Some persons infected with Cryptosporidium may not become ill. All persons are presumed susceptible to infection with Cryptosporidium. In most healthy persons with normal immune systems, signs and symptoms generally persist for two weeks or less, although they may improve and then worsen during that time period. However, immune compromised persons may be unable to clear the parasite and may have much more severe and long lasting illness. Cryptosporidium is shed in the feces of infected humans, domestic animals, and wild animals.
Infection occurs when the organism is subsequently ingested by a person.
It may only require a few microscopic Cryptosporidium organisms to infect a person. Thus, cryptosporidiosis can be acquired by person to person or animal to person transmission and by drinking contaminated water. Infected individuals can shed the organism in stool for several weeks after they recover from the illness. Because cryptosporidiosis is transmitted by the fecal-oral route, persons with the greatest potential to transmit the organism include infected persons who have diarrhea, persons who are incontinent of stool, persons with poor personal hygiene, and diapered children. The degree to which a previously infected person is immune to subsequent Cryptosporidium infection is unclear.