Cryptosporidium is an intestinal parasite that causes diarrhea in children and adults. In addition to infection of the stomach, this parasite can infect the respiratory system causing a cough and/or problems breathing. This study will enroll 480 children between the ages of 9 and 36 months who come to Mulago Hospital for treatment of diarrhea. Researchers believe a large number of children with diarrhea and cough will have the parasite present in their sputum (mucus coughed up). Researchers also believe that children who have respiratory tract cryptosporidiosis may have a cough, increased number of breaths per minute, and/or a lower oxygen level. Blood, stool, saliva, and sputum samples will be collected from all children in the study and tested for Cryptosporidium. Children too young to provide a sputum sample will have a tube placed to collect a mucus sample from the lungs. Study participation may be as short as 4 hours or as long as 2 days depending on each child's health.