Surveillance for will be conducted at the Matlab Diarrhoeal Hospital and the two community treatment centres at Nayergaon and Kalirbazaar, which facilitate quick and easy accessibility of treatment for life-threatening diarrhoeal diseases from the HDSS area. The main study outcome will be episodes of rotavirus diarrhoea among children admitted to Matlab Diarrhoeal Hospital or either of the two community treatment centres (Nayergaon and Kalirbazaar). Study personnel will record the child's symptoms and clinical history, and collect a fecal specimen for laboratory testing for rotavirus. The identity of the child will be confirmed through the HDSS subject identification number system. All patients coming to the Matlab Diarrhoea Hospital and Nayergoan community treatment centre from these villages are already included in the Matlab diarrhoea surveillance system, and faecal samples are routinely tested for rotavirus and other pathogens, with results linked to demographic and health databases of the HDSS. Kalirbazaar treatment centre is not currently included in the current surveillance system, but we will establish surveillance at this centre during this study. For enrolled participants who present to one of the treatment facilities, illness information and test results will be linked to HDSS demographic data and study-specific data collected at enrolment through the subject's HDSS number. For residents not enrolled who present to a treatment facility, illness information will be linked only to HDSS demographic data, as is already being done as part of surveillance activities.