Rotavirus is a virus that causes severe diarrhea . It can also cause vomiting, fever and dehydration. It is the leading cause of diarrhea in infants and young children. Almost all children in the U.S. are likely to be infected with rotavirus before their 5th birthday. Infections happen most often in the winter and spring. It is very easy for children with the virus to spread it to other children and sometimes to adults. Once a child gets the virus, it takes about two days to become sick. Vomiting and diarrhea may last from three to eight days. Treatment is replacing lost body fluids. Having your child drink products with water, sugar and minerals usually helps. Some children need to go to the hospital for IV fluids. A vaccine can protect your child against the virus.