In the past two decades, the consumption of fresh fruits and vegetables in the United States has increased, and the geographic sources and distribution of fresh produce have expanded greatly. Concomitantly, public health officials have documented an increase in the number of reported produce-associated foodborne disease outbreaks in the United States. The Centers for Disease Control and Prevention (CDC) reports that the number of these outbreaks doubled between 1973 and 1987, and 1988 and 1991, and that the number of cases of illness associated with these outbreaks more than doubled. A variety of produce items have been affected. During 1995 alone, major outbreak investigations linked infections with Salmonella serotype Stanley to alfalfa sprouts, Salmonella Hartford to unpasteurized orange juice, Shigella spp. to lettuce and green onions, Escherichia coli O157:H7 to lettuce, and hepatitis A virus to tomatoes. In response to this apparent increase, the U.S. Food and Drug Administration asked the National Advisory Committee on Microbiological Criteria for Foods to address and better define the association of foodborne disease and microbial pathogens with fresh produce. A subcommittee formed in June 1995 is documenting relevant epidemiologic data, current industry practices, and laboratory data to identify potential hazards and related control strategies. This report presents the preliminary findings of that subcommittee.

Biochemically atypical strains classified as Vibrio cholerae were characterized by biochemical reactions, serology, antibiotic susceptibility testing, and deoxyribonucleic acid relatedness. Strains with the following atypical reactions were shown to be V. cholerae: mannose negative, mannitol negative, lysine decarboxylase negative, no growth in the presence of 5% NaCI, salicin and cellobiose positive. Sucrose-negative strains were shown to constitute a new species, Vibrio mimicus, whose type strain is 1721-77 (ATCC 33653). In addition to its negative sucrose reaction, V. mimicus was differentiated from V. cholerae by its negative Voges-Proskauer, corn oil, and Jordan tartrate reactions and by its sensitivity to polymyxin. V. mimicus was isolated from shellfish and water, as well as from human diarrheal stools and ear infections. Most strains were typable with antisera against V. cholerae. Strains from three serogroups produced either a heat-labile or a heat-stable enterotoxin.

The isolation rate for Salmonella enterica serotype Enteritidis (SE) in humans in the United States of America (USA) increased from 1,207 sporadic isolates identified in 1976 (0.6 isolates/100,000 population) to 10,201 identified in 1995 (4.0/100,000 population). The proportion of reported Salmonella isolates which were SE increased from 5% to 25% during the same time period. In 1990,1994, and 1995, SE was the most commonly reported Salmonella serotype in the USA. Much of this increase has been associated with the consumption of contaminated shell eggs. An examination of the results of a United States Department of Agriculture (USDA) survey of spent hens at slaughter and unpasteurised liquid egg at breaker plants (liquid egg processors) in 1991 and 1995 reveals an increase in the prevalence of SE isolates overall and in most regions of the USA. SE phage type 4 (pt 4), the predominant SE phage type in other parts of the world, has emerged in the egg industry in the western USA concurrent with a sharp increase in the number of sporadic human SE pt 4 isolates in California and Utah. Research on the molecular structure and virulence of SE pt 4 isolates from the USA as compared with isolates from other parts of the world (human and poultry) should be a priority. A comparison of DNA from pt 4 isolates from the USA and Europe may provide information about the potential threat to public health and poultry in the USA from this phage type. Some regional success in the reduction of human illness as a result of SE control efforts is apparent. The Pennsylvania Egg Quality Assurance Program has shown progress in reducing SE infection in participating flocks. At a national level, however, neither the incidence of human illness due to SE nor the prevalence of Rev. sci. tech. Off. int. Epiz., 16 (2) 543 SE in flocks and unpasteurised liquid eggs have decreased significantly, despite the Implementation of the USDA 'trace back' regulation from 1990 to 1995, and intensified efforts to educate food handlers and to enforce safe food handling practices. More effort is needed to control SE at every stage of the egg continuum, from production through to consumption. A risk-reduction approach, with barriers to the introduction and multiplication of the pathogen throughout the farm-to-table continuum, is the most practical method for reducing human illness from SE in shell eggs at present. An effective long-term solution will require interdisciplinary efforts involving government, industry, consumers, and academics. Interventions should be developed and evaluated in compliance with the potential for reducing the risk to human health and cost-effectiveness.

The potential for microbial contamination of fruits and vegetables is high because of the wide variety of conditions to which the produce is exposed during growth, harvest, and distribution. Heat treatment may also destroy the protective barriers (peels, husks, rinds) of fruits and vegetables, permitting the entry of microbial pathogens into the produce and providing them access to nutrients essential for their growth and proliferation. Proper refrigeration, storage, and shipping conditions as well as removal of soil from fresh produce by washing with chlorinated water are recommended to prevent contamination.