A study was conducted to determine the source of an outbreak of E.coli O26:H11 infection occurring from December 2018 through May 2019. The outbreak involved 21 cases in nine states with three hospitalizations. Pulse-field gel electrophoresis (PFGE) patterns of isolates from patients resembled E.coli from a July 2020 outbreak involving ground beef. Subsequent genome multilocus sequence typing confirmed that the outbreak was due to a different vehicle of infection.

Interviews with patients suggested consumption of homemade dough or batter preceding illness.  Concentrating on this potential source, officials in Rhode Island were able to isolate the implicated STEC O26 from an intact bag of flour.  Six of the patients had purchased flour from the same store which derived product from a mill in Buffalo, NY.  Based on the investigation, a recall was initiated.

The study demonstrated the following principles common to foodborne outbreaks:

• PulseNet and FoodNet databases are able to detect outbreaks involving a small number of patients distributed across many states.
• Whole genome sequencing enables investigators to correlate a specific food item with outbreaks.
• Investigations and resolution of foodborne outbreaks is facilitated by close cooperation between the CDC and state and county health authorities.
• Resolution of foodborne infections requires a combination of traditional shoe leather epidemiology including patient interviews coupled with sophisticated laboratory assays such as whole genome sequencing.