(UPI) -- More than 1,000 outbreaks of acute gastroenteritis are reported by U.S. nursing homes annually, but this is only a fraction of the cases, researchers say.
Tarak K. Trivedi, a fourth year medical student at the University of Chicago Pritzker School of Medicine, and colleagues conducted a study to assess the association between norovirus outbreaks and excess all-cause hospitalization and mortality in nursing homes.
Although nearly half of all reported nursing home gastroenteritis outbreaks are never confirmed because of challenges in performing diagnostic testing, norovirus is implicated in 86 percent of confirmed outbreaks, Trivedi said. Because hospitalizations and deaths are common among the vulnerable, elderly population in nursing homes, it is difficult to ascertain if there is actually a greater number of these events during norovirus outbreaks, Trivedi added.
The study involved 308 Medicare-certified nursing homes in Oregon, Wisconsin and Pennsylvania that reported at least one confirmed or suspected norovirus outbreak to the Centers for Disease Control and Prevention from January 2009 to December 2010. Deaths and hospitalizations occurring among residents of these nursing homes were identified through the Medicare Minimum Data Set.
The nursing homes in the study reported a total of 407 norovirus outbreaks. The median duration of outbreaks was 13 days -- 29 percent were hospitalized and 7 percent died.
The increase in hospitalizations was concentrated in the initial week and the subsequent week, and the increased mortality rate was concentrated in the initial week, relative to outbreak onset, but in subsequent weeks, the rates of hospitalizations and deaths returned to the levels observed in non-outbreak periods.
The study, published in the Journal of the American Medical Association, found nursing homes with lower daily registered nursing hours per resident had a significantly increased rate of mortality during norovirus outbreaks compared with baseline, while no increased risk was observed in homes with higher daily RN hours per resident.