Prevalence and epidemiology of non-O157 Escherichia coli serogroups O26, O103, O111, O145 and Shiga toxin gene carriage in Scottish cattle, 2014-2015.

Cattle are a reservoir for Shiga toxin-producing Escherichia coli (STEC), zoonotic pathogens that cause serious clinical disease. Scotland has a higher incidence of STEC infection in the human population than the European average. The aim of this study was to investigate the prevalence and epidemiology of non-O157 serogroups O26, O103, O111, O145, and Shiga toxin gene carriage, in Scottish cattle. Faecal samples (n = 2783) were collected from 110 herds between 2014-2015 and screened by real-time PCR. Herd-level prevalence (95% CI) for O103, O26 and O145 was estimated as 0.71 (0.62, 0.79), 0.43 (0.34, 0.52) and 0.23 (0.16, 0.32), respectively. Only two herds were positive for O111. Shiga toxin prevalence was high in both herds and pats, particularly for stx2 (herd-level: 0.99, 95% CI: 0.94, 1.0). O26 bacterial strains were isolated from 36 herds on culture. Fifteen herds yielded O26 stx-positive isolates that additionally harboured the intimin gene; six of these herds shed highly pathogenic stx2a-positive strains.Multiple serogroups were detected in herds and pats, with only 25 herds negative for all serogroups. Despite overlap in detection, regional and seasonal effects were observed. Higher herd prevalence for O26, O103 and stx1 occurred in the South West and this region was significant for stx2 at the pat-level (P = 0.015). Significant seasonal variation was observed for O145 prevalence, highest in autumn (P = 0.032). Negative herds were associated with Central Scotland and winter. Herds positive for all serogroups were associated with autumn, larger herd size and were not housed at sampling.IMPORTANCECattle are reservoirs for Shiga toxin Escherichia coli (STEC), bacteria shed in animal faeces. Human are infected through consumption of contaminated food or water, and by direct contact, causing serious disease and kidney failure in the most vulnerable. The contribution of non-O157 serogroups to STEC illness was underestimated for many years, due to the lack of specific tests. Recently non-O157 human cases have increased, with O26 STEC of particular note. It is therefore vital to investigate the level and composition of non-O157 in the cattle reservoir, and compare to historical levels and the clinical situation. In this study we found cattle prevalence high for toxin, as well as O103 and O26 serogroups. Pathogenic O26 STEC were isolated from 14% of study herds, with toxin subtypes similar to that seen in Scottish clinical cases. This study highlights the current risk to public health from non-O157 STEC in Scottish cattle.