 Cryptosporidium parvum C. parvum is a parasite that can cause chronic diarrhea and is a significant problem for HIV infected children in developing countries. C. parvum infection can be treated with the drug nitazoxanide NTZ. However, NTZ has not been tested in HIV infected children. The purpose of this study is to test the safety of NTZ in HIV infected children who have chronic diarrhea caused by C. parvum. 