Background : Non-O157 human isolates among enterohemorrhagic Escherichia coli (EHEC) serogroup have been reported with increasing frequency in recent years; the serotype O26 is the most common among the non-O157 isolates. We performed serotyping of E. coli isolates with O157, O26, and O111 antisera at Ulsan University Hospital and identified 27 isolates of O26. The purpose of this study was to investigate the clinical significance of E. coli O26 isolates.

Methods : During the 24-month period from January 2002 to December 2003, E. coli isolates were serotyped when requested by the physician because of bloody diarrhea or when blood was noted in the stool specimen at the laboratory. The isolates were identified biochemically by Vitek 1 (BioMerieux Vitek Inc., Mo., USA) and serotyped using diagnostic antisera of O157, O26, and O111 (NIH, Korea). When a positive agglutination reaction was shown, the patient’s was reviewed retrospectively.

Results : Of 4,921 isolates of E. coli during the 2-year period, 200 isolates were serotyped and 27 (13.5%) were identified as serotype O26. These were isolated from stool (13 isolates), urine (9), pus (1), blood (1), and bile (1). Among the 13 patients whose stool specimens grew E. coli O26, 12 had watery diarrhea and 7 bloody diarrhea; two patients had thrombocytopenia and purpura simultaneously. Two patients with watey diarrhea, two with bloody diarrhea, and one with TTP were among the 7 patients with E. coli O26 in the urine. Finally, one patient each with blood isolate and bile isolate of E. coli O26 both had acute gastroenteritis.

Conclusions : Most of the patients infected with E. coli  O26 had clinical manifestations consistent with EHEC infections. E. coli  isolates from patients with boody diarrhea should be serotyped with O157 and O26 antisera. (Korean J Clin Microbiol 2004;7(2):130-134)