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Quick Reference Environment:
rare serotype; intestinal tract of cattle Identification Escherichia coli is a Gram-negative anaerobe named for the Austrian doctor, Theodor von Escherich, who first isolated the genus in the family Enterobacteriacae. E. coli are part of the normal intestinal flora of all animals, including humans. The serotype designated E. coli 0157:H7 is a virulent enterohemorrhagic (EHEC) strain. Though identified as a human pathogen shortly after its discovery in 1982, E. coli 0157:H7 has become major foodborne pathogen during the last decade. In the United States, the impact of this serotype on the young and elderly has generated public health concerns and tremendously impacted the beef industry as well as federal agencies that regulate food safety. Pathogenesis This rare serotype produces copious quantities of two potent enterocytotoxins, verotoxin (VT) and shiga-like toxin, similar to the toxin produced by Shigella dysenteriae, that causes severe damage to the intestinal lining and internal organs. Virulence factors:
These toxins adhere to the intestinal epithelium and inhibit protein synthesis, which interferes with cellular repair mechanisms. Red blood cells are damaged as they pass through the altered vasculature. As few as ten cells have been shown to cause disease. Manifestations The incubation period is usually about three days, but symptoms can appear as early as one day or up to nine days following infection. Symptoms can vary wildly, but generally include abdominal cramping, severe watery diarrhea, which may become grossly bloody, and little or no fever. In many cases the condition resolves itself in 5-10 days without treatment. As much as 15% of hemorrhagic colitis cases develop a severe illness known as hemolytic uremic syndrome (HUS). In the elderly, HUS, compounded with other symptoms, constitutes thrombotic thrombocytopenic purpura (TTP), which results in death in as many of 50% of cases. Treatment A stool culture test specific for this serotype is recommended for all patients exhibiting bloody diarrhea. The culture test for E. coli 0157:H7 must be prepared on sorbitol-MacConkey (SMAC) agar and will confirm the presence or absence of E. coli 0157:H7. Recent studies suggest that antibiotics should not be used in the treatment of E. coli 0157:H7 infections due to increased risk of kidney complications. Antidiarrheal medications, such as loperamide, should also be avoided. Blood transfusions and kidney dialysis are often required for those who develop HUS. A lengthy hospital stay is usually necessary. With intensive hospital care and treatment, death occurs in 3-5% of HUS cases. Long-term complications of about one third of HUS cases include abnormal kidney function requiring long-term dialysis. Approximately 8% of remaining patients have additional complications, including high blood pressure, seizures, blindness, paralysis, and partial bowel removal. Prevention As long as E. coli O157:H7 continues to contaminate meat, it will be a public health concern. Research into preventative measures are currently being conducted. Since infection commonly occurs after consuming inadequately cooked ground beef products, ensure that the meat is fully cooked to 160 degrees Fahrenheit. Drink only pasteurized milk and fruit juices. To avoid cross-contamination, keep all uncooked beef products away from foods that do not require cooking and thoroughly wash all utensils that have come in contact with raw meat. Proper sanitary practices and hand washing reduces the possibility of cross-contamination and fecal-oral infection. It is only after the muscle (meat) of cattle comes into contact with the intestinal contents of or feces that the meat becomes contaminated. Rigorous enforcement of sanitary practices in slaughter houses needs to be enacted to improve the safety of the food supply in the United States. Only a minute amount of bacteria is needed to cause infection. Today, HUS is the leading cause of acute renal failure in children. The USDA believes that rates of E. coli 0157:H7 poisoning are rising. |
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