ARCHIVED - 2009 - 2010 Investigating Bacterial Pathogens and Generic E. coli in Fresh Leafy Herbs

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Executive Summary

The Food Safety Action Plan (FSAP) aims to modernize and enhance Canada's food safety system in order to better protect Canadians from unsafe food and ultimately reduce the occurrence of foodborne illness.

In recent years, leafy herbs have been reported to be responsible for numerous global outbreaks of foodborne illness. The Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO) has ranked leafy herbs, along with leafy vegetables, as the highest priority in fresh fruits and vegetables in terms of microbiological hazards. After harvest, leafy herbs are subject only to minimal processing (e.g., cutting, trimming, sanitizing, washing, packaging) and are often consumed raw. As such, pathogens introduced during any step of production may not only survive but also multiply. The bacterial pathogens Salmonella, Verotoxin-producing Escherichia coli (E. coli) (VTEC), and Shigella were identified to be related to many outbreaks of foodborne illness associated with leafy herbs.

Considering these factors and their relevance to Canadians, leafy herbs have been selected as one of the priority commodity groups of fresh fruits and vegetables for enhanced surveillance under the FSAP.

During four annual microbiological targeted surveys (2009/10 - 2012/13), over 5000 leafy herb samples will be collected and tested for the presence of pathogens of concern in leafy herbs available to Canadians at retail. This targeted survey (2009/10) focused on bacterial pathogens of concern and generic E. coli (as indicator bacteria of fecal contamination). The main objectives of this survey were to generate baseline surveillance data on:

  • the presence and distribution of bacterial pathogens of concern: E. coli O157:H7/NM, Salmonella species (spp.), and Shigella spp.; and
  • the presence, distribution and levels of generic E. coli in fresh leafy herbs available in the Canadian retail market.

In this survey, a total of 1,224 retail samples of leafy herbs were collected and analysed, including 816 imported and 408 domestically produced samples. Pathogenic bacteria and generic E. coli were not detected in the majority of samples (98.4%). A total of nine samples (0.7%) were found to be unsatisfactory. One sample (0.08%) was unsatisfactory due to the presence of Salmonella and the other eight samples (0.7%) were unsatisfactory due to high levels of generic E. coli (>1000 colony forming units (CFU)/g).

E. coli O157:H7, E. coli O157:NM (non-motile), and Shigella spp. were not detected in any of the herb samples in this survey. In addition, elevated levels of generic E. coli were found in 10 samples (0.8%). These samples were assessed as investigative and requiring further evaluation given that E. coli counts were elevated but below the unsatisfactory threshold of 1000 CFU/g. Evaluation of these samples did not result in any follow-up activities. To assist in the food safety investigations, the serotypes and pulsed field gel electrophoresis (PFGE) pattern (i.e., DNA typing) were identified from the isolates submitted from the one Salmonella positive sample.

Of the nine unsatisfactory samples, eight were imported (8/816, 1.0%) and one was domestically produced (1/408, 0.2%). The unsatisfactory imported herb samples originated from Mexico, the United States, and the Dominican Republic. All unsatisfactory samples were subject to food safety investigations and appropriate follow-up activities were conducted by the CFIA. One product recall resulted from the referral of the unsatisfactory samples and subsequent investigations. It is important to note that there were no reported illnesses associated with the consumption of the Salmonella-contaminated product in this survey.

Results of the 2009-10 survey indicate that the vast majority (98.4%) of the leafy herb samples were not contaminated with bacterial pathogens or with generic E. coli, an indicator used by the Agency to assess general sanitation and hygiene practices throughout the production chain. The study revealed that a low percentage (1.6%) of the leafy herb samples was contaminated by microorganisms that could represent a potential source of foodborne illness; however, no reported illnesses were associated with consumption of any of the product type in this survey during the time of the study. Contamination in these few samples could be the result of inadequate practices during production, packaging, or storage. Results of the three remaining microbiological targeted surveys on leafy herbs will be released annually upon completion.

It is important to note that the food industry and retail sectors in Canada are ultimately responsible for the food they produce and sell, while individual consumers are responsible for the safe handling of the food they have in their possession. The CFIA as well as other jurisdictions such as provincial and municipal regulators do monitor the controls throughout the food production chains. Moreover, general advice for the consumer on the safe handling of foods is widely available. The CFIA will continue its surveillance activities and inform stakeholders of its findings.

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