Because the annual incidence rate of Escherichia coli O157 infection in 2008—an unexceptional year—was 2.9 per 100 000 population in the United Kingdom,1 most clinicians will rarely see a case of infection with this or any other serotype of verotoxigenic E coli. It is vital, however, that they—and particularly general practitioners—have a low threshold for suspecting E coli O157 infection, because it can cause serious complications and large outbreaks, as highlighted by recent incidents involving visitors to open farms (www.bmj.com/cgi/content/extract/339/sep15_2/b3795). Such outbreaks also exemplify the difficulties of controlling sources of infection, and the importance of general practitioners in promptly reporting suspected cases, and in preventing both serious sequelae and secondary spread.

The low infectious dose of E coli O157—probably fewer than 1000 organisms—increases the risk of large outbreaks, and secondary spread, which causes 6-17% of all cases and up to 31% of outbreak cases.2 Bloody diarrhoea occurs in up to 90% of cases, …