Cryptosporidiosis is transmitted via the fecal-oral route. This means that C. parvum is excreted in the feces of animals or humans and is ingested from contaminated food, soil, surfaces, or, most commonly, water. The infective stage of the parasite is the oocyst. To view the life cycle of C. parvum, click here. According to the CDC, the following are common ways to become infected with Cryptosporidium:

Accidentally putting something into your mouth or swallowing something that has come into contact with feces of a person or animal infected with Cryptosporidium.	8
Swallowing recreational water contaminated with Cryptosporidium (Recreational water includes water in swimming pools, hot tubs, jacuzzis, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with sewage or feces from humans or animals.) Note: Cryptosporidium can survive for days in swimming pools with adequate chlorine levels because its outer shell makes it resistant.	9
Eating uncooked food contaminated with Cryptosporidium. Thoroughly wash with clean, safe water all vegetables and fruits you plan to eat raw.	10
Accidentally swallowing Cryptosporidium picked up from surfaces (such as bathroom fixtures, changing tables, diaper pails, or toys) contaminated with feces from an infected person.4	11

It is also important to note that Cryptosporidiosis cannot be transmitted through contact with blood.