Outbreak Investigation: The First 48

1. 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

2. Objectives • Explain the definition of an outbreak • Describe initial actions of outbreak investigation

3. What is an Outbreak? • Occurrence of more cases than expected • Localized increase in the incidence of disease

4. 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

5. To Investigate or Not Investigate? • Variety of Factors to Consider • Disease • Health department resources • External factors

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. 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

8. 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

9. 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

10. 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

11. 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

13. Implement Control Measures • Determined by clinical picture • May change as outbreak continues • Example: • Implement droplet precautions when outbreak of respiratory illness reported

14. 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

15. Parts of a Case Definition • Clinical criteria • Laboratory criteria • Restrictions by person, place, and time • Do not include exposure or risk factor criteria

16. 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

17. 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

18. Example Case Definition Clinical Criteria • Three or more loose stoolsor 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 Person Restriction • Three or more loose stools or episodes of diarrheain a 24 hour period in a student or staff member of School A with illness onset after September 21, 2010

20. 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

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, 2010

22. Suspected Influenza Outbreak Report • Daycare reports multiple students with influenza • Parents calling daycare panicked • What are your next steps?

23. 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

24. Suspected Influenza Outbreak Line List * There are 50 kids in the daycare center

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

26. 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

27. Shingles Outbreak Report • Reported from nursing home • Four residents with shingles-like rash • Shingles not infectious

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

29. 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!

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. 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

32. Thank You Questions?