 Mystery Outbreak! Part 2
If you read Part 1 of this Mystery Outbreak, and
have been sitting on pins and needles, wait no more! Here is the thrilling
conclusion to the 2017 Salmonella Heidelberg outbreak associated with a fast
food chain in Anytown, Minnesota.
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Additional cases
In early November, additional cases of illness were
reported. Three cases reported eating at the North location, and one case at
the South location, all in the first week of October. EH staff called the store
owners to inform them that now both North and South store locations were
implicated in the outbreak.
Interventions
On November 1, MDH sanitarians visited the South location to
interview all employees. Both North and South stores were required to clean and
sanitize, and the North store continued screening employees for illness.
Managers
reported that the two stores typically do not share employees, however one
employee who was identified as an asymptomatic carrier had moved from the North
store to the South store.
More additional cases
On
November 22, a local hospital reported that a restaurant employee was
hospitalized and tested positive for Salmonella.
One week later, the same hospital identified another case of Salmonella. When interviewed by MDH, the
case reported that he and multiple ill family members had eaten at the South
store in late November.
Final interventions
On November 30, with these new cases identified, the
restaurant owner decided to voluntarily close both North and South locations at
the request of MDH.
While closed, the stores brought in an outside company to
clean and sanitize all surfaces. All employees were excluded from work until
they submitted two negative stool samples. The North store was required to
install an additional handwashing sink, employee training on handwashing was
conducted, and all food was discarded.
Minnesota Department of Agriculture (MDA) was contacted to
perform food product testing and to collect product samples from the North
store. They collected four samples of ground beef patties and 30 environmental
swab samples. All samples were negative for Salmonella.
The restaurant ownership also hired an independent company
to collect environmental samples, all of which were negative for Salmonella.
The
North store reopened on December 11, and the South store reopened on December
14 after all completing all required interventions.
Summary
In total, eight employees tested positive for the outbreak
strain of Salmonella Heidelberg.
Three were asymptomatic. The earliest positive stool samples were collected
from September 24 through December 12.
Forty-seven cases were identified; nine were hospitalized;
and illness onset dates ranged from August 12 to December 8.
Restaurant
records indicate that approximately two-thirds of meals served daily include a
beef patty. In comparison, all cases who could recall the foods they had eaten
reported eating food with a beef patty (n=12). Statistical analysis showed a
significant association between illness and beef patties as well as condiments
only served on burger patties.
Conclusion
Multiple
Salmonella-positive food employees,
and possible opportunities for both cross-contamination by food employees
facilitated by improper handwashing and glove use, were identified. It is
plausible that Salmonella was
introduced to the facility in a food product or food employee, and then
disseminated through infected food employees and cross-contamination.
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