Investigation and Control

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Investigation and Control of Outbreaks of
Foodborne Illness
Ralph Cordell, PhD
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(No Transcript)
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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
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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.
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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.
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Type A
File Report
Investigation
Notification - must contact local health
authorities
Communication - must recognize others are ill
Severity - persons must realize they are ill
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School Outbreak

Friday - November 21 - 430 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...

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Initial Field Visit
500 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
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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...
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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)
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Food History

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

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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
gt1,000,000 Staph/gram ? Turkey isolates were
nontypable.

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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.
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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
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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.
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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...
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Case - Control Study
Odds ratio 81, p 0.0005
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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. Interviewe
d deli employees and obtained blood samples for
HAV IgM testing - none reported ill though 1
person had HAV IgM.
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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.
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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.
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Epidemiologic Data
Laboratory Data
Solution
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Foodhandler
Distributor
Establishment
Case
Initial Source
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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
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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.
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Steps to Investigate an Outbreak 2
? Implementing control measures based on data. ?
Evaluating effectiveness of control measures. ?
Developing prevention strategies.