Cryptosporidiosis is a relatively common parasitic infection that sometimes causes symptoms of watery diarrhea and abdominal cramps. Diagnosed infections typically last 12 weeks in immunocompetent persons, but may be unusually protracted. Infections can be difficult to control among the immunocompromised, notably AIDS patients. Repeated studies suggest that the prevalence of cryptosporidiosis among young children, particular those in large child-care facilities, is surprisingly high. Many of these infections are asymptomatic.
Given the number of asymptomatic and undiagnosed infections, surveillance data can be difficult to interpret, although they have been used to identify a number of outbreaks over the years, most commonly associated with childcare or water (both drinking and recreational). Theoretical concerns about the possibility of crypto transmission in unfiltered drinking water are leading a number of communities, including Portland, to consider expensive changes to routine water treatment methods.