Abstract
Because consumers have developed a better understanding of the health benefits associated with eating fresh produce, salads are increasingly being served in the home, in restaurants and as ready-to-eat pre-packaged foods. The associated increase in food-borne diseases must be seen in view of these benefits. Bacterial pathogens can survive on growing plants over prolonged periods of time under field conditions. In addition, the ability of human pathogens to infiltrate plant tissues has been recognized recently. Prepackaged, precut lettuce (i.e. damaged plant tissue) may pose a risk as an emerging source of food-borne illness. Surprisingly, there are no clear differences in pathogen contamination reported between organically grown produce and conventionally grown produce. The present intervention strategies are inadequate to ensure by 100% that salads are not contaminated with food-borne bacterial pathogens. The relative infrequency of outbreaks associated with preharvest contamination with Shigella, an organism with humans as its major reservoir, and the relative frequency of those associated with Salmonella or Shiga toxin-producing Escherichia coli, organisms with animals as their major reservoirs, underline the role of domestic and wild animals as dominant sources of preharvest contamination of vegetable salads. In the overwhelming majority of reported outbreaks, the contamination of salads did not occur before harvest nor did it originate at the processing plants, but rather the source could be traced to symptomatic or asymptomatic food handlers. Thorough epidemiological and microbiological investigation of all food-borne outbreaks is essential to finally assess the importance of preharvest contamination of salads.