An infection caused by the protozoan Cryptosporidium. Symptoms of cryptosporidiosis include diarrhea, nausea, vomiting, and lower abdominal cramping. In people with weakened immune systems, such as people with HIV, cryptosporidiosis can lead to severe and life-threatening loss of muscle and body mass and malnutrition. In people with HIV, chronic cryptosporidiosis (lasting more than 1 month) is an AIDS-defining condition.