Outbreak Investigation: The First 48 Rachel Radcliffe, DVM, MPH Career Epidemiology Field Officer Division of Infectious Disease Epidemiology West Virginia.

Outbreak Investigation:The First 48

Rachel Radcliffe, DVM, MPHCareer Epidemiology Field Officer

Division of Infectious Disease EpidemiologyWest Virginia Dept. of Health and Human Resources

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Objectives

• Explain the definition of an outbreak

• Describe initial actions of outbreak investigation

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What is an Outbreak?

• Occurrence of more cases than expected

• Localized increase in the incidence of disease

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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

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To Investigate or Not Investigate?

• Variety of Factors to Consider– Disease – Health department resources– External factors

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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

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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

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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

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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

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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

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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

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Implement Control Measures

• Determined by clinical picture

• May change as outbreak continues

• Example:– Implement droplet precautions when

outbreak of respiratory illness reported

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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

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Parts of a Case Definition

• Clinical criteria

• Laboratory criteria

• Restrictions by person, place, and time

• Do not include exposure or risk factor criteria

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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

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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

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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

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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

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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

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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

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Suspected Influenza Outbreak Report

• Daycare reports multiple students with influenza

• Parents calling daycare panicked

• What are your next steps?

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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

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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

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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

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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

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Shingles Outbreak Report

• Reported from nursing home• Four residents with shingles-like rash• Shingles not infectious

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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

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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!

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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

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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

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Thank You

Questions?

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