Purpose: Laboratory findings from PulseNet and the National Escherichia coli Reference Laboratory (NRL) were combined to develop a comprehensive profile of STEC strains isolated from humans between 2006 and 2012 in the US.
Methods: Data in PulseNet were used to determine the number of isolates and virulence profiles for STEC O157, O26, O103, O111, O45, O121 and O145, and data from NRL were used to determine these values for all other STEC serogroups. Shiga toxin profiles were determined by EIA or PCR assays and eae and ehxA genes were determined by PCR assays.
Results: A total of 29,869 STEC strains were isolated and characterized during the study period. Ninety-one percent (27,201) expressed or were indistinguishable by PFGE to known patterns for one of the following O antigens: O157 (18,391), O26 (2,767), O103 (2,390), O111 (1,842), O45 (359), O121 (620) and O145 (501), while 9% (2668) expressed one of 125 other O antigens. The percentages of strains in the common O groups that were positive for stx1/stx2/stx1+stx2, respectively, were as follows: O157: 2/56/42; O26: 94/2/4; O103: 97/<1/2; O111: 70/1/29; O45: 95/<1/4; O121: 5/94/1; O145: 30/54/16. Over 99% and 94% of these strains were positive for eae and ehxA, respectively. Among strains from the less common serogroups, stx2 alone or in combination with stx1 was present in 38% of strains, and 53% and 77% of strains were positive for eae and ehxA, respectively.
Significance: Greater than 90% of STEC causing human illness likely belong to 7 serogroups. A small percentage (~3%) of diverse strains with the potential to cause severe disease falls outside these groups. Continued surveillance is important to monitor changes in STEC prevalence.