The First Outbreak of Salmonella Enteritidis Infections Linked to Frozen Whole Kernel Corn in Canada, 2021-2022

An investigation into an outbreak of Salmonella enterica serovar Enteritidis (S. Enteritidis) infections in Canada was initiated in October 2021 after a cluster of cases was identified through whole-genome sequencing. A total of 118 cases were identified in five provinces, related by 0-4 whole-genome multilocus sequence typing allele differences. Cases became ill between September 6, 2021 (symptom onset date) and January 27, 2022 (specimen isolation date). The median age of cases was 30 years (range: 1-89 years), and 64% were female. Five hospitalizations and two deaths were reported. Early in the investigation, a cluster of illnesses was identified that ate at different locations of the same restaurant chain (Restaurant Chain A). Several hypothesis-generating methods were conducted to identify the source, including: case re-interviews, menu review, ingredient analysis, traceback investigations, and sampling of food items. These methods identified multiple fresh produce items as possible hypotheses, but the source of the outbreak was identified when a sample of Brand X Individually Quick Frozen (IQF) Corn from Restaurant Chain A tested positive for the outbreak strain of S. Enteritidis. In total, 87% (75/86) of cases reported exposure to, or potential exposure to, corn. Based on the distribution records, 91% (68/75) of these cases could be linked to the recalled Brand X IQF Corn, and of those, 88% (60/68) consumed food from Restaurant Chain A. This article summarizes the first known outbreak investigation of Salmonella associated with frozen corn in Canada and adds evidence to the potential food safety risks associated with frozen vegetables.