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Approach to Outbreak Investigations

Approach to Outbreak Investigations. Danae Bixler, MD, MPH Infectious Disease Epidemiology Program. 10 Steps of Outbreak Investigation (CDC). 1. Prepare for fieldwork Research the disease Make administrative arrangements Clarify your role 2. Establish the existence of an outbreak

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Approach to Outbreak Investigations

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  1. Approach to Outbreak Investigations Danae Bixler, MD, MPH Infectious Disease Epidemiology Program

  2. 10 Steps of Outbreak Investigation (CDC) 1. Prepare for fieldwork • Research the disease • Make administrative arrangements • Clarify your role 2. Establish the existence of an outbreak • Does the observed number of cases exceed the expected number? WVDHHR/BPH/OEHP/DSDC/IDEP

  3. 10 Steps of Outbreak Investigation (CDC) 3. Verify the diagnosis • Speak directly with persons who are affected 4. Define and identify cases • Establish a case definition • Identify and count cases • Line listing WVDHHR/BPH/OEHP/DSDC/IDEP

  4. 10 Steps of Outbreak Investigation (CDC) 5. Describe and orient the data in terms of time, place and person • Outbreak curve • Map • Identify demographic and other characteristics of persons at risk 6. Develop hypotheses • Open-ended and wide-ranging interviews with a few people WVDHHR/BPH/OEHP/DSDC/IDEP

  5. 10 Steps of Outbreak Investigation (CDC) 7. Evaluate hypotheses • Comparison: hypotheses with established facts • Analytic epidemiology • Cohort studies (RR; 95% CI) • Case-control studies (OR; 95% CI) 8. Refine hypotheses and carry out additional studies WVDHHR/BPH/OEHP/DSDC/IDEP

  6. 10 Steps of Outbreak Investigation (CDC) 9. Implement control and prevention measures • Should occur as soon as information is available 10. Communicate findings WVDHHR/BPH/OEHP/DSDC/IDEP

  7. 3/1/2001: Illness in 28 of 60 staff of a Family Medicine Clinic • Predominant symptom = vomiting • Onsets: late PM of February 28 and early AM of March 1, 2001 • Physicians, nurses, residents • Staff had eaten three meals in common: • Mon: catered meal of Heavenly Ham • Tue: Mardi-Gras pot-luck • Wed: food from Subway WVDHHR/BPH/OEHP/DSDC/IDEP

  8. Step 2: Establish the existence of an outbreak • Occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time. WVDHHR/BPH/OEHP/DSDC/IDEP

  9. Step 1: Prepare for Fieldwork • Investigation: • Appropriate scientific knowledge, supplies, equipment WVDHHR/BPH/OEHP/DSDC/IDEP

  10. Vomiting as a Chief Complaint • Viral gastroenteritis • Rotavirus (infant) • Norovirus (older child / adult) • Food poisoning due to pre-formed toxin • Staphylococcus aureus • Bacillus cereus • Non-infectious (Sb, As, Cd, Cu, Fl, Zn, etc.) WVDHHR/BPH/OEHP/DSDC/IDEP

  11. Incubation Periods for Suspect Infectious Agents WVDHHR/BPH/OEHP/DSDC/IDEP

  12. Step 1 & 9: Prepare for Fieldwork and Implement Control Measures • Administration • Make travel and coverage arrangements • Consultation (roles) • Collaboration on all steps (state / regional epi / LHD) • Work restriction for ill health care workers • ICP involvement • LHO involvement • IDEP (consultative role) WVDHHR/BPH/OEHP/DSDC/IDEP

  13. Step 3: Verify the Diagnosis • Through effort of the Regional Epidemiologist: • Routine stool cultures submitted through the hospital • Stool for Norovirus submitted to the CDC WVDHHR/BPH/OEHP/DSDC/IDEP

  14. Step 4: Establish a case definition and identify and count cases • 4a) Establish a case definition: • Initial case definition: persons employed by or assigned to the Family Medicine Clinic who called in sick on March 1, 2001 • 4b) Identify and count cases: • Twenty-eight individuals were identified. WVDHHR/BPH/OEHP/DSDC/IDEP

  15. Step 3, 5 and 6 Verify diagnosis. Do descriptive epidemiology and develop hypotheses.

  16. Open-Ended Interviews (3/1/01) N=10 persons who called in sick • Verify diagnosis: • Symptoms: • Sudden onset of profuse vomiting and diarrhea • Systemic symptoms, including headache, arthralgias, myalgias, weakness • Recovery (or near recovery):12 hours WVDHHR/BPH/OEHP/DSDC/IDEP

  17. Open-Ended Interviews (3/1/01) N=10 persons who called in sick • Descriptive Epidemiology: • Onset: late on 2/28; early AM and morning of 3/1 WVDHHR/BPH/OEHP/DSDC/IDEP

  18. Open-Ended Interviews (3/1/01) N=10 persons who called in sick • Hypothesis generation: • No common events outside of work • Attendance at: • Monday luncheon (2/26) – 3 (30%) • Mardi Gras pot luck (2/27) – 10 (100%) • Wednesday lunch (2/28) – 7 (70%) WVDHHR/BPH/OEHP/DSDC/IDEP

  19. Step 7: Evaluate hypotheses • Regional epidemiologist obtained the menu for the Mardi Gras luncheon • Questionnaire constructed (state) • Interview of a convenience sample: • Recovered / well individuals on-site • Local/ regional public health personnel • Ill individuals by phone • State staff WVDHHR/BPH/OEHP/DSDC/IDEP

