Cryptosporidiosis outbreak associated with an educational farm holiday.

In April 1995 an outbreak of cryptosporidiosis occurred among 43 schoolchildren and four staff after a week's holiday at a rural farm. A retrospective cohort study found illness to be 3.8 times more likely in those who handled calves and 1.5 times more likely in those who habitually bit their nails or sucked their thumbs. Cryptosporidium oocysts were detected in faecal specimens from six of the 29 pupils and one of the four staff who were ill. Infection occurred in children despite supervised handwashing. The infection hazards of farm visits need more publicity, and further study on the risks of cryptosporidiosis transmission in the farm environment is required to guide preventive measures.