Issue: November 2012
October 18, 2012
2 min read

Norovirus in nursing homes increased mortality, hospitalizations

Issue: November 2012
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SAN DIEGO — Norovirus outbreaks in nursing homes were associated with increased mortality and hospitalizations, according to study findings presented here at ID Week 2012 and published simultaneously in The Journal of the American Medical Association.

“Outbreaks of acute gastroenteritis are common in nursing homes,” Tarak Trivedi, BS, a CDC applied epidemiology fellow and a medical student at the University of Chicago Pritzker School of Medicine, said during his presentation. “Annually, more than 1,000 outbreaks of acute gastroenteritis are reported by nursing homes across the country. This is probably a fraction of the true burden of the disease because of underreporting. Only about 50% of the outbreaks are laboratory-confirmed, and 86% of the laboratory-confirmed outbreaks are due to norovirus.”

Trivedi and colleagues conducted a retrospective cohort study that included 308 nursing homes in Oregon, Pennsylvania and Wisconsin. The nursing homes had reported 407 norovirus outbreaks from 2009 to 2010. Deaths and hospitalizations were identified using the Medicare Minimum Data Set.

During this time frame, there were 67,730 hospitalizations and 26,055 deaths among the nursing home residents in these 308 homes. During outbreaks, the hospitalization rate was 124 hospitalizations per home-year, and during non-outbreak times, the hospitalization rate was 109.5 hospitalizations per home-year. After adjustment for seasonality, the rate ratio was 1.09 (95% CI, 1.05-1.14).

During outbreaks, the mortality rate was 53.7 deaths per home-year, and during non-outbreak times, the mortality rate was 41.9 deaths per home-year. The rate ratio was 1.11 (95% CI, 1.04-1.18). Trivedi said the elevated hospitalization rates were concentrated during the first 2 weeks of the outbreak, and elevated mortality rates were concentrated during the first week.

The researchers also evaluated the effect of registered nursing hours on hospitalizations and mortality. Mortality increases were only found in homes that had less than 0.75 registered nursing hours per bed. There was no effect on hospitalizations.

“The finding that norovirus outbreaks are associated with an 11% increase in mortality challenges the notion that norovirus only causes a benign illness,” Trivedi said. “Norovirus is highly infectious and the high number of hospitalizations during outbreaks presents a risk of nursing home to hospital transmission. The association of increased mortality in homes with less than 0.75 registered nursing hours per patient is consistent with findings of other studies and also supports the recommendation of a 2001 report to Congress on the recommended 0.75 registered nursing hours per patient.”

For more information:

Trivedi T. #89. Presented at: ID Week 2012; Oct. 16-19, 2012; San Diego.

Trivedi T. JAMA. 2012;doi:10.1001/jama.2012.14023.