Outbreak Investigation: The First 48 Rachel Radcliffe, DVM, MPH Career Epidemiology Field Officer Division of Infectious Disease Epidemiology West Virginia.
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Outbreak Investigation:The First 48
Rachel Radcliffe, DVM, MPHCareer Epidemiology Field Officer
Division of Infectious Disease EpidemiologyWest Virginia Dept. of Health and Human Resources
1
Objectives
• Explain the definition of an outbreak
• Describe initial actions of outbreak investigation
2
What is an Outbreak?
• Occurrence of more cases than expected
• Localized increase in the incidence of disease
3
How are outbreaks detected?
• Review and analyze surveillance data
• Clinicians alert health departments to unusual events or clusters
• Receive reports by patients or other community members
4
To Investigate or Not Investigate?
• Variety of Factors to Consider– Disease – Health department resources– External factors
5
Steps of Outbreak Investigation
• Prepare for field work• Establish existence of outbreak• Verify diagnosis• Implement control and prevention measures• Construct a working case definition• Find cases systematically and record information• Descriptive epidemiology• Evaluate hypotheses epidemiologically• Reconsider, refine, and re-evaluate hypotheses• Evaluate lab/environmental findings• Initiate or maintain surveillance• Communicate findings
6
Steps of Outbreak Investigation
• Prepare for field work• Establish existence of outbreak• Verify diagnosis• Implement control and prevention measures• Construct a working case definition• Find cases systematically and record information• Descriptive epidemiology• Evaluate hypotheses epidemiologically• Reconsider, refine, and re-evaluate hypotheses• Evaluate lab/environmental findings• Initiate or maintain surveillance• Communicate findings
7
Prepare for Field Work
• Scientific and investigative issues– Review literature– Consult subject matter experts– Consult laboratory– Supplies and equipment
• Management and operational issues– Designate team leader– Communications plan– Travel, lodging, and transportation
8
Establish Existence of an Outbreak
• Try to determine baseline occurrence of disease
• Compare observed number of cases to expected number of cases for disease
• Consider other possible causes for increase
9
Verify the Diagnosis
• Similar to verifying existence of outbreak
• Review clinical findings and lab results– Consult with clinical experts
• Visit / Interview patients with disease
• Summarize clinical findings with frequency distributions
10
Line Lists
• List of cases with demographic, clinical, and possibly laboratory information
• Examine number of affected to determine if over baseline– Establish existence of outbreak
• Examine clinical findings and lab results– Verify diagnosis
11
12
Implement Control Measures
• Determined by clinical picture
• May change as outbreak continues
• Example:– Implement droplet precautions when
outbreak of respiratory illness reported
13
Construct a Working Case Definition
• Standard set of criteria for deciding whether an individual should be classified as having disease of interest
• Not 100% accurate
• Use broad case definition early in investigation
• Revise as investigation continues
14
Parts of a Case Definition
• Clinical criteria
• Laboratory criteria
• Restrictions by person, place, and time
• Do not include exposure or risk factor criteria
15
Different Categories of Case Definitions
• Confirmed – Clinical criteria plus lab confirmation
• Probable– Clinical criteria without lab confirmation
• Suspect– Sometimes used– Fewer clinical criteria
• Categories helpful when diagnosis uncertain
16
Example Case Definition
• Three or more loose stools or episodes of diarrhea in a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010
17
Example Case Definition Clinical Criteria
• Three or more loose stools or episodes of diarrhea in a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010
18
Example Case Definition Person Restriction
• Three or more loose stools or episodes of diarrhea in a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010
19
Example Case Definition Place Restriction
• Three or more loose stools or episodes of diarrhea in a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010
20
Example Case Definition Time Restriction
• Three or more loose stools or episodes of diarrhea in a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010
21
Suspected Influenza Outbreak Report
• Daycare reports multiple students with influenza
• Parents calling daycare panicked
• What are your next steps?
22
Suspected Influenza Outbreak Initial Investigation Steps
• Determine existence of an outbreak• Verify diagnosis– Line list– Use standard ILI case definition• Fever >100 degrees F plus cough or
sore throat– Discuss potential laboratory testing• Nasopharyngeal swabs
23
Suspected Influenza Outbreak Line List
Patient ID Class
Highest Temp Cough
Sore Throat
12345
InfantToddlerPre-K
After SchoolToddler
101989998
97.5
NYNYN
NNYNN
* There are 50 kids in the daycare center
24
Suspected Influenza Outbreak Frequency Distributions
• 1 out of 5 (20%) have fever > 100 degrees F• 2 out of 5 (40%) have cough• 1 out of 5 (20%) have sore throat• 1 out of 5 (20%) has not symptoms• None meet ILI case definition
25
Suspected Influenza Outbreak Frequency Distributions
• 1 out of 5 (20%) have fever > 100 degrees F• 2 out of 5 (40%) have cough• 1 out of 5 (20%) have sore throat• 1 out of 5 (20%) has not symptoms• None meet ILI case definition• Not likely to be influenza outbreak
26
Shingles Outbreak Report
• Reported from nursing home• Four residents with shingles-like rash• Shingles not infectious
27
Shingles Outbreak Report
• Reported from nursing home• Four residents with shingles-like rash• Shingles not infectious• Recommended to consult with dermatologist
to verify shingles diagnosis– 1 diagnosed with shingles– 2 diagnosed with eczema– 1 diagnosed with contact dermatitis
28
Shingles Outbreak Report
• Reported from nursing home• Four residents with shingles-like rash• Shingles not infectious• Recommended to consult with dermatologist
to verify shingles diagnosis– 1 diagnosed with shingles– 2 diagnosed with eczema– 1 diagnosed with contact dermatitis
• Outbreak ruled out!
29
Steps of an Outbreak Investigation
• Prepare for field work• Establish existence of outbreak• Verify diagnosis• Implement control and prevention measures• Construct a working case definition• Find cases systematically and record information• Descriptive epidemiology• Evaluate hypotheses epidemiologically• Reconsider, refine, and re-evaluate hypotheses• Evaluate lab/environmental findings• Initiate or maintain surveillance• Communicate findings
30
Steps of an Outbreak Investigation
• Prepare for field work• Establish existence of outbreak• Verify diagnosis• Implement control and prevention measures• Construct a working case definition• Find cases systematically and record information• Descriptive epidemiology• Evaluate hypotheses epidemiologically• Reconsider, refine, and re-evaluate hypotheses• Evaluate lab/environmental findings• Initiate or maintain surveillance• Communicate findings
31
Thank You
Questions?
32
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