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Chapter 12 : Shiga Toxin-Producing Escherichia coli in Fresh Produce: A Food Safety Dilemma
The worldwide trends for healthier lifestyles to reduce obesity and other complications arising from unhealthy diets have greatly increased the consumption of fresh fruits and vegetables. This increased demand, coupled with ever busier consumer lifestyles, also stimulated the growth of a “convenience” food industry and popularized the concept of bagged salad vegetables and fruits. It has been estimated that several millions of bags of fresh produce are sold daily in the United States. Bagged produce, also referred to as “fresh cut” or “precut,” is often regarded as ready-to-eat (RTE) and consumed without further intervention steps. However, because produce is predominantly cultivated in soil in open fields, it is susceptible to contamination and can contain high levels of complex microbial populations, occasionally including bacterial pathogens. As a result, increases in fresh produce demand and consumption coupled with changes in production practices have also contributed to increases in incidents of food-borne illness. In the United States, about 0.7% of the infections in the 1970s were attributed to fresh produce, but this increased to 6% in the 1990s ( 1 ). Since “fresh cut” products are often mass produced, broadly distributed, and marketed worldwide, a single pathogen contamination event can have broadly impacting consequences, and several large, produce-related outbreaks have occurred in many countries ( 2 , 3 ). In 2006, a large multistate outbreak in the United States that infected more than 200 persons was traced to bagged spinach contaminated with Escherichia coli O157:H7 ( 4 ). Several months later, another O157:H7 outbreak in a fast-food restaurant chain had initially implicated green onions but appeared to have been due to bagged lettuce. At about the same time, bagged lettuce was implicated in another O157:H7 outbreak that affected three states ( 5 ). Likewise, increased consumption of sprouts caused several outbreaks of Salmonella sp., E. coli O157:H7, and other Shigatoxin-producing E. coli (STEC) strains. STEC serotype O26:H11 strains caused an outbreak with alfalfa sprouts and, more recently, with clover sprouts, and the large outbreak of O104:H4 in 2011 in the European Union also implicated the consumption of sprouts ( 6 ). These large produce-related outbreak incidents worldwide have greatly raised concerns about the safety of fresh produce and about the microbiological and sanitary quality of fresh produce.