Investigation and Control of

Outbreaks of

Foodborne IllnessRalph Cordell, PhD

0

200040006000

8000100001200014000160001800020000

1988 1989 1990 1991 1992

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

Year

Nu

mb

er o

f ca

ses

rep

orte

d

Types of Foodborne OutbreaksTypes of Foodborne OutbreaksType 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.

Types of Foodborne OutbreaksTypes of Foodborne OutbreaksType 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.

Severity - persons must realize they are ill

Communication - must recognize others are ill

Notification - must contact local health

authorities

Investigation

FileReport

Type AType A

School OutbreakSchool 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...

Initial Field VisitInitial Field Visit5:00 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 …

Followup Field Visit -KitchenFollowup Field Visit -KitchenNovember 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...

Illness InterviewIllness 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)

Food History

Food item Ate Did not eat % Ate Ate Did not eat % Ate p-valueSchool lunch 33 1 97% 108 78 58% <0.0001Turkey 31 2 94% 102 6 94% NSDressing 28 5 85% 93 15 86% NSBeans 18 15 55% 55 53 51% NSMashed potatoes 24 9 73% 80 28 74% NSGravy 23 10 70% 78 30 72% NSMilk 33 0 100% 105 3 97% NSPumpkin pie 30 3 91% 97 11 90% NS

Ill Well

Food history information is summarized below Only eating a school lunch was associated with illness

Lab ResultsLab 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.

ConclusionsConclusionsThis 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.

Severity - must be sufficient that persons seek medical attention

Concern - physician must order appropriate tests to support a diagnosis

Case must be reported to health authorities

Surveillance must detect increase

Investigation

Report Filed

Type BType B

Community OutbreakCommunity OutbreakSeptember 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.

Initial InterviewInitial InterviewWe received reports of 3 additional hepatitis A cases involving persons from that area and had interviewed10 of these persons by 8PM. Nine reported that they routinely purchased lunch meats from a local market. We were also told that...

Case - Control StudyCase - Control Study

Odds ratio = 81, p = 0.0005

Cases Controls Buy lunch meat from deli A

Yes 9 1

No 1 9

Follow-up StudiesFollow-up StudiesInterviewed 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.

Conclusion and Recommendations 1Conclusion and Recommendations 1Outbreak 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.

Conclusion and Recommendations 2Conclusion 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.

Foodhandler

Distributor

Initial Source

Percent of cases who reported Percent of cases who reported eating sandwiches with tomatoes eating sandwiches with tomatoes

by day of onsetby day of onset

Days 1-2 Days 3-4

Ate sandwich with tomato Did not eat

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.

Steps to Investigate an Steps to Investigate an Outbreak 1Outbreak 1

Implementing control measures based on data.

Evaluating effectiveness of control measures.

Developing prevention strategies.

Steps to Investigate an Steps to Investigate an Outbreak 2Outbreak 2