Following 36 diagnosed cases of E. coli O:157 in the U.K., an extensive epidemiologic investigation* revealed cucumbers imported from Holland as the vehicle of infection. The implicated product was served in restaurants and home-prepared salads.  Despite the fact that a major restaurant chain involved had conducted microbiological assays as a routine QC procedure, the pathogen common to patients was isolated from samples of cucumbers and was shown to to be identical to the outbreak strain applying whole genome sequencing. 

The outbreak demonstrates the diagnostic challenge associated with widespread distribution of a contaminated food from a single source.  The case report also confirms that database surveillance systems can detect outbreaks involving small numbers of patients. With application of whole genome sequencing, epidemiologists can identify a vehicle of infection and trace back to source.

*Mulchandani,R. Outbreak of Shiga toxin-producing Escherichia coli O:157 linked with consumption of a fast-food product containing imported cucumbers, United Kingdom, August 2020. International Journal of Infectious Diseases doi.org/10.1016/j.ijid.2021.04.001