Enteric illness outbreaks among middle-/high-school students in consecutive semesters of an educational farm programme were investigated with retrospective cohort studies. During the first outbreak, 31/92 (34%) interviewed students were ill. Risk factors included participating in animal science class (RR 8.1, 95% CI 1.2-55.2) and contact with calves (RR 4.2, 95% CI 1.1-16.2). Stool samples from seven students and two calves yielded Cryptosporidium parvum. Students cared for animals in street clothes and practised poor hand washing. During the second outbreak, 37/81 (46%) interviewed animal science students were ill. Risk factors included having visible manure on hands, and wearing coveralls and boots. Stool samples from seven students and eight calves yielded C. parvum. Student hand washing was still inadequate. Coveralls/boots were cleaned infrequently and removed after hand washing. These outbreaks of cryptosporidiosis resulted from calf contact and inadequate hygiene practices. The failure to adequately implement recommended interventions contributed to the second outbreak.

• U50/CCU511190/PHS HHS/United States