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2014-2017 Bacterial Pathogens in Fresh Leafy Vegetables


Fresh leafy vegetables are frequently consumed by Canadians in all age groups. Unfortunately, they have been associated with numerous outbreaks of foodborne illnesses worldwide. Fresh leafy vegetables can become contaminated with pathogens during production, harvest, post-harvest handling, packaging and distribution. Since fresh leafy vegetables are often consumed raw, the presence of bacterial pathogens creates a potential risk for foodborne illnesses.

Considering the factors mentioned above and their relevance to Canadians, fresh leafy vegetables (leaf lettuce, spinach and arugula) were selected for targeted surveys. The purpose of the surveys was to generate baseline information on the occurrence of pathogenic bacteria in fresh leafy vegetables. Over the course of this study (April 1, 2014 – March 31, 2017), a total of 5508 samples were collected from retail locations in 11 cities across Canada. Five thousand thirty-eight (5038) samples were tested for Salmonella species (spp.) and Shigella. Four hundred seventy (470) samples were tested for non-O157 Verotoxigenic Escherichia coli (non-O157 VTEC). All 5508 samples were also tested for Verotoxigenic Escherichia coli O157 (E. coli O157) and generic Escherichia coli (E. coli). Generic E. coli is an indicator of the overall sanitation conditions throughout the food production chain.

Salmonella spp., Shigella, and E. coli O157 were not found in any samples. Non-O157 VTEC (O-untypeable) was found in 1/470 (0.2%) samples. Elevated levels of generic E. coli (100<x≤1000 Colony Forming Units (CFU)/g or Most Probable Number (MPN)/g) were found in 25/5508 (0.5%) samples and high levels of generic E. coli (>1000 CFU/g or MPN/g) were found in 7/5508 samples (0.1%).

The Canadian Food Inspection Agency (CFIA) conducted appropriate follow-up activities such as additional sampling and facility inspections. Given the perishable nature of the products, the implicated products were no longer available on the market when the samples were declared as unsatisfactory and consequently no product recalls were issued. In addition, it was not possible to determine the source of the contamination, however corrective actions were implemented by the facilities.

Overall, our survey results suggest that almost all fresh leafy vegetables are safe for consumption. They can however be found to have elevated and high levels of generic E. coli and on rare occasions non-O157 VTEC. Consequently, as with all foods, safe handling practices are recommended for producers, retailers and consumers.

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