a1 Epidemic Intelligence Service assigned to the Oregon Public Health Division, Centers for Disease Control and Prevention, Atlanta, GA, USA
a2 Oregon Public Health Division, Portland, OR, USA
a3 Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA
To identify the epidemiological and genetic characteristics of norovirus (NoV) outbreaks and estimate the impact of NoV infections in an older population, we analysed epidemiological and laboratory data collected using standardized methods from long-term care facilities (LTCFs) during 2003–2006. Faecal specimens were tested for NoV by real-time reverse transcriptase–polymerase chain reaction. NoV strains were genotyped by sequencing. Of the 234 acute gastroenteritis (AGE) outbreaks reported, 163 (70%) were caused by NoV. The annual attack rate of outbreak-associated NoV infection in LTCF residents was 4%, with a case-hospitalization rate of 3·1% and a case-fatality rate of 0·5%. GII.4 strains accounted for 84% of NoV outbreaks. Median duration of illness was longer for GII.4 infections than non-GII.4 infections (33 vs. 24 h, P<0·001). Emerging GII.4 strains (Hunter/2004, Minerva/2006b, Terneuzen/2006a) gradually replaced the previously dominant strain (Farmington Hills/2002) during 2004–2006. NoV GII.4 strains are now associated with the majority of AGE outbreaks in LTCFs and prolonged illness in Oregon.
(Accepted March 17 2010)
(Online publication April 23 2010)
Part of the study findings were presented in the Tuesday Morning Seminar at the Centers for Disease Control and Prevention on 9 September, 2008 in Atlanta, GA, USA.