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Infection by Escherichia coli O157:H7 and Other Enterohemorrhagic E. coli (EHEC)

by Larry M. Bush, MD, Maria T. Perez, MD

E. coli O157:H7 and other enterohemorrhagic E. coli (EHEC) typically cause acute bloody diarrhea, which may lead to hemolytic-uremic syndrome. Symptoms are abdominal cramps and diarrhea that may be grossly bloody. Fever is not prominent. Diagnosis is by stool culture and toxin assay. Treatment is supportive; antibiotic use is not recommended.

Epidemiology

EHEC include > 100 serotypes that produce Shiga and Shiga-like toxins (Shiga toxin–producing E. coli [STEC]). E. coli O157:H7 is the most common STEC in North America. However, non-O157 STEC serotypes (particularly O26, O45, O91, O103, O111, O113, O121, O128, and O145) may also cause enterohemorrhagic illness, particularly outside the US. In 2011, serotype O104:H4 caused a significant, multinational outbreak in Europe. In some parts of the US and Canada, E. coli O157:H7 infection may be a more common cause of bloody diarrhea than shigellosis or salmonellosis. E. coli O157:H7 infection can occur in people of all ages, although severe infection is most common among children and the elderly.

E. coli O157:H7 and other STEC have a bovine reservoir, so outbreaks and sporadic cases typically occur after ingestion of undercooked beef (especially ground beef) or unpasteurized milk. Food or water contaminated with cow manure or raw ground beef can also transmit infection; in the 2011 European O104:H4 outbreak, infection was transmitted by contaminated raw bean sprouts. The organism can also be transmitted by the fecal-oral route, especially among infants in diapers (eg, via inadequately chlorinated children’s wading pools).

Pathophysiology

After ingestion, E. coli O157:H7 and similar STEC serotypes produce high levels of various toxins in the large intestine; these toxins are closely related to the potent cytotoxins produced by Shigella dysenteriae type 1. These toxins appear to directly damage mucosal cells and vascular endothelial cells in the gut wall. If absorbed, they exert toxic effects on other vascular endothelia (eg, renal).

About 5% of cases (mostly children < 5 yr and adults > 60 yr) are complicated by hemolytic-uremic syndrome (see Thrombotic Thrombocytopenic Purpura (TTP) and Hemolytic-Uremic Syndrome (HUS)), which typically develops in the 2nd wk of illness. Death may occur, especially in the elderly, with or without this complication.

Symptoms and Signs

EHEC infection typically begins acutely with severe abdominal cramps and watery diarrhea that may become grossly bloody within 24 h. Some patients report diarrhea as being “all blood and no stool,” which has given rise to the term hemorrhagic colitis. Fever, usually absent or low grade, occasionally reaches 39° C. Diarrhea may last 1 to 8 days in uncomplicated infections.

Diagnosis

  • Stool cultures

  • Rapid stool assay for Shiga toxin

E. coli O157:H7 and other STEC infections should be distinguished from other infectious diarrheas by isolating the organism from stool cultures. Identifying the specific serotype helps identify the origin of an outbreak. Often, the clinician must specifically ask the laboratory to test for the organism. Because bloody diarrhea and severe abdominal pain without fever suggest various noninfectious etiologies, E. coli O157:H7 infection should be considered in suspected cases of ischemic colitis, intussusception, and inflammatory bowel disease. Characteristically, no inflammatory cells are found in the stool fluid. A rapid stool assay for Shiga toxin or, when available, a test for the gene that encodes the toxin may help.

Patients at risk of noninfectious diarrheas may need sigmoidoscopy. If done, sigmoidoscopy may reveal erythema and edema; barium enema typically shows evidence of edema with thumbprinting.

Treatment

  • Supportive care

The mainstay of treatment is supportive. Although E. coli is sensitive to most commonly used antibiotics, antibiotics have not been shown to alleviate symptoms, reduce carriage of the organism, or prevent hemolytic-uremic syndrome. Fluoroquinolones are suspected of increasing release of enterotoxins.

In the week after infection, patients at high risk of developing hemolytic-uremic syndrome (eg, children < 5 yr, the elderly) should be observed for early signs, such as proteinuria, hematuria, red cell casts, and rising serum creatinine. Edema and hypertension develop later. Patients who develop complications are likely to require intensive care, including dialysis and other specific therapies, at a tertiary medical center.

Prevention

Improved meat processing procedures in the US have helped reduce the rate of meat contamination. Correct disposal of the stool of infected people, good hygiene, and careful hand washing with soap limit spread of infection. Preventive measures that may be effective in the day care setting include grouping children known to be infected with STEC or requiring 2 negative stool cultures before allowing infected children to attend. Pasteurization of milk and thorough cooking of beef prevent food-borne transmission.

Reporting outbreaks of bloody diarrhea to public health authorities is important because intervention can prevent additional infections.

Key Points

  • Enterohemorrhagic E. coli (EHEC) produce Shiga toxin, which causes severe, bloody diarrhea and sometimes hemolytic-uremic syndrome.

  • There are > 100 serotypes of EHEC; O157:H7 is the best-known, but many others cause similar illness.

  • EHEC have a bovine reservoir, so outbreaks often result from ingestion of undercooked beef, but many other foods (eg, fresh produce, raw milk) and sources (eg, direct exposure to animals) may be involved.

  • Use stool tests to identify Shiga toxin and cultures to identify EHEC.

  • Provide supportive care; antibiotics are not helpful.

  • Monitor patients for signs of hemolytic-uremic syndrome for a week or two after onset of illness.

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