Investigation and Control of Outbreaks of Foodborne Illness

1. Investigation and Control of Outbreaks of Foodborne Illness Ralph Cordell, PhD

3. Number of cases of outbreak-associated food poisoning reported to the US Centers for Disease Control by year 1988-1992 Number of cases reported Year

4. Types of Foodborne Outbreaks Type A Outbreak  Target population is identifiable - attendance lists, etc. - can determine incidence of illness.  Exposure represented by a known event though specific source may be unknown.  Pathogen is unknown.

5. Types of Foodborne Outbreaks Type B Outbreak  Target population is unknown - cases are identified through surveillance - must use case- control approach.  Exposure is unknown, best clues are demographic distribution of cases.  Pathogen is known.

6. Type A File Report Investigation Notification - must contact local health authorities Communication - must recognize others are ill Severity - persons must realize they are ill

7. School Outbreak Friday - November 21 - 4:30 PM Took call from the Vice-Principal at a local elementary school. They had been called by several parents who reported children becoming violently ill during the bus ride home from school...

8. Initial Field Visit 5:00 PM - Field visit to school A Fire officials were unable to detect gas leaks, exhaust fumes or elevated CO2. Contact with parents of children absent that day failed to detect similar cases. The only break from routine was …

9. Followup Field Visit -Kitchen November 24 Interviewed the 2 kitchen workers. They indicated that turkeys (12 birds) were cooked the previous day, cooled at room temp, and deboned by hand. Meat was placed in 4 large pans and refrigerated...

10. Illness Interview  Of 220 children; 34 (16%) were ill  14 of 25 (56%) 1st graders were ill  15 of 29 (52%) 2nd graders were ill  5 of 166 (3%) in other classes were ill  33/34 ill children(97%) had vomiting  10 (29%) experienced diarrhea  Based on a lunch exposure, the incubation period ranged from 3-6 hours (avg 4.3 hours)

11. Food History • Food history information is summarized below • Only eating a school lunch was associated with illness

12. Lab Results Culture of hand swab from worker A were negative  Hand swab from worker B were positive for a nontypable strain of Staphylococcus aureus  Culture of dressing were negative for Staphylococcus  Turkey had >1,000,000 Staph/gram  Turkey isolates were nontypable.

13. Conclusions This outbreak was due to turkey contaminated with an untypable toxigenic strain of Staphylococcus aureus. The most likely source was an infected foodhandler who contaminated the turkey during deboning. The stack of meat in at least one of the four refrigerated pans was so great that the center of the stack did not cool sufficiently.

14. Type B Report Filed Investigation Surveillance must detect increase Case must be reported to health authorities Concern - physician must order appropriate tests to support a diagnosis Severity - must be sufficient that persons seek medical attention

15. Community Outbreak September 12 - 10 AM The Infection Control Nurse (ICN) at a local hospital called to report 8 cases of hepatitis A infection. These involved 8 different households in 4 different but adjoining communities. All were adults and worked at different occupations throughout the area.

16. Initial Interview We received reports of 3 additional hepatitis A cases involving persons from that area and had interviewed 10 of these persons by 8PM. Nine reported that they routinely purchased lunch meats from a local market. We were also told that...

17. Cases Controls Buy lunch meat from deli A Yes 9 1 No 1 9 Case - Control Study Odds ratio = 81, p = 0.0005

18. Follow-up Studies Interviewed all employees of Store A - several confirmed as having hepatitis A - all onsets were consistent with being a case rather than source for infection in this outbreak. Interviewed deli employees and obtained blood samples for HAV IgM testing - none reported ill though 1 person had HAV IgM.

19. Conclusion and Recommendations 1 Outbreak of hepatitis A was due to contamination of lunch meats sold from deli section of store A. An infected employee was the most likely source for this contamination.  Immune globulin for all household contacts of cases to reduce secondary transmission in homes.

20. Conclusion and Recommendations 2  As the problem had occurred more than a month earlier, we had no way of knowing how physical conditions we observed differed from those during the period when transmission took place.  Discard all unpackaged or open food products from deli and thoroughly clean area.  Make sure staff wash hands after using the bathroom.

21. Epidemiologic Data Laboratory Data Solution

22. Foodhandler Distributor Establishment Case Initial Source

23. Percent of cases who reported eating sandwiches with tomatoes by day of onset Days 3-4 Days 1-2 Ate sandwich with tomato Did not eat

24. Steps to Investigate an Outbreak 1  Recognizing and verifying that there is a problem.  Developing hypotheses concerning possible causes.  Collecting and analyzing data to test hypotheses.  Modifying hypotheses based on results.

25. Steps to Investigate an Outbreak 2  Implementing control measures based on data.  Evaluating effectiveness of control measures.  Developing prevention strategies.