Children with gastrointestinal infections caused by Escherichia coli O157:H7 are at risk for the hemolytic–uremic syndrome. Whether antibiotics alter this risk is unknown.

We conducted a prospective cohort study of 71 children younger than 10 years of age who had diarrhea caused by E. coli O157:H7 to assess whether antibiotic treatment in these children affects the risk of the hemolytic–uremic syndrome and to assess the influence of confounding factors on this outcome. Estimates of relative risks were adjusted for possible confounding effects with the use of logistic-regression analysis.

Among the 71 children, 9 (13 percent) received antibiotics and the hemolytic–uremic syndrome developed in 10 (14 percent). Five of these 10 children had received antibiotics. Factors significantly associated with the hemolytic–uremic syndrome were a higher initial white-cell count (relative risk, 1.3; 95 percent confidence interval, 1.1 to 1.5), evaluation with stool culture soon after the onset of illness (relative risk, 0.3; 95 percent confidence interval, 0.2 to 0.8), and treatment with antibiotics (relative risk, 14.3; 95 percent confidence interval, 2.9 to 70.7). The clinical and laboratory characteristics of the 9 children who received antibiotics and the 62 who did not receive antibiotics were similar. In a multivariate analysis that was adjusted for the initial white-cell count and the day of illness on which stool was obtained for culture, antibiotic administration remained a risk factor for the development of the hemolytic–uremic syndrome (relative risk, 17.3; 95 percent confidence interval, 2.2 to 137).

Antibiotic treatment of children with E. coli O157:H7 infection increases the risk of the hemolytic–uremic syndrome.