Until recently, rotavirus was the leading cause of gastrointestinal illness in young children in the United States. Before a vaccine was developed for the virus in 2006, “almost all children in the United States were infected with rotavirus before their 5th birthday,” according to the Centers for Disease Control and Prevention (CDC).  Now, a new study funded by CDC shows that norovirus, another virus that infects the intestine, has surpassed rotavirus as the leading cause of gastroenteritis among children under five treated at healthcare facilities.  Researchers analyzed the cases of 1,295 young children who received medical attention for gastrointestinal symptoms in 2009 and 2010 and found that 21 percent of them were confirmed to have a norovirus infection, while 12 percent were sickened by rotavirus. The study, published in the New England Journal of Medicine last week, estimates that norovirus accounts for 14,000 hospitalizations, 281,000 emergency department visits and 627,000 outpatient visits per year among children under five years old, for a total of almost 1 million health care visits annually. The approximate cost of a norovirus infection resulting in hospitalization is $3,918, according to the study, while the cost of an emergency room visit is around $435 and an outpatient visit is an estimated $151. Treating norovirus patients in this age group costs over $273 million per year, conclude the authors. Is this trend likely to continue in the future, or will a vaccine for norovirus reduce the incidence of this pathogen, as it did for rotavirus? “There are several norovirus vaccines that are in various stages of development. However, one norovirus vaccine is in phase III clinical trials,” said Dr. Daniel C. Payne, lead author of the study, in an email to Food Safety News, referring to a nasally administered vaccine that was proven effective in a study published in NEJM in December of 2011. “That vaccine is now being tested in a form for intramuscular injection among older adults,” said Payne. In the meantime, there are still precautions people can take to prevent the spread of norovirus, he noted. “Until specific interventions are available, the best ways to reduce the risk of norovirus infection are proper hand washing and good hygiene.” Norovirus is transmitted via the fecal-oral route, and is spread easily in confined spaces such as cruise ships, daycares and elderly homes. A norovirus infection is generally characterized by abdominal cramps, diarrhea and vomiting. More severe illness can occur in the elderly, small children and those with weakened immune systems. Payne says CDC is also analyzing the burden of norovirus illness among the elderly, “another population vulnerable to norovirus infection.”