Norovirus is the leading cause of infection outbreaks in US hospitals

Norovirus, a pathogen that often causes food poisoning and gastroenteritis, was responsible for 18.2 percent of all infection outbreaks and 65 percent of ward closures in U.S. hospitals during a two-year period, according to a new study published in the February issue of the American Journal of Infection Control (AJIC), the official publication of APIC - the Association for Professionals in Infection Control and Epidemiology.

A team of researchers from Chartis, Main Line Health System, Lexington Insurance Company, and APIC Consulting Services collected survey responses from 822 APIC members who work in U.S. hospitals regarding outbreak investigations at their institutions during 2008 and 2009. The study was conducted to determine how often outbreak investigations are initiated in U.S. hospitals, as well as the triggers for investigations, types of organisms, and control measures including unit closures.

Thirty-five percent of the 822 hospitals responding had investigated at least one outbreak in the previous two years. Four organisms caused nearly 60 percent of the outbreaks: norovirus (18.2 percent), Staphylococcus aureus (17.5 percent), Acinetobacter spp (13.7 percent), and Clostridium difficile (10.3 percent). These results reflect 386 outbreak investigations reported by 289 hospitals over a 24-month period.

Medical/surgical units were the most common location of outbreak investigations (25.7 percent), followed by surgical units (13.9 percent). Nearly one-third (29.2 percent) of outbreaks were reported in a category that included emergency departments, rehabilitation units, long-term acute care hospitals, psychiatric/behavioral health units, and skilled nursing facilities. According to the results, the average number of confirmed cases per outbreak was 10.1 and the average duration was 58.4 days. Unit closures were reported in 22.6 percent of the cases, causing an average 16.7 bed closures for 8.3 days.

Of reported outbreaks, only 132 (52.2 percent) of investigations were reported to an external agency, with just 71 (28.4 percent) involving assistance in the investigation by an external resource. In most states, reporting to the state health department is required and can provide hospitals with expertise to expedite and expand their outbreak investigations.

"It is clear that outbreaks of healthcare-associated infections occur with some frequency in hospitals as well as nonacute settings," state the authors. "An infection prevention and control program and its staff should be prepared for all aspects of an outbreak investigation through written policies and procedures as well as communication with internal and external partners."