Ten-year trends and risk factors for non-O157 Shiga toxin-producing Escherichia coli found through Shiga toxin testing, Connecticut, 2000-2009

Abstract

Background: The epidemiology over time of non-O157 Shiga toxin-producing Escherichia coli (STEC) is unknown. Since 1999, increasing numbers of laboratories in Connecticut have been testing for ST rather than culturing for O157, enabling identification of non-O157 STEC.

Methods: Beginning in 2000, Connecticut laboratories were required to submit ST-positive broths to the State Laboratory for isolation and typing of STEC. The ratio of non-O157:O157 from laboratories conducting ST testing was used to determine state-level estimates for non-O157 STEC. Patients with STEC were interviewed for exposure factors in the 7 days preceding illness. Incidence trends, clinical features, and epidemiology of non-O157 and O157 STEC infections were compared.

Results: From 1 January 2000 through 31 December 2009, ST testing detected 392 (59%) of 663 reported STEC infections; 229 (58%) of the isolates were non-O157. The estimated incidence of STEC infection decreased by 34%. O157 and the top 4 non-O157 serogroups, O111, O103, O26, and O45, were a stable percentage of all STEC isolates over the 10-year period. Bloody diarrhea, hospitalization, and hemolytic uremic syndrome were more common in patients with O157 STEC than in patients with non-O157 STEC infection. Exposure risks of patients with non-O157 STEC infection differed from those of patients with O157 STEC infection primarily in international travel (15.3% vs 2.5%; P < .01). Non-O157 types differed from each other with respect to several epidemiologic and exposure features.

Conclusions: Both O157 and non-O157 STEC infection incidence decreased from 2000 through 2009. Although infection due to O157 is the most common and clinically severe STEC infection, it accounts for a minority of all clinically significant STEC infections. STEC appear to be a diverse group of organisms that have some differences as well as many epidemiologic and exposure features in common.