2004 Public Health Training and Information Network (PHTIN) Series

1. 2004 Public Health Training and Information Network (PHTIN) Series

2. Site Sign-in Sheet Please mail or fax your site’s sign-in sheet to: Linda White NC Office of Public Health Preparedness and Response Cooper Building 1902 Mail Service Center Raleigh, NC 27699 FAX: (919) 715 - 2246

3. Outbreak Investigation Methods From Mystery to Mastery

5. 2004 PHTIN Training Development Team Jennifer Horney, MPH - Director, Training and Education, NCCPHP Pia MacDonald, PhD, MPH - Director, NCCPHP Amy Nelson, PhD Penny Padgett, PhD, MPH Sarah Pfau, MPH Amy Sayle, PhD, MPH Michelle Torok, MPH, Doctoral Candidate Drew Voetsch, MPH, Doctoral Candidate Aaron Wendelboe, MSPH, Doctoral student

6. Future PHTIN Sessions August 17th. . . . . . . . . .“Interviewing Techniques” September 14th. . . . . . .“Designing Questionnaires” October 12th. . . . . . . . . “Analyzing Data” December 14th. . . . . . . “Risk Communication” Each session will be on a Tuesday from 10:00 am - 12:00 pm (with time for discussion)

7. Session I – VI Slides After the airing of each session, NCCPHP will post PHTIN Outbreak Investigation Methods series slides on the following two web sites: NCCPHP Training web site: http://www.sph.unc.edu/nccphp/training/index.html North Carolina Division of Public Health, Office of Public Health Preparedness and Response http://www.epi.state.nc.us/epi/phpr/

8. Session II “Study Design”

9. Today’s Presenters Michelle Torok, MPH Graduate Research Assistant and Doctoral Candidate, NCCPHP Amy Sayle, PhD, MPH Mellon Writing Fellow, Duke University Mary Crabtree Workplace Safety Manager, Department of Environment, Health, and Safety, UNC Chapel Hill Sarah Pfau, MPH Moderator

10. “Study Design” Learning Objectives Upon completion of this session, you will: • Understand what an analytic study contributes to an epidemiological outbreak investigation • Understand the differences in methodology between cohort and case-control study designs • Understand how to select cases and controls in a case-control study design

11. “Study Design” Learning Objectives (cont’d.) • Be able to describe the advantages and disadvantages of alternative forms of questionnaire administration in an outbreak investigation • Know how to interpret odds ratios from case-control study data and risk ratios from cohort study data • Be able to describe short- and long-term control measures that might be implemented in a food borne illness outbreak investigation • Understand how to implement long-term control measures such as policy change at an institutional or community level

12. Session I Review

13. Session I Review • Detected an outbreak of gastroenteritis at a university in Texas, based on a March 11 complaint from a student • Conducted: • active case finding • chart reviews • hypothesis generating interviews • 75 cases detected by March 12

14. Session I Review (cont’d.) • Collected stool specimens • All negative for bacterial pathogens • Assume viral pathogen • Earliest date of exposure was March 5 • Conducted interviews with 7 of the earliest cases (all students) • Only commonality was 6 of 7 reported eating at deli bar of main campus cafeteria

15. Session I Review (cont’d.) • Developed a leading hypothesis with the main campus cafeteria as the suspect • No source food identified • Interviewed 30 of 31 cafeteria staff members • Staff member who declined interview worked at deli bar* * Today’s session includes a follow up investigation with this staff member

16. Session I Review (cont’d.) • Closed deli bar on March 12th based on: • Link between 6 out of 7 interviewed cases and a common food source • Several unsanitary food handling practices identified via an environmental health investigation

17. Basic Steps of an Outbreak Investigation • Verify the diagnosis and confirm the outbreak • Define a case and conduct case finding • Tabulate and orient data: time, place, person • Take immediate control measures • Formulate and test hypothesis • Plan and execute additional studies • Implement and evaluate control measures • Communicate findings

18. Next Step: Analytic Study • Test current hypothesis: “Main campus cafeteria / deli bar is source of infection” • What do we know? • What do we suspect? • What can we “prove”?

19. What do we know? • We know… • 75 cases reported by March 12 – all were students who lived on campus • All of cases sampled (n=7) reported eating at the main campus cafeteria • 6 of 7 at the deli bar • No illness among off-campus students, faculty, or community members

20. What do we suspect? • We suspect the main cafeteria is the source of infection • We also suspect the deli bar, in particular, may be the outbreak source

21. What can we “prove”? • Can we “prove” it? • Need to conduct an analytic study • Need a testable hypothesis

22. What hypothesis will be tested? • Main cafeteria vs. other dining halls? • Within the main cafeteria: • Deli bar vs. grill? • Salad bar vs. hot entrée? • Food item vs. food handler at deli bar?

