUR components
clinical and laboratory criteria the clinical features should be significant or hallmark signs of the illness
a defined period of time
restriction by ldquoplacerdquorestriction by ldquopersonrdquo characteristics ndash limiting the
group to for example persons over one year of age persons with no recent diarrhoeal disease etc
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Common components and examples of an outbreak case definition
Element Descriptive features Examples Person Age group ldquochildren under the age of 5 yearsrdquo
Sex ldquomalesrdquo Occupation ldquohealth care workers at hospital Xrdquo RaceExclusion criteria ldquopersons with no previous history of
chronic cough or asthmardquo Place Geographic location ldquoresident of Y county or staterdquo
Facility ldquoliving in X nursing homerdquo ldquostudent at A high schoolrdquo
Time Illness onset ldquoonset of illness between May 4 and August 31 2007rdquo
Clinical features Pneumonia ldquoclinical or radiographically confirmed pneumoniardquo ldquoshortness of breath and feverrdquo
Laboratory Cultures serology Pneumococcus isolated criteria from blood rapid influenza test
positive Foodborne Outbreak Investigation Hanoi
1-5 June 2009
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Components of Case Definition
bull FOUR components
clinical and laboratory criteria the clinical features should be significant or hallmark signs of the illness
a defined period of time
restriction by ldquoplacerdquorestriction by ldquopersonrdquo characteristics ndash limiting the
group to for example persons over one year of age persons with no recent diarrhoeal disease etc
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Common components and examples of an outbreak case definition
Element Descriptive features Examples Person Age group ldquochildren under the age of 5 yearsrdquo
Sex ldquomalesrdquo Occupation ldquohealth care workers at hospital Xrdquo RaceExclusion criteria ldquopersons with no previous history of
chronic cough or asthmardquo Place Geographic location ldquoresident of Y county or staterdquo
Facility ldquoliving in X nursing homerdquo ldquostudent at A high schoolrdquo
Time Illness onset ldquoonset of illness between May 4 and August 31 2007rdquo
Clinical features Pneumonia ldquoclinical or radiographically confirmed pneumoniardquo ldquoshortness of breath and feverrdquo
Laboratory Cultures serology Pneumococcus isolated criteria from blood rapid influenza test
positive Foodborne Outbreak Investigation Hanoi
1-5 June 2009
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Common components and examples of an outbreak case definition
Element Descriptive features Examples Person Age group ldquochildren under the age of 5 yearsrdquo
Sex ldquomalesrdquo Occupation ldquohealth care workers at hospital Xrdquo RaceExclusion criteria ldquopersons with no previous history of
chronic cough or asthmardquo Place Geographic location ldquoresident of Y county or staterdquo
Facility ldquoliving in X nursing homerdquo ldquostudent at A high schoolrdquo
Time Illness onset ldquoonset of illness between May 4 and August 31 2007rdquo
Clinical features Pneumonia ldquoclinical or radiographically confirmed pneumoniardquo ldquoshortness of breath and feverrdquo
Laboratory Cultures serology Pneumococcus isolated criteria from blood rapid influenza test
positive Foodborne Outbreak Investigation Hanoi
1-5 June 2009
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Examples of a case definition bull Student attending X High School who has onset of fever and
cough between January 4 and 24 2007
bull ldquoA resident of or visitor to Rapid City South Dakota who was diagnosed by a physician either clinically or radiographically with community-acquired pneumonia (CAP) with symptom onset after May 1 2005 and who had laboratory confirmation of Legionnairesrsquo disease by culture of Legionella by urinary antigen test for Legionella pneumophila serogroup 1 (Lp1) by a four-fold or greater rise in serum antibody titer to Lp1 or detection of specific Legionella antigen by direct fluorescent antibody stainingrdquo
Gregg MB Field Epidemiology New York Oxford University Press 2002
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Concept of Sensitivity and Specificitybull The sensitivity measures the proportion of actual positives
which are correctly identified bull Example the percentage of sick people who are identified as
having the conditionbull The specificity measures the proportion of negatives which
are correctly identified bull Example the percentage of well
people who are identified as not having the condition
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Sensitivity and specificity
bull Ideally a case definition will include all cases (high sensitivity) but exclude any person who does not have the illness (high specificity)
bull A sensitive case definition will detect many cases but may also count as cases individuals who do not have the disease
bull A more specific case definition is more likely to include only persons who truly have the disease under investigation but also more likely to miss some cases
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
How to develop a Case Definition
Measles possible case definitions
bull Fever and runny nose
bull Fever and rash and Koplikrsquos spots and conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
How to develop a Case DefinitionMeasles definitionsbull Fever and runny nose
