Cryptosporidiosis is recognized as a major cause of diarrhea worldwide. In addition to infection of the gastrointestinal tract and associated fecal-oral transmission, there is evidence that Cryptosporidium can infect the respiratory tract. Of particular interest are numerous reports indicating that respiratory symptoms occur with considerable frequency in subjects with intestinal cryptosporidiosis although the etiology of the respiratory symptoms was never investigated. The association between respiratory symptoms and intestinal cryptosporidiosis is particularly strong in children with questionable nutritional status. This study will evaluate the prevalence and clinical presentation of respiratory cryptosporidiosis among children with diarrhea in Mulago Hospital, Kampala, Uganda. The study will screen approximately 1536 children aged 9-36 months who present to the Acute Care Unit of Mulago Hospital in Kampala, Uganda, with acute or persistent diarrhea. Based on the results of fecal testing, 480 children will be actively selected to undergo further sample collection in 2 groups. Group 1 will be comprised of children with Cryptosporidium-positive stools, approximately 50% of whom are expected to have cough (n=384). Group 2 will be comprised of children with Cryptosporidium-negative stools and cough (n=96). The primary objectives of the study are: to establish the prevalence of cough in children with diarrhea due to Cryptosporidium infection; to establish the prevalence of respiratory tract cryptosporidiosis in children with diarrhea due to Cryptosporidium infection; to establish the prevalence of respiratory tract cryptosporidiosis in children with diarrhea due to other causes; and to determine whether respiratory Cryptosporidium infection in children is associated with increased respiratory rates and decreased oxygen saturation levels. To address these objectives, the study will focus on whether Cryptosporidium oocysts can be recovered from induced sputum of subjects who have acute or persistent diarrhea and are concurrently experiencing a cough or unexplained tachypnea or hypoxemia. The primary clinical measures include: duration of diarrhea (days); presence and duration of cough (days); respiratory rate at presentation and if dehydrated, after rehydration; oxygen saturation (as measured by pulse oximetry) at presentation; and oxygen therapy requirement and oxygen saturation after 30 minutes of oxygen therapy if initial saturation is <92%. Primary parasitological measures include: presence or absence of Cryptosporidium in stool (as detected by modified acid fast staining and PCR); presence or absence of Cryptosporidium in sputum (as detected by PCR); and presence or absence of Cryptosporidium in saliva (as detected by PCR). Secondary clinical measures include: HIV status (determined by voluntary HIV testing via enzyme-linked immunosorbent assay + reverse transcriptase PCR in children aged less than 18 months); CD4+ counts/percentages (as measured by flow cytometry in children tested for HIV); concurrent respiratory infection (as determined by processing of sputum for routine bacterial pathogens, tuberculosis and pneumocystis jirovecii pneumonia; anemia (determined by hemoglobin measurement from complete blood count); and nutritional status (as determined from the weight-for-age score, height-for-age score, weight-for-height score, head circumference, and mid upper arm circumference). Secondary parasitological measurements include: species of Cryptosporidium in stool, in sputum, and in saliva (as determined by restriction fragment length polymorphism). Subject participation duration in the study is dependent on the health status of the child at admission and the extent of clinical care required. In uncomplicated cases, subject duration may be as short as 4 hours. In subjects requiring extensive clinical care subject duration may extend to 2 days.