Norovirus infection has become the leading cause of acute gastroenteritis in children under 5 in the U.S.
Payne et al. report in The New England Journal of Medicine that norovirus infection leads to an estimated 14,000 hospitalizations, 281,000 emergency room visits, and 627,000 outpatient visits a year.
The virus causes severe stomach pain, nausea, diarrhea and vomiting. According to the Centers for Disease Control and Prevention, it leads to 800 
deaths a year, but the vast majority of people infected recover completely.
For the new study, the researchers counted laboratory-confirmed cases in three United States counties in 2009 and 2010, so the sample may not be representative of the entire country. During that period, norovirus was confirmed in about 20 percent of cases of acute gastroenteritis in children. Infection with another virus, rotavirus, has become less common since the introduction of a rotavirus vaccine.
There is no vaccine and no cure for norovirus infection, and it is highly contagious. There are various strains of the virus, and some may be more potent than others.
Background
Cases of rotavirus-associated acute gastroenteritis have declined since the introduction of rotavirus vaccines, but the burden of norovirus-associated acute gastroenteritis in children remains to be assessed.
Methods
We conducted active surveillance for laboratory-confirmed cases of norovirus among children younger than 5 years of age with acute gastroenteritis in hospitals, emergency departments, and outpatient clinical settings. The children resided in one of three U.S. counties during the years 2009 and 2010. Fecal specimens were tested for norovirus and rotavirus. We calculated population-based rates of norovirus-associated acute gastroenteritis and reviewed billing records to determine medical costs; these data were extrapolated to the U.S. population of children younger than 5 years of age.
Results
Norovirus was detected in 21% of young children (278 of 1295) seeking medical attention for acute gastroenteritis in 2009 and 2010, with norovirus detected in 22% (165 of 742) in 2009 and 20% (113 of 553) in 2010 (P=0.43). The virus was also detected in 4% of healthy controls (19 of 493) in 2009. Rotavirus was identified in 12% of children with acute gastroenteritis (152 of 1295) in 2009 and 2010. The respective rates of hospitalization, emergency department visits, and outpatient visits for the norovirus were 8.6, 146.7, and 367.7 per 10,000 children younger than 5 years of age in 2009 and 5.8, 134.3, and 260.1 per 10,000 in 2010, with an estimated cost per episode of $3,918, $435, and $151, respectively, in 2009. Nationally, we estimate that the average numbers of annual hospitalizations, emergency department visits, and outpatient visits due to norovirus infection in 2009 and 2010 among U.S. children in this age group exceeded 14,000, 281,000, and 627,000, respectively, with more than $273 million in treatment costs each year.
Conclusions
Since the introduction of rotavirus vaccines, norovirus has become the leading cause of medically attended acute gastroenteritis in U.S. children and is associated with nearly 1 million health care visits annually. (Funded by the Centers for Disease Control and Prevention.)