Normally E. coli serves a useful function in the body by suppressing the growth of harmful bacterial species and by synthesizing appreciable amounts of vitamins. There are several strains of E. coli . The illness is characterized by severe cramping or abdominal pain and diarrhea which is initially watery but can become grossly bloody. Occasionally vomiting occurs. The illness lasts for an average of 8 days.
Outbreaks can be either foodborne or waterborne.
Many E. coli illness outbreaks have been traced to undercooked ground beef, some to unpasteurized milk, and others to water, cider, and vegetables. Dairy farms have been identified as reservoirs of E. coli . In one study, E. coli were found present in quite a few herds but only a small number of animals excreted the organisms which seem to grow in adverse environments. Gastrointestinal tracts of well-fed cattle were less conducive to growth of E. coli than cattle deprived of feed. These bacteria are probably killed by pasteurization.