Calves as a source of an outbreak of cryptosporidiosis among young children in an agricultural closed community.

Transmission of Cryptosporidium from animals to humans, originating mainly in calves, had been suggested previously but has remained unproved. An outbreak of cryptosporidiosis that started among calves was transmitted to multiple pediatric groups living in close contact through one family who had close contact with the calves. Eleven of 19 (58%) infants and young children ages 10 to 15 months had Cryptosporidium compared with 3 of 27 (11%) of those ages 36 to 60 months and none of those ages 16 to 35 months. None of the asymptomatic children was positive for Cryptosporidium. These data emphasize that an extensive human to human transmission does not rule out the zoonotic nature of cryptosporidiosis.