2009-2010 - Bacterial Pathogens and Generic E. coli in Tomatoes in the Canadian Market

Executive Summary

The Food Safety Action Plan (FSAP) aims to modernize and strengthen Canada's food safety system in order to better protect Canadians from unsafe food and ultimately reduce the burden of foodborne illness. The funds allocated under the FSAP allowed for the implementation of an enhanced surveillance program with an objective of collecting information on the priority hazards in various food products by conducting targeted surveys over a five-year period from 2008/09 to 2012/13. In the area of microbiological hazards in food, the targeted surveys focused on foodborne pathogens of concern in fresh produce and imported food ingredients.

In the last decade, fresh fruits and vegetables have been increasingly reported in association with foodborne illness, with tomatoes being the second most frequent vehicle in the produce associated outbreaks. Although these outbreaks have been mainly reported in the U.S., the microbiological quality of tomatoes in Canada remains of concern, as the supply sources are similar in both countries. For many years in Canada and the U.S. imported tomatoes have made up a large portion of the tomato consumption. Field-grown tomato production is seasonal in Canada and in many regions of the U.S., which in the fall, winter and spring is complemented by imports predominantly from Mexico. U.S.-grown tomatoes constitute about 25 percent of Canadian tomato imports.

Outbreaks associated with tomatoes have been predominantly linked to Salmonellae, followed by Norovirus and Hepatitis A virus. In the U.S., a single outbreak each of shigellosis and campylobacteriosis have been associated with contaminated tomatoes. In the past decade there has been a rapid increase in the market share for tomatoes grown using organic practices. The use of composted animal manure and plant debris in the production of organic produce has raised concerns about an increased likelihood of contamination with enteric pathogens, especially E. coli O157:H7. In contrast to pathogenic strains of E. coli, there are many strains of this bacterium that are harmless. These harmless strains inhabit the large intestine of humans and animals and are shed into the environment in feces. If pathogenic organisms are also present, they are shed alongside the harmless generic E. coli. Therefore, E. coli is considered to be the best available indicator for fecal contamination in produce, and its levels are used to assess the adherence to good agricultural/farming practices. Ultimately high numbers of E. coli in tomatoes may point to an inadequate agricultural/farming practises and/or lack of cleanliness and proper sanitary conditions during production, packaging, and/or storage.

Considering all these factors, tomatoes have been selected for enhanced surveillance under FSAP with an overall objective to gather baseline information on the occurrence of bacterial pathogens and indicator bacteria (E. coli) in tomatoes available to Canadians at retail. This targeted survey was designed to gather information on the presence and distribution of some bacterial pathogens of concern:

  1. Salmonella spp. and Shigella spp. in tomatoes,
  2. E. coli O157:H7 and E. coli O157:NM in organic tomatoes, and
  3. The presence, distribution, and levels of indicator bacteria, generic E. coli, in tomatoes.

In this survey a total of 1414 retail samples of fresh tomato were analysed, including imported (701 samples) and domestically produced (713 samples), conventional (1211 samples) and organically grown tomatoes (203 samples). These samples were analysed for bacterial pathogens of concern (Salmonellae and Shigellae) and indicator bacteria (E. coli). In addition, all samples of organic tomatoes, both imported (101 samples) and domestic (102 samples) and a comparable number of conventional domestic tomatoes (103 samples) were tested for the presence of E. coli O157:H7 and E. coli O157:NM. In none of the samples analysed the bacterial pathogens and generic E. coli were detected, which suggests Good Agricultural Practices and sanitary conditions during packaging, transportation and storage.

Up-to-date results of various tomato-monitoring programs show similar results to those obtained under this survey. These findings combined with the epidemiological evidence linking foodborne illness to the consumption of tomatoes, suggest that the contamination of tomatoes with pathogens is sporadic. The sample size employed in this survey (1414 samples) allows us to conclude that the prevalence of these pathogens in retail tomatoes during this study was below 0.2%. To obtain a better estimate of the "true" prevalence of pathogens in tomatoes, a greater number of samples would be required.

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