The treatment of gastroenteritis in children focuses on preventing dehydration. A child with minimal or no dehydration should be encouraged to continue his or her usual diet plus drink adequate fluids. Many studies have shown that a child's regular diet reduces the duration of diarrhea. Oral rehydration therapy with a rehydration solution can be used to treat diarrhea in children with mild to moderate dehydration. Ondansetron can decrease vomiting or help avoid the need for intravenous fluid, but it increases episodes of diarrhea. Probiotics can be used to shorten the course of diarrhea. Good handwashing reduces the incidence of acute gastroenteritis, but not rotavirus. The introduction of two rotavirus vaccines in the United States in 2006 significantly reduced the incidence of rotavirus gastroenteritis. The oral, live vaccines have strong safety records, despite a minimal incidence of intussusception.