Hundreds of babies suffering from rotavirus, the most common cause of diarrhea, have been brought to the emergency room at Kaplan Medical Center in Rehovot since the beginning of November, and many others are hospitalized elsewhere. Rotavirus infections are most common between November and February, and most patients are between one month and 18 months old. Kaplan Medical Center nurses said the hospital was isolating all cases. The virus is particularly a problem in child-care centers and pediatric wards, and almost all children have had a rotavirus infection by age five. A severe infection, rotavirus gastroenteritis, is the leading cause of severe, dehydrating diarrhea in infants and young children. A vaccine that protects against rotavirus is not part of the basket of immunizations provided at tipat halav (family health) centers due to insufficient resources. Asked to comment on the Kaplan cases, a Health Ministry spokeswoman said that cases of rotavirus were not on the list of diseases that must be reported by doctors to the district health offices. Thus, the ministry "has no data" on the number of children infected or the number who have been hospitalized. A rotavirus vaccine is registered in Israel, and can be purchased with a doctor"s prescription, the spokeswoman said, but it was not yet included in the basket of immunizations. She did not know whether the ministry had carried out a cost-benefit study to determine whether vaccinating all infants against rotavirus at state expense would save money wasted on hospitalization and treatment. In the US alone, rotavirus infections are responsible for some 3,000,000 cases of diarrhea and 55,000 hospitalizations for diarrhea and dehydration in children under five annually. Although these infections cause relatively few deaths in the US, the diarrhea caused by rotavirus results in more than 500,000 annual deaths worldwide. The incubation period for rotavirus disease is approximately two days, with symptoms that include vomiting and watery diarrhea for three to eight days, and often fever and abdominal pain. Immunity after infection is incomplete, but repeat infections tend to be less severe than the original one. The diarrhea may be severe enough to cause dehydration, whose signs are thirst, irritability, restlessness, lethargy, sunken eyes, a dry mouth and tongue, dry skin and less-than-normal urination. The virus passes in the stool of infected persons before and after they have symptoms of the illness. Children can become infected if they put their fingers in their mouths after touching something that has been contaminated by the stool of an infected person. Caregivers in day-care centers can spread the virus, especially if they do not wash their hands after changing diapers. The American Academy of Pediatrics recommends that rotavirus vaccine be given to all infants in three oral doses at two, four and six months of age. It prevents three-quarters of all cases and 98 percent of severe cases.