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

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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 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,

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,

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,

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,

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,

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 TempCough Sore Throat Infant Toddler Pre-K After School Toddler NYNYNNYNYN NNYNNNNYNN * 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