Rotavirus is a genus of double-stranded RNA viruses in the family Reoviridae. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Immunity develops with each infection, so subsequent infections are less severe; adults are rarely affected. There are ten species of the genus, referred to as A, B, C, D, E, F, G, H, I and J. Rotavirus A, the most common species, causes more than 90% of rotavirus infections in humans.