Cases of cryptosporidium are almost four times higher than last year across parts of the U.K., with 267 sick, prompting an investigation by the Health Protection Agency.

A possible source of infection has not been identified although the distribution of cases suggests it is unlikely that public water supplies are implicated.

The majority of people who became unwell are known to be adults with slightly more females than males affected. Most people affected had a mild to moderate form of illness but a small number of people were hospitalised – all have now recovered.

A ‘handful’ of people have been admitted to hospital and have now recovered, a spokesman for the HPA said.

In April, Canadian officials warned that parsley had become contaminated with cryptosporidium, although no one was sick.