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Escherichia coli are the most
numerous aerobic commensal inhabitants of the large intestine. Certain
strains produce toxins that cause diarrhea, and all strains produce
infection when they invade sterile tissues. Diagnosis is by standard
culture techniques. Toxin assays may be helpful for diarrhea. Treatment
with antibiotics is guided by sensitivity studies.
E.
coli normally inhabits the GI tract. Enterotoxigenic and enteropathogenic strains are major causes of diarrhea in infants and traveler's diarrhea in adults (see Gastroenteritis: Traveler's Diarrhea). Enterohemorrhagic strains of E. coli, such as type O157:H7 (see Gram-Negative Bacilli: E. coli O157:H7 Infection), produce several cytotoxins, neurotoxins, and enterotoxins, including Shiga toxin, and cause bloody diarrhea, which, in 2 to 7% of cases, may lead to hemolytic-uremic syndrome (see Thrombocytopenia and Platelet Dysfunction: Thrombotic Thrombocytopenic Purpura (TTP) and Hemolytic-Uremic Syndrome (HUS)). Such strains have most often been acquired from undercooked ground beef. Other strains of enteroaggregative E.
coli are emerging as potentially important causes of persistent diarrhea in patients with AIDS and in children in tropical areas.
If normal intestinal anatomic barriers are disrupted (eg, by ischemia, inflammatory bowel disease, trauma), the organism may spread to adjacent structures or invade the bloodstream.
The extraintestinal site most often infected by E. coli is the urinary tract, which is generally colonized by ascending infection from the perineum. Hepatobiliary, peritoneal, cutaneous, and pulmonary infections also oc-cur. E. coli bacteremia may also occur with-out an evident portal of entry. E. coli bacteremia and meningitis are common in newborns, particularly preterm infants (see Infections in Neonates: Neonatal Meningitis; see Infections in Neonates: Neonatal Sepsis).
Samples of blood, stool, or other clinical material are sent for culture. If an enterohemorrhagic strain is suspected, the laboratory must be notified because special culture media are required.
Treatment must be started empirically and then modified on the basis of antibiotic sensitivity studies. Many strains are resistant to ampicillin and tetracyclines, so that other drugs should be used, including ticarcillin , piperacillin , the cephalosporins, aminoglycosides, trimethoprim-sulfamethoxazole (TMP-SMX), and fluoroquinolones. Surgery may be required to drain pus, debride necrotic lesions, or remove foreign bodies.
E. coli O157:H7 Infection
E. coli O157:H7 typically causes
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 controversial.
Epidemiology
Although over 100 serotypes of E. coli produce Shiga and Shiga-like toxins, E. coli O157:H7 is the most common in North America. 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. It can occur in people of all ages, although severe infection is most common in children and the elderly. E. coli O157:H7 has a bovine reservoir, so outbreaks and sporadic cases 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. The organism can also be transmitted (especially among infants in diapers) by the fecal-oral route.
After ingestion, E. coli O157:H7 and similar strains of E. coli (termed enterohemorrhagic E. coli) produce high levels of various toxins in the large intestine that are closely related to the potent cytotoxins produced by Shigella dysenteriae type 1, cholera, and other enteropathogens. 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).
Symptoms and Signs
E.
coli O157:H7 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, may occasionally reach 39° C. Diarrhea may last 1 to 8 days in uncomplicated infections.
About 5% of cases (mostly children < 5 yr and adults > 60 yr) are complicated by the hemolytic-uremic syndrome (see Thrombocytopenia and Platelet Dysfunction: 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.
Diagnosis
E.
coli O157:H7 infection should be distinguished from other infectious diarrheas by isolating the organism from stool cultures. 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. A rapid stool assay for Shiga toxin may help. Patients at risk of noninfectious diarrheas may need sigmoidoscopy. If performed, sigmoidoscopy may reveal erythema and edema; barium enema typically shows evidence of edema with thumbprinting.
Treatment
and Prevention
The mainstay of treatment is supportive. Although E. coli is sensitive to most commonly used antimicrobials, 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 for 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.
Proper 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 E. coli O157:H7 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.
Last full review/revision November 2005
Content last modified November 2005
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