Rotavirus is the most common cause of severe diarrhea among infants and young children, accounting for close to 50% of hospitalizations for that. It is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. Rotavirus A, the most common of the 5 known species, causes more than 90% of infections in humans. Worldwide nearly 500,000 children under five years of age still die from rotavirus infection each year and almost two million more become severely ill. In addition to its impact on human health, rotavirus also infects animals and is a pathogen of livestock.

Rotavirus is usually an easily managed disease of childhood. Rotavirus is transmitted by the fecal-oral route, via contact with contaminated hands, surfaces and objects, and possibly by the respiratory route. The feces of an infected person can contain more than 10 trillion infectious particles per gram; fewer than 100 of these are required to transmit infection to another person. It infects and damages the cells that line the small intestine and causes gastroenteritis.

Rotavirus gastroenteritis is a mild to severe disease characterized by vomiting, watery diarrhea, and low-grade fever. Once a child is infected by the virus, there is an incubation period of about two days before symptoms appear. Symptoms often start with vomiting followed by four to eight days of profuse diarrhea. Dehydration is more common in rotavirus infection than in most viruses caused by bacterial pathogens, and is the most common cause of death related to rotavirus infection.