Evaluation of colony-based examinations of diarrheagenic Escherichia coli in stool specimens:: low probability of detection because of low concentrations, particularly during the early stage of gastroenteritis

To evaluate traditional colony-based examinations of diarrheagenic Escherichia coli (DEC), we analyzed the proportions of 5 categories of DEC among E. coli in stool specimens from patients with gastroenteritis using real-time polymerase chain reaction with novel primers and probes. Among 81 DEC isolates, 48 (59.3 %) were present at proportions of <= 10 %, whereas only 17 (21.0 %) reached > 50 %. Low concentrations (<= 10 %) of DEC were found, particularly in most (71.8 %) stool specimens collected within 48 h after the onset of illness, although such specimens were conventionally collected as close to the time of diarrhea onset as possible. Because the probability of detecting <= 10 % DEC by colony-based examinations is very low, traditional laboratory methods might not detect most DEC infections, especially at the start of gastroenteritis. Thus, a diagnosis of DEC infections requires a molecular method that targets not individual colonies but E. coli clusters. (c) 2007 Elsevier Inc. All rights reserved.