Food safety

Surface decontamination of fruits and vegetables eaten raw


Introduction (from report)

Raw fruits and vegetables have been known to serve as vehicles of human disease for at least a century. In 1899, Morse linked typhoid infection to eating celery. Warry (1903) attributed an outbreak of typhoid fever to eating watercress grown in soil fertilized with sewage and Pixley (1913) recorded two cases of typhoid from eating uncooked rhubarb which was grown in soil known to have been fertilized with typhoid excreta. In 1912, Creel demonstrated that lettuce and radishes grown in soil containing Bacillus typhosa (now Salmonella Typhi) harboured the organism on their surfaces for up to 31 days. Melick (1917) recovered typhoid bacilli from mature lettuce and radish harvested from soil that had been inoculated at the time seeds were planted. Some parasitic helminths (e.g. Fasciola hepatica, Fasciolopsis buski) require encystment on plants to complete their life cycle. Thus, the recognition of raw fruits and vegetables as potential vehicles for transmission of pathogenic microorganisms known to cause human disease is not new. Nevertheless, documented outbreaks of foodborne illness associated with fruits and vegetables in industrialized countries are relatively rare. For instance, in 1996 only six of about 200 reported foodborne disease outbreaks in the United Kingdom were associated with consumption of fruits and vegetables (PHLS, 1996). In recent years, however, the frequency of outbreaks epidemiologically associated with raw fruits and vegetables is documented to have increased in some industrialized countries (e.g the United States) as a result of change in dietary habits and increased import of food (Altekruse et al., 1997). In developing countries, foodborne illnesses caused by contaminated fruits and vegetables are frequent and in some areas they cause a large proportion of illness. However, due to lack of foodborne disease investigation and surveillance in most of these countries, most outbreaks go undetected and the scientific literature reports only on very few outbreaks. In 1995-1996, only 2% of foodborne disease outbreaks in Latin America were related to fruits and vegetables (PAHO/INPPAZ, 1996).

Raw and minimally-processed fruits and vegetables are an essential part of peopleís diet all around the world. Where land is available, families grow fruits and vegetables for their own use. Alternatively, produce is purchased from local farmers or retail outlets for further preparation by street vendors, by families at home or as part of meals eaten in restaurants and other food-service facilities. While advances in agronomic practices, processing, preservation, distribution and marketing have enabled the raw fruit and vegetable industry to supply high-quality produce to many consumers all year round, some of these same practices have also expanded the geographical distribution and incidence of human illness associated with an increasing number of pathogenic bacterial, viral and parasitic microorganisms.

Changes that may contribute to the increase in diseases associated with the consumption of raw fruits and vegetables in industrialized countries (Hedberg et al., 1994) and foods in general (Altekruse and Swerdlow, 1996; Altekruse el al., 1997; Potter et al., 1997) have been described. Factors include globalization of the food supply, inadvertent introduction of pathogens into new geographical areas ó e.g. outbreaks of shigellosis in Norway, Sweden and the United Kingdom in 1994 due to contaminated lettuce imported from southern Europe (Frost et al., 1995; Kapperud et al., 1995) and cyclosporiasis in the United States which was linked to consumption of contaminated raspberries imported from Guatemala (Centers for Disease Control and Prevention, 1996c) ó and the development of new virulence factors by microorganisms, decreases in immunity among certain segments of the population, and changes in eating habits. In developing countries, continued use of untreated wastewater and manure as fertilizers for the production offruits and vegetables is a major contributing factor to contamination that causes numerous foodborne disease outbreaks.

While every effort should be made to prevent contamination of fruits and vegetables during production, transport, processing and handling, much improvement is still needed in some parts of the world if hygienic production of fruits and vegetables is to be ensured. Furthermore, many microbial contaminants are part of the environment and fruits and vegetables may be inadvertently contaminated. Unless measures are taken to decontaminate them, their safety may not be assured. This document provides an overview of the hazards associated with fruits and vegetables eaten raw, reviews the methods used for their decontamination (particularly with reference to chemical methods) and evaluates, on the basis of available scientific data, the efficacy of these methods. The purpose of this review is to provide public health authorities with information on the surface decontamination of fruits and vegetables eaten raw, and with guidelines and recommendations that can be provided to growers, processors and consumers.