 Cholera is a severe diarrhea illness caused by bacteria. The purpose of this study is to better understand how the immune systems of people in Dhaka, Bangladesh, fight infection with cholera. Understanding immune responses that influence the outcome of infection with cholera can assist in the development of more effective cholera vaccines. The International Center for Diarrheal Diseases Research, Bangladesh ICDDR,B will enroll in this study 75 patients with acute cholera and 250 of their household contacts. Individuals ages 2-60 years are eligible. Study participation will last 1 year for cholera patients and 30 days for household contacts. Participants will come to the ICDDR,B for 3 household contacts or 4 cholera patients study visits, and field workers will visit them at home at other times. For all participants, blood samples will be taken at each of the ICDDR,B visits. Household contacts will have rectal swabs taken at 2 ICDDR visits and during field worker visits. 