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BACKGROUND: In July 2014, Alberta Health Services noted an increase in E.coli O157:H7 illnesses in Alberta, Canada. Initial interviews found that exposure to Asian-style supermarkets or restaurants were commonly reported. An outbreak investigation was initiated in Alberta to find the source of the illnesses.
METHODS: A case was defined as a resident of or visitor to Alberta with an infection of E.coli O157:H7 with one the outbreak pulsed-field gel electrophoresis (PFGE) patterns; and illness onset occurring during July 1-Nov 13, 2014. Cases were interviewed with a standardized questionnaire to collect information on travel, animal contact, and exposure to restaurants, events, meat, produce, seafood, and dairy in the 7 days before illness onset. Exposure frequencies were calculated, supplier records for restaurants and community events were reviewed, and samples were taken at the restaurant, supplier, and slaughter level. PFGE analysis was performed on clinical, food, and environmental isolates and uploaded to the PulseNet Canada database.
RESULTS: A total of 119 cases were identified with illness onsets ranging from July 20 to October 6, 2014. Twenty-three cases (19%) were hospitalized and no deaths were reported. The median age of cases was 23 years (range = 1 – 82 years) and 76 cases (64%) were female. Commonly reported food items included: bean sprouts, beef, carrots, cucumbers, green onions, lettuce, and pork. The traceback investigation focussed on suppliers of these food items at restaurants where sub-clusters occurred. A common, local pork supply chain was identified among implicated restaurants. Over 1,000 food samples were tested; E.coli O157:H7 with the outbreak PFGE patterns were detected in raw pork and environmental samples, resulting in five food recalls. Inspections were conducted at 201 facilities and 64 special food handler education sessions were delivered during the outbreak.
CONCLUSIONS: The investigation found the source of the outbreak to be contaminated pork products produced and distributed in Alberta. To our knowledge, this is the second largest foodborne E.coli O157:H7 outbreak in Canadian history. A systematic traceback investigation focussing on restaurant clusters to explore multiple hypotheses helped identify a common, local pork supply chain. Pork is not a commonly recognized vehicle for E.coli infections, therefore it is important to consider it as a potential source in future E.coli outbreaks and to include pork in safe handling and cooking messaging to prevent foodborne illness.