E. coli that are responsible for the numerous reports of contaminated foods and beverages are those that produce Shiga toxin, so called because the toxin is virtually identical to that produced by Shigella dysenteria type 1. The best-known and most notorious E. coli bacteria that produce Shiga toxin is E. coli O157:H7. The Centers for Disease Control and Prevention (CDC) has estimated that every year at least 2,000 Americans are hospitalized, and about 60 die because of E. coli infection and its complications.
E. coli O157:H7 bacteria and other pathogenic E. coli mostly live in the intestines of cattle, but E. coli bacteria have also been found in the intestines of chickens, deer, sheep, and pigs. A 2003 study on the prevalence of E. coli O157:H7 in livestock at 29 county and three large state agricultural fairs in the United States found that E. coli O157:H7 could be isolated from 13.8% of beef cattle, 5.9% of dairy cattle, 3.6% of pigs, 5.2% of sheep, and 2.8% of goats. Over 7% of pest fly pools also tested positive for E. coli O157:H7. Shiga toxin-producing E. coli does not make the animals that carry it ill. The animals are merely the reservoir for the bacteria which can contaminate not only meat products, but also the environment, leading to contamination of food items, like sprouts and leafy greens.
What makes E. coli O157:H7 remarkably dangerous is its very low infectious dose, and how relatively difficult it is to kill these bacteria. “E. coli O157:H7 in ground beef that is only slightly undercooked can result in infection.” As few as 20 organisms may be sufficient to infect a person and, as a result, possibly kill them. And unlike generic E. coli, the O157:H7 serotype multiplies at temperatures up to 44° Fahrenheit, survives freezing and thawing, is heat-resistant, grows at temperatures up to 111 F, resists drying, and can survive exposure to acidic environments. And, finally, to make it even more of a threat, E. coli O157:H7 bacteria are easily transmitted by person-to-person contact.