E coli causes gastroenteritis by a variety of mechanisms. Enterotoxigenic E coli (ETEC) elaborates either a heat-stable or heat-labile toxin that mediates the disease. ETEC is an important cause of traveler’s diarrhea. Enteroinvasive E coli (EIEC) differs from other E coli bowel pathogens in that these strains invade cells, causing bloody diarrhea and dysentery similar to infection with Shigella species. EIEC is uncommon in the United States. Neither ETEC nor EIEC strains are routinely isolated and identified from stool cultures because there is no selective medium. Antimicrobial therapy against Salmonella and Shigella, such as ciprofloxacin 500 mg orally twice daily, shortens the clinical course, but the disease is self-limited.
Shiga-toxin–producing E coli (STEC) infection can result in asymptomatic carrier stage, nonbloody diarrhea, hemorrhagic colitis, hemolytic-uremic syndrome, or thrombotic thrombocytopenic purpura. Although E coli O157:H7 is responsible for most cases of STEC infection in the United States, other STEC strains that cause severe disease (such as E coli O104:H4) have been reported in Europe. E coli O157:H7 has caused several outbreaks of diarrhea and hemolytic-uremic syndrome related to consumption of undercooked hamburger, raw flour, unpasteurized apple juice, and spinach, while E coli O145 was linked to the consumption of contaminated lettuce. Older individuals and young children are most affected, with hemolytic-uremic syndrome being more common in the latter group. STEC identification can be difficult and the CDC recommends that all stools submitted for routine testing from patients with acute community-acquired diarrhea be simultaneously cultured for E coli O157:H7 and tested with an assay that detects Shiga toxins to detect non-O157 STEC, such as E coli O145. Antimicrobial therapy does not alter the course of the disease and may increase the risk of hemolytic-uremic syndrome. Treatment is primarily supportive. Hemolytic-uremic syndrome or thrombotic thrombocytopenic purpura occurring in association with a diarrheal illness suggests the diagnosis and should prompt evaluation for STEC. Confirmed infections should be reported to public health officials.
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