Introduction. Escherichia coli is a common cause of acute diarrhea mainly in young children and, less frequently, in elderly or immunosuppressed patients. Many types of E. coli are part of the normal enteric flora, but can cause urinary tract or nervous system infections. Objective. To study the prevalence of the main types and serogroups of diarrheagenic E. coli among hospitalized children with enteric infections. Material and methods. Over a period of 5 years, 1,160 hospitalized children with

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... acute diarrhea syndrome were studied. Fecal samples underwent culturing, biochemical and phenotypic identification. Results. Among the studied patients, 112/1,160 children (9.7%) had diarrhea caused by E. coli, and only 4 of the isolates were lactose-negative. The most common was diarrhea caused by ETEC – 65/112 (58.0%), followed by EPEC – 38/112 (33.9%), and in third place – EHES 9/112 (8.0%). We did not isolate EIEC types. Depending on the group of E. coli, we observed some differences in the clinical presentation and specifics in the distribution of patients by age. Conclusion. The study shows that this causative agent is common among Bulgarian children with diarrhea. Unfortunately, in Bulgaria the microbiological network is still not able to adequately respond to the challenges of the extended serodiagnosis for detection of diarrheagenic E. coli, which is performed in Western Europe and North America.