Investigation of a Salmonella Montevideo Outbreak Related to the Environmental Contamination of a Restaurant Kitchen Drainage System, Québec, Canada, 2020-2021

In May 2020, the Direction de santé publique du CIUSSS de la Capitale-Nationale (DSPu) received a report from the Laboratoire de santé publique du Québec of a cluster of three cases of Salmonella enterica enterica, serogroup C1, serotype Montevideo. The epidemiological investigation identified a total of 67 cases between January 1, 2020, and August 13, 2021, 66% of which were directly linked to a restaurant in the area. The Salmonella strains from most of these cases were found to be identical by whole-genome sequencing (cluster code 2005MontWGS-1QC). The initial inspection of the restaurant by the competent authorities (Ministère de l'agriculture, des pêcheries et de l'alimentation du Québec) - including the evaluation of hygiene and food safety, the search for cases of illness among workers and food sampling - was unable to establish the source of the outbreak. Environmental samples showed that the restaurant's kitchen drains were contaminated with the same strain of Salmonella Montevideo as the cases in the outbreak. Several cleaning and disinfection methods were used repeatedly. When environmental sampling at the restaurant sites was repeatedly and consecutively negative, cases in the community stopped. The prior occurrence of a fire in the kitchen may have played a role in the contamination of the restaurant drains. In conclusion, public health professionals should consider drainage systems (plumbing) and possible aerosolization of bacteria as a potential source of a restaurant-related salmonellosis outbreak.