23. Our Hypothesis A viral infection spread by food(s) or beverage(s) served at the university’s main cafeteria between March 5 and 10

24. Source Population Town residents (39,000) Students (12,000) 2400 on campus 2000 meal plan

25. Which Study Design? • Cohort or case-control?

26. Cohort Study

27. Definition of a Cohort In Epidemiology, “Any designated group of individuals who are followed or traced over a period of time.” - Last, JM. A Dictionary of Epidemiology, 3rd ed. New York: Oxford University Press, 1995

28. Cohort Study Types A cohort study analyzes an exposure / disease relationship within the entire cohort. • Prospective • The Framingham Study • Retrospective • Usually used in outbreak investigations

29. Cohort Study Design Exposed Not Exposed Develop Do Not Develop Do Not Disease Develop Disease Develop Disease Disease

30. Cohort Study Steps in a Cohort Study: • Identify Cohort • Administer Questionnaire • Analyze Data

31. Cohort Study Step 1 – Identify cohort • Entire student body (n=12,000) • On-campus students (n=2400) • On campus students with meal plan who mainly ate at cafeteria (n=2000) • Sick students (n=75) • Do not select cohort so that either everyone is exposed or everyone is diseased

32. Cohort Study Step 2 – Administer questionnaire • Step 2a – Determine exposure status • Main cafeteria • Deli bar • Food item • Step 2b – Determine disease status • Importance of well-defined case definition

33. Cohort Study Example Dartmouth University: 698 (13.8%) of 5060 students had conjunctivitis in spring 2002 • To identify risk factors... • web-based questionnaire set up • E-mail sent to 3682 undergraduates • No data entry-rapid analysis • 1832 (50%) responded An outbreak of conjunctivitis due to atypical Streptococcus pneumoniae. N Engl J Med. 2003;348 (12):1112-21.

34. Cohort Study Step 3 – Analyze data

35. Interpreting a Risk Ratio The risk ratio is the ratio of the risk of disease in exposed individuals to the risk of disease in unexposed individuals • RR=1.0 = no association between exposure and disease • RR>1.0 = positive association • RR<1.0 = negative association

36. Interpreting a Risk Ratio Example: Outbreak of conjunctivitis at Dartmouth College • RR = 2.5 • Disease = Conjunctivitis • Exposure = Attended a fraternity / sorority party “Students who attended a fraternity or sorority party had 2.5 times the risk of having conjunctivitis compared to students who did not attend a fraternity or sorority party”

37. Cohort Study • Preferred study design when: • Members of cohort are easily identifiable • Members of a cohort are easily accessible • Exposure is rare • There may be multiple diseases involved

38. Cohort Study Example • Recent norovirus outbreaks on cruise ships • Attempt to interview all passengers • Collect food history information MMWR: December 13, 2002 / 51(49);1112-1115

39. Cohort Study Examples • Shigellosis among swimmers in a Georgia park • Used park registry to identify park visitors Iwamoto M, Hlady G, Jeter M et al. Shigellosis among Swimmers in a Freshwater Lake-Georgia, 2003. Presented at the 53rd Annual Epidemic Intelligence Service Conference. Atlanta, GA. April, 2004. • Whirlpools and Methicillin-Resistant Staphylococcus aureus • Occurred on a college football team Begier EM, Barrett FK, Mshar PA et al. Body Shaving, Whirlpools, and Football: An Out break of Methicillin-Resistant Staphylococcus aureus Cutaneous Infections in a College Football Team-Connecticut, 2003. Presented at the 53rd Annual Epidemic Intelligence Service Conference. Atlanta, GA. April, 2004.

40. Question & Answer Opportunity

41. Case Control Study

42. Case-Control Study Design Exposed Not Exposed Exposed Not Exposed Disease No Disease “CASES” “CONTROLS”

43. Cohort versus Case-Control Study

44. Case-Control Study Steps in a Case-Control Study: • Identify the source population • Establish a case definition and select cases • Select controls • Analyze data

45. Case-Control Study Step 1 - Identify source population • Represents the population that gives rise to the cases; is similar to a cohort study • In the Texas case study, the source population is: all students who live on-campus

46. Case-Control Study Step 2 – Establish a case definition and select cases • A standard set of criteria for deciding disease status • Clinical criteria, time, place, and person

47. Study Hypothesis A viral infection spread by food(s) or beverage(s) served at the university’s main cafeteria between March 5 and 10 Case definition Vomiting or diarrhea (≥3 loose bowel movements during a 24-hour period) Onset on or after March 5, 1998 On-campus student seen at an emergency room or the Student Health Center Case Study Case Definition

48. Case-Control Study Step 3 – Select Controls • Represent source population • On-campus students in Texas case study • Collect same exposure information as for cases

49. Case-Control Study Step 3 – Select Controls (cont’d.) • Sources of controls • Random sample • Friends

50. Case-Control Study Step 4 – Analyze Data