What to know
Collecting purchase information and retail sampling are two reliable methods for gathering exposure and laboratory data, but sometimes the only way to solve an enteric disease outbreak is to look in a case-patient's freezer. That's exactly what the Michigan OutbreakNet Enhanced (OBNE) site had to do in the fall of 2022 in a multi-state outbreak of Shiga toxin-producing Escherichia coli (STEC).
Feeling awful from falafel
In August 2022, four times the usual number of STEC cases were reported in Michigan, and multiple clusters were identified. After interviewing case-patients, a few common exposures stood out to investigators. Multiple case-patients reported eating at the same fast-food chain, and, for one cluster, all case-patients reported shopping at the same grocery store chain.
Because all case-patients reported shopping at the same grocery store chain, Michigan investigators decided to gather purchase data through credit card records. Unfortunately, they hadn't previously worked with this chain, which made the process of collecting records more complicated than expected. After multiple requests for their credit card numbers, case-patients began to worry about disclosing this information, and investigators worried their outbreak investigation would go no further.
However, while struggling to gather credit card information, interviewers were beginning to detect a strong signal for falafel, a deep-fried ball or patty made of beans and spices, through their conversations with case-patients. Hopeful that they had a chance at solving the outbreak, investigators attempted to collect falafel from the reported grocery store chain. Unfortunately, they hit another obstacle: falafel was not available in any store they visited or through online ordering, so sample collection from the store had to be cancelled.
Two months and several barriers after identifying this outbreak, investigators caught a break. An OBNE student interviewer identified a case-patient who had eaten the suspected falafel, had some left in their freezer, and was willing to provide it to Michigan investigators to sample.
In October, laboratory scientists at the Michigan OBNE site detected E. coli in the falafel collected from the case-patient's freezer, leaving one question: was this the same E. coli making people sick? To answer this question, investigators used a technique called whole genome sequencing (WGS). WGS is a laboratory technique used to determine relatedness of bacteria to detect clusters and link people and potential sources of their illnesses. Testing showed the E. coli in the falafel was closely related to the bacteria found in case-patients meaning that after months of persistence, Michigan investigators had found the likely source of this multi-state outbreak, and a recall was issued.
This investigation might not have been solved without the strengths and determination of the Michigan OBNE site, including the strong partnerships among laboratory, epidemiology, and environmental health and the student interview team that identified the product available for sampling. The outbreak also identified a need to build and strengthen relationships with retail partners, including grocery stores, before outbreaks occur to expedite investigations and improve data collection, such as credit card information. Though this was a difficult outbreak to solve, the Michigan OBNE site was able to discover the source by leveraging their enhanced capacity for investigating enteric disease outbreaks, while also identifying areas for improvement to better prepare them for the next outbreak.