Norovirus overtakes rotavirus as leading GI illness in US kids

Mar 21, 2013 (CIDRAP News) – Norovirus has eclipsed rotavirus as the leading cause of gastroenteritis in US children and carries substantial infection and treatment costs, according to a new study led by a research team at the Centers for Disease Control and Prevention (CDC).

The study is the first to gauge the burden of lab-confirmed illness from norovirus in kids and comes at a time when gastroenteritis illness rates from rotavirus are falling due to the use of a vaccine and as health officials are gathering norovirus information in advance of a vaccine that's on the development horizon.

The CDC estimates that norovirus infection, an extremely contagious disease spread mostly through contact with sick people and contaminated food, water, and surfaces, leads to more than 21 million infections and 800 deaths in the United States each year.

To assess norovirus patterns, researchers conducted surveillance for lab-confirmed cases in three counties centered in Rochester, N.Y., Nashville, and Cincinnati. CDC researchers and their partners from the three counties published their findings today in the New England Journal of Medicine.

They looked at children under age 5 years who needed medical care for gastroenteritis from October 2008 through September 2010. The study included about 141,000 children. The team calculated population-based rates of norovirus gastroenteritis, reviewed billing records to determine medical costs, and extrapolated the findings to all US kids younger than 5.

Norovirus was detected at comparable levels over the 2 years: 21% during the first and 20% in the second. In a control group of healthy kids the first year, 4% had norovirus infection. Rotavirus was detected in 12% of kids seeking care for gastroenteritis for both years.

Overall, the investigators found that norovirus infections lead to nearly 1 million medical visits in young kids each year. More specifically, rates of hospitalization, emergency department visits, and outpatient visits for norovirus in 2009 were 8.6, 146.7, and 367.7 per 10,000 children under age 5 in 2009. For 2010 the rates were lower at 5.8, 134.3, and 260.1 per 10,000 children, respectively.

About half of the medical visits for norovirus were in children ages 6 to 18 months old, and infants and 1-year-olds were more likely to be hospitalized than were older children.

In terms of cost, researchers estimated that over the first year the hospitalization cost per illness was $3,918, an emergency department visit was $435, and an outpatient visit was $151.

Extrapolating the numbers to the wider US population of kids under age 5, the investigators estimated that visits to hospitals, emergency departments, and outpatient clinics exceeded 14,000, 281,000, and 627,000, respectively.

They put the total bill for annual treatment costs for norovirus illness in the age-group at more than $273 million each year.

First author Daniel Payne, PhD, MSPH, an epidemiologist with the CDC's Division of Viral Diseases, said in a CDC press release that the study confirms that medical visits for rotavirus infections have decreased. "Also, our study reinforces the success of the US rotavirus vaccination program and also emphasizes the value of specific interventions to protect against norovirus illness." Payne referred specifically to norovirus vaccines in development.

During the study period the group found a shift in the GII.4 norovirus variant, from G11.4 Minerva the first year to GII.4 New Orleans the second year. The authors noted that those findings, plus the recent identification of a novel GII.4 Sydney 2012 variant, may help experts pinpoint the best vaccine candidates and target populations for vaccination.

Payne DC, Vinje J, Szilagyi PG, et al. Norovirus and medically attended gastroenteritis in US children. N Engl J Med 2013 Mar 21;368(12):1121-30 [Abstract]

See also:

Mar 21 CDC press release

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