August 9, 2022

Protracted Intermittent Salmonella Outbreak Linked to Michigan Restaurant

In the Centers for Disease Control’s Morbidity and Mortality Weekly Report (MMWR) for the week of August 20, 2021, a report details the protracted intermittent Salmonella outbreak that was linked to a restaurant in Michigan from 2008 to 2019. The Salmonella Mbandaka contamination was impossible to eradicate, and the restaurant was permanently closed in 2018.

Protracted Intermittent Salmonella Outbreak Linked to Michigan Restaurant

In 2018, Michigan public health officials found that a single restaurant in southwest Michigan was the source for the Salmonella Mbandaka infections since 2008. Isolates from 36 ill persons shared two highly related pulsed-field gel electrophoresis patterns and highly related whole genome sequencing subtypes.

The first focus of the investigation was on food items. Sporadic case definitions over years, along with difficulty in food history recollection delayed the source identification. The Michigan Department of Health and Human Services, along with the Kalamazoo County Health and Community Services Department collected specimens, conducted multiple rounds of environmental testing, and visited the restaurant many times.

Fifteen of the 36 patients had the outbreak subtype isolated in urine, and 12 patients had urinary symptoms without diarrhea or vomiting, which is unusual. It is true that a higher proportion of certain Salmonella serogroups including Mbandaka can be isolated from urine.

As it turns out, the investigation revealed that environmental samples and stool specimens from asymptomatic restaurant employees tested positive for the outbreak strain of Salmonella Mbandaka. A complicated association between the environment and employees caused the illnesses. As a result, the report states that exclusion or restriction of asymptomatic food workers with positive nontyphoidal Salmonella should be considered as part of restaurant outbreak mitigation.

Most restaurant Salmonella outbreaks occur through undercooked or contaminated food products. But a study of 23 restaurant-associated salmonellosis outbreaks found that “restaurants with Salmonella-positive environmental samples had a higher proportion of Salmonella-positive food workers and longer outbreak durations than restaurants with negative environmental samples.

The length of this outbreak shows that Salmonella can be pervasive in restaurant in environments. It also points to the importance of hygienic restaurant policies and practices, and challenges in source identification when food poisoning cases occur intermittently. The 2009 FDA Food Code did not include asymptomatic nontyphoidal Salmonella infections among the five specific foodborne pathogens for which exclusion and restriction requirements are set out. the 2017 FDA Food Code did, so it was used for guidance.

The restaurant voluntarily and permanently closed in late 2018 and food, dishes, storage, soft goods, chairs, and tables were destroyed. The building was deemed ineligible for food production or storage relicensurc.

Nettleton WD, Reimink B, Arends KD, et al. Protracted, Intermittent Outbreak of Salmonella Mbandaka Linked to a Restaurant — Michigan, 2008–2019. MMWR Morb Mortal Wkly Rep 2021;70:1109–1113. DOI: icon.

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