SAN DIEGO — Norovirus outbreaks in nursing homes are associated with increased rates of all-cause death and hospital admission for residents, researchers reported.
In a retrospective 2-year analysis of nursing homes in three states, hospital admissions rose 9% during outbreaks and mortality rates rose 11%, according to Tarak Trivedi, BS, a medical student at the University of Chicago Pritzker School of Medicine in Chicago, and colleagues.
The findings suggest — but do not prove — that norovirus is responsible for the increased risk to nursing home residents, Trivedi and colleagues reported at the IDWeek meeting here and online in the Journal of the American Medical Association.
“As a next step,” the investigators concluded, “research should be directed to determine if this increase is directly attributable to norovirus infection.”
One other possibility, they noted, is that a norovirus outbreak may lead to alterations in the pattern of care for uninfected residents, which, in turn, leads to more deaths and hospital admissions.
While it has long been suspected that norovirus is responsible for much morbidity and mortality in nursing homes, it has been difficult to tease out the effect, because hospital admissions and deaths are common among the vulnerable, elderly residents, Trivedi and colleagues noted.
To help clarify the issue, they used Medicare records and the CDC’s National Outbreak Reporting System to examine all reported outbreaks in nursing homes in three states, Oregon, Wisconsin, and Pennsylvania. The three states were selected because they had the greatest number of reported outbreaks, which would minimize underreporting.
Over the study period — from January 2009 through December 2010 — 308 nursing homes in the three states reported 407 norovirus outbreaks. Of a total of 616 nursing home-years of follow-up, 20 took place during the outbreaks, the researchers reported.
Overall, 67,730 hospital admissions and 26,055 deaths took place during the study, Trivedi and colleagues reported. The median duration of outbreaks was 13 days, and hospital admissions and deaths were reported in 29% and 7% of outbreaks, respectively.
During outbreaks, they found that hospital admission rates were 124.0 per nursing home per year, compared with 109.5 per nursing home-year during non-outbreak periods.
Those figures yielded a seasonally adjusted rate ratio of 1.09 (95% CI 1.05 to 1.14, P<0.001).
Similarly, mortality rates were 53.7 deaths per nursing home-year during outbreaks, versus 41.9 in non-outbreak periods, the researchers reported.
The seasonally adjusted rate ratio was 1.11 (95% CI 1.05 to 1.18).
Increases in admissions were concentrated in the first 2 weeks of outbreaks, while deaths were mostly in the initial week, Trivedi and colleagues found.
Homes with less than 0.75 hours a day per resident of registered nursing care had increased mortality rates during outbreaks compared with non-outbreak periods. The rate ratio was 1.26 (95% CI 1.14 to 1.40).
There was no increased risk in homes with a greater number of daily RN hours per resident, the researchers reported.
There was no similar pattern for hospital admission rates.
The researchers cautioned, among other things, that the effect might arise from the disruption caused by the outbreak rather than the virus itself. High attack rates may mean that affected residents need more care, while ill staff members are encouraged to stay home.
The findings “speak toward public health measures to try to prevent outbreaks,” commented Carol Chenoweth, MD, of the University of Michigan Health System in Ann Arbor, Mich., who moderated the session at which the story was presented.
Clinicians are aware that the virus has a variable presentation and in some patients can cause severe disease, she told MedPage Today. But even they may not be aware of the extent of the issue. “I was astounded” by the large number of outbreaks over a 2-year period, she said.
One implication of the study, Chenoweth said, may be a need for “more oversight of infection control in nursing homes.”
Source: Med Page Today at http://www.medpagetoday.com/InfectiousDisease/GeneralInfectiousDisease/35409?utm_content=&utm_medium=email&utm_campaign=DailyHeadlines&utm_source=WC&xid=NL_DHE_2012-10-19&eun=g514381d0r&userid=514381&[email protected]&mu_id