Background: Escherichia coli O157:H7 is increasingly recognized as a cause of bacterial diarrhea in the United States, but the frequency of its isolation and the clinical and epidemiologic features of E. coli O157:H7 infection in a large, geographically diverse population of patients have not been well described.
Objective: To determine the frequency of isolation of E. coli O157:H7 relative to that of other bacterial enteric pathogens in a nationwide sample of patients and to identify the clinical and epidemiologic features of E. coli O157:H7 infection.
Design: Population prevalence study from October 1990 to October 1992.
Setting: 10 U.S. hospitals.
Patients: Both inpatients and outpatients who had stool samples submitted to 1 of 10 laboratories for routine pathogen identification.
Measurements: Clinical, epidemiologic, and laboratory information was collected for infected and uninfected patients. Isolates of E. coli O157:H7 were tested for production of Shiga toxin. Patient charts were then reviewed.
Results: Escherichia coli O157:H7 was isolated from 118 (0.39%) of the 30463 fecal specimens tested. The proportion of fecal specimens with isolates was higher at northern sites (0.57%) than at southern sites (0.13%) (P < 0.001). Escherichia coli O157:H7 was more likely to be isolated from visibly bloody stool specimens than from specimens without visible blood (odds ratio [OR], 59.2 [95% CI, 36.6 to 96.0) and was the pathogen most commonly isolated from visibly bloody stool specimens that yielded a bacterial enteric pathogen (39% of such specimens). The highest age-specific isolation proportions from fecal specimens for E. coli O157:H7 were in patients 5 to 9 years of age (0.90%) and 50 to 59 years of age (0.89%). Clinical features independently associated with E. coli O157:H7 infection compared with the other enteric pathogens included a history of bloody diarrhea (OR, 18.6 [CI, 7.4 to 48.6]), visibly bloody stool specimens (OR, 8.1 [CI, 3.6 to 18.3]), no reported fever (OR, 8.3 [CI, 1.6 to 50.0]), leukocyte count greater than 10 x 10(9)/L (OR, 4.0 [CI, 1.7 to 9.5]), and abdominal tenderness on physical examination (OR, 2.9 [CI, 1.2 to 7.2]).
Conclusions: In some geographic areas and some age groups, isolation proportions from fecal specimens for E. coli O157:H7 surpassed those of other common enteric pathogens. One third of isolates of this organism came from nonbloody specimens. Because person-to-person transmission of E. coli O157:H7 is not uncommon and infection with this organism may cause severe disease, stool specimens from all patients with a history of acute bloody diarrhea should be cultured for E. coli O157:H7.