Emerging Infectious Diseases

Disease caused by Shiga toxin-producing Escherichia coli (STEC) ranges from self-limiting diarrhea to hemorrhagic colitis and hemolytic uremic syndrome (HUS). Serotype O157:H7, the most frequently implicated STEC causing hemorrhagic colitis and HUS, has been isolated from large foodborne outbreaks, as well as sporadic cases, in North America and abroad. However, 60 STEC serotypes have been implicated in diarrheal disease, and several non-O157:H7 serotypes have been implicated as the cause of foodborne outbreaks and HUS in the United States, Europe, and Australia. Studies from Canada, Europe, Argentina, and Australia suggest that nonO157:H7 STEC infections are as prevalent, or more so, than O157:H7 infections. E. coli O157:H7 is easily differentiated from other E. coli by its inability to rapidly ferment sorbitol; however, non-O157:H7 STEC are phenotypically similar to commensal nonpathogenic E. coli and are not detected with sorbitol MacConkey agar. To detect non-O157:H7 STEC, nonculture methods are used (enzyme immunoassay [EIA] or polymerase chain reaction [PCR]), which are typically only performed in reference laboratories. The purpose of this study was to determine the prevalence of non-O157:H7 STEC in persons with diarrhea in Nebraska. The Study Nine regional clinical microbiology laboratories in Nebraska sent stool samples from March 1, 1998, to October 31, 1998, to the Nebraska Public Health Laboratory, University of Nebraska Medical Center. All stool samples that were sent to a participating laboratory with a physician’s order to screen for enteric pathogens were included. Thus, all samples were from patients with a differential diagnosis of bacterial gastroenteritis. Patients who had been in the hospital for >2 days before diarrhea developed were excluded. The samples were added to a Para-Pak C&S stool transport container (Meridian Diagnostics, Cincinnati, OH) and sent by courier to the Nebraska Public Health Laboratory. Samples were plated to cefixime-tellurite sorbitol MacConkey (CT-SMAC) agar plates and screened for typical sorbitol-negative colonies (1). Presumptive colonies were identified as E. coli by API strips (Biomerieux Vitek, Hazelwood, MO) and serotyped with RIM E. coli O157:H7 (Remel, Lenexa, KS). Samples were injected into 10 mL MacConkey broth (Difco, Detroit, MI) and incubated overnight at 37°C. The Premier enterohemorrhagic E. coli (EHEC) assay was performed by using 50 μL of overnight growth. The reaction mixtures were read spectrophotometrically at 450 nm and scored as positive or negative. PCR was performed by first extracting DNA from the overnight culture of MacConkey broth using a QIAamp Tissue kit (Qiagen, Santa Prevalence of Non-O157:H7 Shiga Toxin-Producing Escherichia coli in Diarrheal Stool Samples from Nebraska