The oocysts contains up to 4 sporozoites that are bow-shaped.As few as 2 to 10 oocysts can initiate an infection. The parasite is located in the brush border of the epithelial cells of the small intestine. They are mainly located in the jejunum. When the sporozoites attach the epithelial cells membrane envelops them. Thus, they are "intracellular but extracytoplasmic". The parasite can cause damage to the microvilli where it attaches. The infected human excretes the most oocysts during the first week. Oocysts can be excreted for weeks after the diarrhea subsides from infections by C. parvum or C. hominis; however, immunocompetent individuals with C. muris infections have been observed excreting oocysts for seven months.The immune system reduces the formation of Type 1 merozoites as well as the number of thin-walled oocysts. This helps prevent autoinfection. B cells do not help with the initial response or the fight to eliminate the parasite. Previous infection in immunocompetent individuals produces little resistance to future infection, however it may decrease the severity of disease and the number of oocysts excreted. Diagnosis
There are many diagnostic tests for Cryptosporidium. They include microscopy, staining, and detection of antibodies. Microscopy can help identify oocysts in fecal matter. To increase the chance of finding the oocysts, the diagnostician should inspect at least 3 stool samples. There are several techniques to concentrate either the stool sample or the oocysts. The modified formalin-ethyl acetate (FEA) concentration method concentrates the stool.
As of 10 September 2007 the Utah Department of Health had reported 1302 cases Archived 25 September 2007 at the Wayback Machine of cryptosporidiosis in the year; a more usual number would be 30. On 25 September the pools were reopened to those not requiring diapers, but hyperchlorination requirements were not lifted. On 21 September 2007, a Cryptosporidium outbreak attacked the Western United States: 230 Idaho residents, with hundreds across the Rocky Mountain area; in the Boise and Meridian areas; Utah, 1,600 illnesses; Colorado and other Western states — Montana, decrease. On 25 June 2008, Cryptosporidium was found in England in water supplies in Northampton, Daventry, and some surrounding areas supplied from the Pitsford Reservoir, as reported on the BBC. People in the affected areas were warned not to drink tap water unless it had been boiled. Anglian Water confirmed that 108,000 households were affected, about 250,000 people. They advised that water might not be fit for human consumption for many weeks. The boil notice was lifted for all the affected customers on 4 July 2008. Throughout the summer of 2008; many public swimming areas, water parks, and public pools in the Dallas/Fort Worth Metroplex of Texas suffered an outbreak of cryptosporidiosis. Burgers Lake in Fort Worth was the first to report such an outbreak. This prompted some, if not all, city-owned and private pools to close and hyperchlorinate. To the 13 August 2008 there were 400 reported cases of Cryptosporidium.