89. Excess Hospitalizations and Mortality Associated with Norovirus Outbreaks in Nursing Homes Oregon, Pennsylvania, and Wisconsin, 2009-2010.
Session: Oral Abstract Session: Healthcare-Associated Outbreaks
Thursday, October 18, 2012: 9:15 AM
Room: Marriott Hall 3

Norovirus outbreaks are common in nursing homes in the US and affect vulnerable, elderly populations. Hospitalizations and deaths have been reported during norovirus outbreak investigations but a causal association remains unclear. We compared all-cause mortality and hospitalization rates in nursing homes during norovirus outbreak periods to rates during non-outbreak periods.


We constructed a retrospective cohort of Medicare-certified nursing homes in Oregon, Wisconsin, and Pennsylvania that reported at least one norovirus outbreak to the National Outbreak Reporting System (NORS) during January 2009 to December 2010. All deaths and hospitalizations occurring among residents of these nursing homes were identified through the Medicare Minimum Data Set (MDS). Using a random-effect Poisson regression model, we compared rates of all-cause hospitalization and mortality during outbreak time periods with rates during non-outbreak time periods, controlling for background seasonality in both outcomes.


The cohort consisted of 308 nursing homes that reported 407 norovirus outbreaks to NORS. Per MDS, there were 67,730 hospitalizations and 26,055 deaths in these homes during the 2-year study period. Hospitalization rates were 124.0 and 109.5 hospitalizations/home-year during outbreak and non-outbreak periods respectively, yielding a seasonally-adjusted rate ratio (aRR) of 1.09 (95% CI: 1.05–1.14, p<0.001). Similarly, mortality rates were 53.7 versus 41.9 deaths/home-year in outbreak versus non-outbreak periods; an aRR of 1.11 [95% CI: 1.04–1.18, p=0.001]. The increases in hospitalizations and mortality were concentrated in the first two weeks and the first week of the outbreak, respectively. The increase in mortality during outbreak periods was limited to nursing homes with < 0.75 daily registered nurse (RN) hours per bed. Residents over the age of 90 experienced the greatest increase in hospitalization and mortality rates during outbreaks.


Norovirus outbreaks were associated with a significant increase in all-cause hospitalization and mortality in nursing homes. Homes with older resident populations and lower RN hours-to-bed ratios may be the most at risk for increased mortality during norovirus outbreaks.

Tarak Trivedi, BS1, Traci DeSalvo, MPH2, Lore Lee, MPH3, Aimee Palumbo, MPH4, Maria E. Moll, MD5, Aaron T. Curns, MPH1, Aron J. Hall, DVM, MSPh1, Manish Patel, MD1, Umesh D. Parashar, MBBS, MPH1 and Ben A. Lopman, MSc, PhD1, (1)Centers for Disease Control and Prevention, Atlanta, GA, (2)Bureau of Communicable Diseases & Emergency Response, Wisconsin Division of Public Health, Madison, WI, (3)Oregon Public Health Division, Portland, OR, (4)Division of Infectious Disease Epidemiology, Pennsylvania Department of Health, Harrisburg , PA, (5)Pennsylvania Department of Health, Harrisburg, PA


T. Trivedi, Pfizer Inc.: The CDC Experience is a one-year fellowship in applied epidemiology at CDC made possible by a public/private partnership supported by a grant to the CDC Foundation from External Medical Affairs, Pfizer Inc. , Grant recipient

T. DeSalvo, None

L. Lee, None

A. Palumbo, None

M. E. Moll, None

A. T. Curns, None

A. J. Hall, None

M. Patel, None

U. D. Parashar, None

B. A. Lopman, None

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