Concurrent outbreaks of Escherichia coli O157:H7 and O157:H39 with high asymptomatic carriage of other Shiga toxin-producing E. coli in nursery children, south-east Scotland, United Kingdom, July to October 2022.

We managed a complex outbreak of Shiga toxin-producing Escherichia coli (STEC) and stx-negative E. coli O157 (non-STEC) cases in four nurseries in two neighbouring towns in south-east Scotland, with epidemiological links through shared management, staff or other visits. There were 57 confirmed cases between July and October 2022. Nurseries voluntarily closed to support outbreak control. Subsequent whole genome sequencing identified two separate, unlinked outbreaks of stx2a-positive E. coli O157:H7 (19 confirmed cases in Nursery 1) and stx-negative E. coli O157:H39 (17 confirmed cases in Nursery 2). Smaller numbers of six additional STEC and E. coli O157 (non-STEC) strains were identified in the four nurseries. Five children from Nursery 1 who tested positive for stx2a-positive E. coli O157:H7 required hospitalisation, one of whom developed haemolytic uraemic syndrome. Children with other STEC and E. coli O157 (non-STEC) strains had few or no symptoms. Overall, five of 19 cases with stx2a subtypes were asymptomatic, compared with seven of nine for stx2f subtypes, and 14 of 25 for stx-negative subtypes. Given the findings in this setting, further information on the prevalence of asymptomatic STEC carriage by strain, age and geography, and in other contexts, will support understanding and risk management of future outbreaks.