Outbreak! How to Recognize, Investigate and Control Outbreaks

1. Outbreak!How to Recognize, Investigate and Control Outbreaks Katherine Feldman, DVM, MPH, DACVPM Assistant Director Center for Public and Corporate Veterinary Medicine

2. We will discuss… • Why investigate outbreaks? • The steps in outbreak investigation

3. What is an outbreak? • More cases of a particular disease than expected in a given area, or among a specific population, over a particular period of time • The number of expected cases varies

4. Is 1 case of leptospirosis in a dog in Baltimore an outbreak? Is 1 case of foot-and-mouth disease in a dairy cow in Montgomery County an outbreak?

5. Why investigate outbreaks?

6. Why investigate outbreaks? • Protect the community’s health • Remove the source of infection • Provide prevention guidance • Address concerns in the community • Increased knowledge base • Completing the clinical picture • Identify new etiologic agents • Identify new routes of transmission

7. New pathogens • HIV • SARS • Old pathogens in new contexts • Monkeypox • West Nile virus • New modes of transmission / risk factors • Poultry exposure for human AI in Hong Kong • Off-farm rendering for LPAI in VA • Exposure to potting soil for Legionella infection

8. Definitions • Outbreak – What I said earlier • Epidemic – Same as above • Cluster – Same as above, sort of • Epizootic – Same as above, but specific to animals • Risk factor • An attribute or exposure associated with increased probability of a specified outcome • Protective factor • An attribute or exposure associated with decreased probability of a specified outcome

9. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

10. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

11. An Outbreak in the Clinic… • May be limited in scope and impact • Preparation includes • Coordination with clinic staff • Data collection equipment assembled • Computer • Paper • Pencil • Calculator • Records pulled

12. An Outbreak in the Community… • Notification of people who “need to know” • Coordination with investigation partners • Assembly of equipment • Data collection • Communications • Clothing • Laboratory • Travel preparation

13. Probable Partners • Clinicians • Epidemiologists • Laboratory scientists • Environmental scientists • Infection control practitioners • Decision makers • Communications experts • Law enforcement? • Others depending on context

14. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

15. Is This Really an Outbreak? • Need to determine (quickly) if current rate exceeds background • Many infectious diseases are reportable • Beware of artifactual changes • Change in reporting practices • New diagnostic tests • Increased clinician awareness

16. Is This Really an Outbreak? • In the clinic, pull records for same period last year and compare • Survey clinicians • Acquire absentee records • May need to proceed with investigation because of local pressures even if unsure outbreak exists

17. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

18. Never Assume Anything!

19. Confirm the clinical diagnosis • Confirm by standard laboratory techniques • If possible, visit the laboratory and verify in person • Do not need confirmation on every patient • Sometimes new agent • Proceed despite lack of diagnosis

20. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

21. Case Definition • Imperative to be systematic • Consists of clinical criteria and other criteria to specify subject, place, and time • Use simplest and most objective criteria • Apply definition equally and without bias • Degrees of certainty may be included (e.g., confirmed, probable, suspect)

22. subject and place A resident of XYZ convalescent home with bloody diarrhea and onset after 8/11/03 clinical time

23. Degrees of Certainty • Confirmed A resident of XYZ convalescent home with bloody diarrhea with onset after 8/11/03 and a positive stool culture for E. coli O157:H7 • Probable A resident of XYZ convalescent home with bloody diarrhea with onset after 8/11/03

24. Line Listing • Organizational tool (grid) to count cases by their characteristics • Rows contain information on individual cases • Columns contain variables of interest

25. Case Finding • Will vary by situation – sometimes obvious • Active surveillance • Clinicians • Hospitals • Laboratories • Schools • Public announcements • Surveys

27. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

28. Orient the Data in Terms of TIME • Epidemic “epi” curve • Graphic plotting of distribution of cases (y axis) by time of onset (x axis), using an appropriate time interval • Can assess • Magnitude of the outbreak • Possible mode of spread • Duration of the epidemic • A time interval of ¼ to ½ an incubation period works best

29. Point Source Epidemic

30. Continuous Common Source

31. Propogated Epidemic

32. Steps in Creating an Epidemic Curve • Identify date of onset for first case • Set the time interval • Create X-axis lead and end periods • Assign area equal to one case to Y-axis • Plot cases • Mark critical events in the outbreak • Add labels

36. Orient the Data in Terms of PLACE • Mapping can provide clues regarding • Source of agent • Nature of exposure • Dissemination of pathogens and who is at risk may be affected by • Water supply • Milk distribution routes • Sewage disposal outflows • Prevailing wind currents • Et cetera

38. Anthrax Outbreak, Sverdlovsk 1979

39. Orient the Data in Terms of SUBJECT • Knowing • Number of cases • When they became ill • Where they became ill • General characteristics will help in generating hypotheses and targeting prevention

40. Age and Sex Distribution Among Cases in an Outbreak of E. coli O157:H7

41. Age and Sex Distribution Among E. coli O157:H7 Infection Cases Reported to Selected Health Departments, 1997

42. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

43. Hypothesis Generation • Probably have good sense of source by this point in investigation • Hypothesis generating questionnaires • For foodborne outbreaks will ask about food consumption patterns in general • Consider “new” sources of infection but don’t forget the “usual” sources

44. Steps in an Outbreak Investigation • Prepare for field work • Establish the existence of an outbreak • Verify the diagnosis • Define and identify cases • Describe and orient the data in terms of time, place, and subject • Develop hypotheses • Evaluate hypotheses • Refine hypotheses and carry out additional studies • Implement control and prevention measures • Communicate findings

45. Epidemiologic Investigations • An outbreak of GI illness occurs • You describe cases by subject, time, place • You note all cases ate mushroom pizza at the same pizzeria on one particular evening… you hypothesize it’s the mushroom pizza • But what if there was a special offer that night, and EVERYONE (sick and not sick) ate mushroom pizza…. • Now that you have a hypothesis, you need to test it!

46. Types of Epidemiologic Investigations • Case-control studies • Identify cases • Identify appropriate control group • Collect exposure data on both groups • Compare • Cohort studies • Identify a group (cohort) based on exposure • In that group, collect information on exposure and case status • Compare

47. In both types of studies, the same information is collected for both sick and well subjects Statistical tests are used to compare the two populations with respect to various exposures

48. Ratio Measures of Association • Assess the strength or magnitude of the statistical association between the exposure and disease of interest • In case-control studies, the odds ratio is most commonly used • In cohort studies, the relative risk is most commonly used

49. Odds Ratios (OR) Compare odds of exposure among cases to odds of exposure among controls

50. Relative Risk (RR) Compare risk of disease among exposed to risk of disease among unexposed a / h1 c / h2 RR =