ndash Too sensitivendash Too many other illnesses produce same symptomsndash Call many illnesses ldquomeaslesrdquo
bull Fever and rash and Koplikrsquos spots and conjunctivitisndash Too specificndash Many cases of measles do not have all these signsndash Miss many real cases of measles
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
How to develop a Case Definition
CDC case definition
bull generalized maculopapular rash gt 3 days and fever and at least one of the following cough coryza or conjunctivitis
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Issues with sensitivity and specificitybull No rules about how sensitive or specific a case definition
should be bull Early stage of an outbreak investigation ndash to detect as many
cases as possible requires a sensitive case definition (eg a person with three or more loose stools in a 24-hour period)
bull Later stage the clinical picture is often clearer and the diagnosis is laboratory-confirmed can use a more specific case definition (eg laboratory-confirmed Salmonella infection)
bull A single case definition that suits all needs is rarebull Quite common for case definitions to change during an
investigation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Case definitions
Confirmed cases ndash positive laboratory result (isolation of the causative agent or positive serological test) This case definition has high specificity Patients with epidemiological link with patients
Probable cases ndash have the typical clinical features of the illness but without laboratory confirmation
Possible cases ndash have fewer or atypical clinical features This case definition has high sensitivity
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Example Salmonellosis
bull Clinical description An illness of variable severity commonly manifested by diarrhea abdominal pain nausea and sometimes vomiting Asymptomatic infections may occur and the organism may cause extraintestinal infections
bull Laboratory criteria for diagnosis Isolation of Salmonella from a clinical specimen
bull Case classification bull Confirmed a case that is laboratory confirmed bull Probable a clinically compatible case that is epidemiologically
linked to a confirmed case
Case Definitions for Infectious Conditions Under Public Health Surveillance MMWR 46(RR10)1-55 Publication date 05021997
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Case definitions1048707 Example of case definition used in the investigation of an
Escherichia coli O157 outbreak
bull A case ndash any resident with gastrointestinal illness in Area A within five days of attending the Area A Fair in June 2003
bull Cases may be further categorized as
bull Confirmed case gastrointestinal illness with microbiological confirmation of E coli O157
bull Probable case bloody diarrhoea or haemolytic uraemia syndrome without microbiological confirmation
bull Possible case non-bloody diarrhoea without microbiological confirmation
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Identifying cases
bull The cases that prompt an outbreak investigation often represent only a small fraction of the total number of people affected
bull To determine the full extent of the problem and the population at risk of illness an active search for additional cases should be undertaken
bull Methods for finding additional cases will vary from outbreak to outbreak
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Methods for identifying casesbull Easy to identify cases when involve clearly
identifiable groups for example persons attending the same wedding party
bull If an outbreak affects a restricted population (eg students in a school or factory workers) and if a high proportion of cases are unlikely to be diagnosed a survey of the entire population can be conducted
bull Cases may know other people with the same condition particularly among household members work colleagues classmates friends or neighbours
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Methods for identifying cases Directly contacting physicians hospitals
laboratories schools or other populations at risk Directly alert the public For example in outbreaks
caused by a contaminated commercial food product announcements in the media can alert the public
If the cause of outbreak is known review of laboratory surveillance data (unique subtype or biochemical or molecular feature) can help to find people with similar infections
Foodborne Outbreak Investigation Hanoi 1-5 June 2009
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
Referencesbull Foodborne Disease Outbreaks Guidelines for
Investigation and Control WHO 2008bull Centers for Disease Control and Prevention (CDC)
httpwwwcdcgovbull Gregg MB Field Epidemiology New York Oxford
University Press 2002 bull Case Definitions for Infectious Conditions Under
Public Health Surveillance bull MMWR 46(RR10)1-55 Publication date 05021997
- Define case and conduct case finding
- Introduction
- What is case definition
- Components of Case Definition
- Common components and examples of an outbreak case definition
- Examples of a case definition
- Concept of Sensitivity and Specificity
- Sensitivity and specificity
- How to develop a Case Definition
- Slide 10
- Slide 11
- Issues with sensitivity and specificity
- Case definitions
- Example Salmonellosis
- Slide 15
- Identifying cases
- Methods for identifying cases
- Slide 18
- References
-
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