Infections of the small intestine, including the duodenum, jejunum, and ileum, generally result from the ingestion of contaminated food or water. The majority of infections are caused by Escherichia coli, rotavirus, Giardia lamblia, and Cryptosporidium parvum. Annual incidence for infections of the small intestine varies according to the pathogen. Cryptosporidiosis occurs worldwide, but is more prevalent in underdeveloped countries with infection rates as high as 32%. Infection with Giardia spp. is often asymptomatic; a broad spectrum of clinical symptoms can occur including diarrhea, malaise, abdominal distension, weight loss, abdominal cramps, and flatulence. E. coli (ETEC) utilize fimbrial colonization factor antigens to adhere to the small bowel mucosa. ETEC subsequently produce enterotoxins which increase secretion of fluid and electrolytes from the mucosa of the small bowel. Cryptosporidiosis is manifested as profuse watery diarrhea, although the infection can be asymptomatic.