Protracted, Intermittent Outbreak of Salmonella Mbandaka Linked to a Restaurant

Michigan, 2008-2019

William D. Nettleton, MD; Bethany Reimink, MPH; Katherine D. Arends, MPH; Douglas Potter, MBA; Justin J. Henderson, MPH; Stephen Dietrich, MS; Mary Franks, MPH


Morbidity and Mortality Weekly Report. 2021;70(33):1109-1113. 

In This Article

Epidemiologic Investigation

In 2012, KCHCSD was notified by MDHHS about Salmonella Mbandaka cases occurring intermittently since 2008 that were highly related by PFGE pattern. During 2012–2014, a restaurant was not yet associated, so a hypothesis-generating questionnaire was used to ensure capture of detailed patient food histories, which included closed-ended questions about frequently eaten food items, types of restaurants visited, and animal contact. In 2014, although investigations into common suppliers among several restaurants mentioned in food histories were ongoing and other restaurants were named by cases, as more information was collected from supplementary questionnaires, KCHCSD, MDHHS, and the Michigan Department of Agriculture and Rural Development discussed the association of a single restaurant (restaurant A) based on five known, confirmed cases to date reporting a meal at restaurant A. KCHCSD gathered additional information from restaurant A management regarding employee health and exposures, facility and equipment, food sources, and pest control. No further epidemiologic link was established from the interview with the restaurant, but continued cleanliness and maintenance citations occurred during 2014–2018. Additional Salmonella Mbandaka cases in 2017 prompted development of a detailed, outbreak-specific case questionnaire that included specific questions about restaurant A. As more cases were identified, an intensive investigation began in 2018. An outbreak case was defined as a case of confirmed Salmonella Mbandaka with one of two closely related PFGE patterns (TDRX01.0120 and TDRX01.0127), highly related WGS subtype identified by the MDHHS Bureau of Laboratories or CDC, or probable cases with clinically compatible illness and epidemiologic linkage to a confirmed case.

During September 2008–July 2019, a total of 35 primary cases (33 confirmed and two probable) and one confirmed secondary case were identified. Patients with confirmed cases ranged in age from 1.5–90 years (mean = 57 years; median = 64 years), and 26 (72%) patients were female. Several patients reported a history of chronic gastrointestinal issues that made determination of onset date difficult. Twenty-four (67%) patients reported vomiting or diarrhea, and 12 (33%) reported urinary tract infection. Six (17%) patients were hospitalized. Approximately 40% of patients had underlying medical conditions such as diabetes or cancer. Among 19 patients with a restaurant dining history, 17 reported eating at restaurant A. Patients were routinely interviewed at the time of local health department referral and reinterviewed, often weeks later, when Mbandaka serotype was reported. Thirteen patients, retrospectively identified from early in the outbreak period, were not candidates for reinterview because their onsets preceded identifying them as part of the outbreak by >1 month.

After implementation of the outbreak-specific questionnaire in 2017, nine patients with onset during August 2017–July 2019 reported having eaten at restaurant A (Figure). To determine whether restaurant A was mentioned in the food histories of other reported foodborne illnesses, Michigan public health officials reviewed restaurant A patronage and food histories of 1,166 persons with previously reported salmonellosis, campylobacteriosis, and shigellosis cases in southwest Michigan for restaurant dining history. The only patients who reported eating at restaurant A were those associated with this outbreak; no other patients mentioned the restaurant.


Cases of Salmonella Mbandaka outbreak subtype (N = 35), by month and year of illness onset* and restaurant A exposure — Michigan, September 2008–July 2019†
*Onset date was missing for five patients; for these cases, the date of referral to the health department was used.
†Pulsed-field gel electrophoresis was performed only on the top 20 Salmonella serotypes submitted to the Michigan Department of Health and Human Services Bureau of Laboratories from approximately 2009 to early 2010; the Salmonella Mbandaka serotype was rare and not a top 20 serotype.