  20. Back to Step 4: • Case: individual in attendance at the Mardi Gras luncheon (2/27/01) with illness characterized by vomiting or two or more episodes of diarrhea, and onset on or after February 28, 2001 • Control: individual in attendance at the Mardi Gras luncheon with no symptoms of illness the week of 2/26/02. WVDHHR/BPH/OEHP/DSDC/IDEP

  21. Study Population • 39 interviews • Exclusions: • 1 person ill, but did not meet the case definition • 1 did not attend the dinner • 3 had onset prior to 2/28/02 • Final population: N = 34 • 16 cases • 18 controls WVDHHR/BPH/OEHP/DSDC/IDEP

  22. And Back to Steps 3 and 5: Verify the diagnosis and perform descriptive epidemiology • Interviews allow refinement of • Descriptive epidemiology: outbreak curve (time) • Diagnosis WVDHHR/BPH/OEHP/DSDC/IDEP

  23. WVDHHR/BPH/OEHP/DSDC/IDEP

  24. Aches 10 (62%) Chills 10 (62%) Cramps 12 (75%) Diarrhea 13 (72%) Avg. 5.25 episodes Headache 11 (69%) Nausea 13 (81%) Vomiting 13 (83%) Avg. 5.3 episodes Fever 4 (25%) Characteristics of Illness (N=16) WVDHHR/BPH/OEHP/DSDC/IDEP

  25. Step 7: RR of illness for the exposure candied sweet potatoes = 0.69; (95% CI 0.13 to 3.56); p=1.0) WVDHHR/BPH/OEHP/DSDC/IDEP

  26. Step 7: RR of illness for the exposure chocolate cake = 0.97; 95% CI 0.46 to 2.03); p=0.78 WVDHHR/BPH/OEHP/DSDC/IDEP

  27. Step 7: RR of illness for the exposure seafood jambalaya = 1.45; 95% CI 0.70 to 2.98); p=0.50 WVDHHR/BPH/OEHP/DSDC/IDEP

  28. Step 7: RR of illness for the exposure Mardi Gras punch = 4.9; 95% CI 1.32 to 18.25); p=0.004) WVDHHR/BPH/OEHP/DSDC/IDEP

  29. Step 8: Refine the hypothesis How could the punch have become contaminated?

  30. Other data • Nursing home outbreak (same week): • Onsets consistent with person-to-person spread • Background illness • Community • Family Practice Center WVDHHR/BPH/OEHP/DSDC/IDEP

  31. March 3, 2001: How was Mardi Gras punch made? • Bottled grape juice • Unsweetened canned pineapple juice • Sprite • Homemade ice rings • Water • Sliced fruit • Doubloons • Sliced fruit • Mixed in bowl ‘found on top of refrigerator’ WVDHHR/BPH/OEHP/DSDC/IDEP

  32. Ice ring –household A City water Person who made it had ‘GI distress’ the day of the event Ice ring –household B Well water All members of family of this household sequentially had similar illness over the previous month Homemade Ice Rings WVDHHR/BPH/OEHP/DSDC/IDEP

  33. Step 9,10: Control Measures / Communication • Contacted Regional Epidemiologist / Clinic Director March 3, 10:30 AM • Preliminary results of analysis suggest Mardi Gras Punch is the most likely culprit • No evidence for contamination of commercial food product • Recommend: exclusion of ill persons and good handwashing WVDHHR/BPH/OEHP/DSDC/IDEP

  34. Timeline • Thursday, March 1, 2001 • Notification; approximately 3:00 PM • Open-ended interviews • Study design • Friday, March 2, 2001 • Interviews using a standard questionnaire • Data entry • Analysis completed 10:30 PM • Saturday, March 3, 2001 • Phone interview of persons who made the punch 8:00 AM • Preliminary results shared with the regional epidemiologist and clinic director 10:30 AM WVDHHR/BPH/OEHP/DSDC/IDEP

  35. Step 8: The lab gets the last word • Environmental Specimen: • Water sample from kitchen tap of household B: • (+) total coliforms • (+) E coli WVDHHR/BPH/OEHP/DSDC/IDEP

  36. Step 8: The lab gets the last word • Human Specimens • 12 stool specimens • Negative for Salmonella, Shigella, Yersinia and Campylobacter in the clinical laboratory • 10 stool specimens • PCR positive for NLV at CDC • Identical nucleotide sequence WVDHHR/BPH/OEHP/DSDC/IDEP

  37. Conclusion • Mardi Gras punch was the source of an outbreak affecting approximately half the staff of a family medicine center • Contamination likely introduced by: • Fecally-contaminated well water, OR • Hands of one of the people who prepared the punch; OR • (possibly) residual environmental contamination in household B. WVDHHR/BPH/OEHP/DSDC/IDEP

  38. Limitations • Incomplete response rate on the cohort study WVDHHR/BPH/OEHP/DSDC/IDEP

  39. Step 9: Implement control and prevention measures The well was taken out of service. WVDHHR/BPH/OEHP/DSDC/IDEP

  40. Step 10: Communicate findings • Written outbreak report distributed with laboratory results approximately one month later to: • LHD • Clinic Director • OLS • Environmental Health • Regional Epidemiologist • CDC WVDHHR/BPH/OEHP/DSDC/IDEP

  41. Conclusions • NLV outbreaks are: • Good practice • Important to investigate because of the total burden of disease • Cause of significant disability and death, especially in vulnerable populations • Challenging to investigate because laboratory diagnosis is not readily available WVDHHR/BPH/OEHP/DSDC/IDEP

  42. Conclusions • 10 steps of outbreak investigation • Conceptual • Provide a logical progression for the investigation • Can / should be taken out of order (with caution) WVDHHR/BPH/OEHP/DSDC/IDEP

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