Recent major outbreaks of foodborne illness continue to heighten our awareness about the complexity of the farm-to-fork continuum and the relevance of the on-farm or preharvest role. For example, outbreaks of Cyclospora in Guatemalan raspberries, hepatitis A from Mexican green onions and norovirus from British Columbian oysters all began with contamination at the preharvest level. For many food products, it can be difficult to prevent transmission of pathogens to consumers once the food leaves the farm, since postharvest decontamination steps, if available, are not always effective. For food products eaten raw, like fruits, vegetables, nuts and some seafood, there is no cooking process to inactivate pathogens. Another complication can be home preparation where raw food products, like meat, can be the source of pathogens to other items in the food preparation environment before cooking. There are many steps in the process that brings food from the farm to the table; each step provides opportunities for contamination and, ultimately, risk of foodborne illness. This colloquium only considered preharvest food safety, although we recognized that it is not the only or, in some case, the most critical, stage of food production. However, cost effective interventions with the potential of reducing levels of contamination can be useful in the continuum of food production.
Outside of basic hygiene practices, few food safety controls are in place in food production environments (preharvest) because not enough information is available on what would control foodborne pathogens. There are multiple needs for data: systematic surveillance would provide baseline data on the prevalence of pathogens, and epidemiologic research could help identify effective controls. Comprehensive and transparent risk assessments on preharvest issues are needed to continue to identify risk mitigation priorities and to provide comparisons among intervention strategies.
The human pathogens of concern in preharvest environments include a wide array of viruses, parasites, and bacteria that can have a range of effects and severity, depending on pathogen-specific and hostspecific properties. Due to differences in cultivation practices and wealth of resources, the organisms of concern on farms in industrialized nations and in developing countries are likely to be quite different.
Admittedly, eliminating pathogens from the preharvest environment would be nearly impossible. A more practical goal for preharvest food safety interventions is to reduce pathogen numbers to levels that will reduce the degree of hazard to public health. Unfortunately, since there is not always a definitive link between preharvest food safety and public health, and there are many factors in between, it will first be important to understand the role of preharvest contamination and control strategies on the overall burden of microbes in our food supply. This is complicated because some foods are marketed direct from the farm to retail (produce), while other products have intermediate processing steps (meats), and their impacts on importance of on-farm measures may be different. Furthermore, this may afford only temporary success, since the pathogens may reproduce and disseminate during other steps in the farm-to-fork continuum. Indeed, many factors play roles in determining the numbers of pathogens in food production environments, including diet, seasonal factors, and microbial symbioses, among others.
In light of global concerns about bioterrorism, biological security on the farm is an even bigger concern. A number of security-sensitive points in food production processes were discussed, and priorities for security measures were identified.
Although progress has been made, our understanding of the epidemiology of foodborne pathogens on the farm and the best ways to manage their risks is limited at best. A number of specific preharvest food safety research needs were identified, including validation and development of interventions, development of better tools for pathogen detection and enumeration, and investigation of the effects of interventions on microbial community dynamics.
Richard E. Isaacson, Mary Torrence, Merry Buckley. 2005. Preharvest food safety and security.
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