2010-2011 Viral Pathogens in Leafy Vegetables and Green Onions


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, viruses have been increasingly recognized as a major cause of foodborne illnesses. Norovirus (NoV) and hepatitis A virus (HAV) are the most frequently reported human enteric viruses involved in foodborne illnesses. An expert committee of the FAO/WHO (Food and Agriculture Organization of the United Nations and World Health Organization) recently determined that NoV and HAV in fresh produce were one of the virus-commodity combinations of highest priority in terms of food safety. According to foodborne outbreak information provided by the Public Health Agency of Canada for the period between 1998 and 2010, NoV accounted for approximately one third of outbreaks associated with leafy vegetables worldwide, while HAV was the predominant pathogen in outbreaks associated with green onions. Leafy vegetables and green onions can become contaminated with enteric viruses through contact with human sewage or infected workers during primary production, harvest, post-harvest handling, processing, packaging, and distribution. Unlike bacteria, human enteric viruses cannot multiply in food, as they need to enter living human cells to replicate. However, they can remain viable in vegetables for extended periods of time, and may cause illness if ingested.

Considering the factors mentioned above and their relevance to Canadians, leafy vegetables and green onions have been selected for enhanced surveillance under the FSAP. Between 2008/09 - 2012/13, about 5,000 samples of fresh fruits and vegetables were collected from Canadian retail locations and tested for the presence of viral pathogens of concern.

The main objective of the 2010/11 targeted survey was to generate baseline surveillance data on viral pathogens NoV and HAV for imported and domestically produced leafy vegetables and green onions available in the Canadian market. In total, 1112 samples of pre-packaged leafy vegetables and 549 samples of green onions were collected and analyzed. HAV was not detected in any of the samples tested, while NoV was detected in 25 samples of leafy vegetables (2.2%) and three samples of green onions (0.5%). Positive results indicate that the products came in contact with the virus at some point of the production and distribution chain, suggesting that Good Agricultural Practices (GAPs) or Good Manufacturing Practices (GMPs) were not followed or appropriately implemented. Immediate follow-up activities were not possible as the types of products examined during this survey had a very short shelf-life and were no longer on the market by the time the results were confirmed. No NoV or HAV outbreaks associated with the consumption of these products were reported during this survey. As current methods for virus detection are molecular-based assays that do not discriminate live, infectious viruses, from dead viruses, it is not possible to determine whether the positive samples were capable of causing illness based on laboratory results alone. It is important to note that food virology is a fairly emerging field, and that there are currently no internationally recognized assessment criteria and harmonized analytical methods for the detection of viruses in fresh produce.

The CFIA regulates and provides oversight to the industry, works with provinces and territories, and promotes safe handling of foods throughout the food production chain. However, 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. 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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