Cryptosporidiosis: sources of infection and guidelines for prevention.

Cryptosporidium parvum is an important emerging pathogen in the United States and a cause of severe, life-threatening disease in patients with AIDS. No safe and effective form of specific treatment for cryptosporidiosis has been identified to date. The parasite is transmitted by ingestion of oocysts excreted in the feces of infected humans or animals. The infection can therefore be transmitted from person to person through ingestion of contaminated water (drinking water and water used for recreational purposes) or food, from animal to person, or by contact with fecally contaminated environmental surfaces. Outbreaks associated with all of these modes of transmission have been documented. Patients with human immunodeficiency virus infection should be made more aware of the many ways that Cryptosporidium species are transmitted, and they should be given guidance on how to reduce the risk of exposure. This article summarizes existing data on the various modes of transmission. It includes an in-depth look at waterborne transmission because as more research data are made available to the public, physicians will increasingly be asked by patients about the importance of this source of infection compared with other sources of infection.