Janet Hughes of Gloucestershire Live writes that scientists are checking to see if summer holiday visits to animal attractions are behind a massive spike in the number of toddlers with cryptosporidium.
Public health chiefs are asking affected families to fill in questionnaires about where they have been and what they have eaten in an effort to trace the source of the outbreak which is particularly bad in Gloucestershire and Wiltshire.
Children aged between one and five years are most at risk from the parasite cryptosporidium which is three or four times more prevalent than normal this summer.
Doctors believe a small number of cases could be linked Oasis leisure centre in Swindon, which has been closed as a precautionary measure, and say swimming in contaminated lakes, rivers or swimming pools can cause the disease to strike.
But many of those struck down are young toddlers so other possible theories include the prospect that children might not have washed their hands after petting animals at attractions during the summer holidays.
Hand washing is never enough.