title: Institutional risk factors for norovirus outbreaks in Hong Kong elderly homes: a retrospective cohort study.
abstract: BACKGROUND
  Most of the institutional outbreaks of norovirus in Hong Kong occur in elderly homes, the proportion being 69% in 2006. Residents in elderly homes are a special population seriously affected by norovirus infections, it is necessary to investigate the risk factors of the norovirus outbreaks in Hong Kong elderly homes at the facility level.
  
  
  METHODS
  A cohort of 748 elderly homes was followed up from January 2005 to December 2007; each elderly home was treated as one observation unit and the outcome event was the norovirus outbreak. Cox regression models were fitted to estimate the rate ratio (RR) and 95% confidence interval (CI) for the potential risk factors.
  
  
  RESULTS
  A total of 276 norovirus outbreaks were confirmed during the study period; the outbreak rate was 12.2 (95% CI: 9.9-14.6) per 100 home-years; elderly homes with a larger capacity (RR = 1.4, 95% CI: 1.3-1.5 (per 30-resident increment)), a higher staff-to-resident ratio (RR = 1.2, 95% CI: 1.1-1.3 (per 1/30 increment) and better wheelchair accessibility (RR = 2.0, 95% CI: 1.3-3.2) were found to have an elevated norovirus outbreak rate in Hong Kong elderly homes; Elderly homes with partitions between beds had a lower rate of norovirus outbreaks (RR = 0.6, 95% CI: 0.4-0.8).
  
  
  CONCLUSIONS
  Elderly home capacity, staff-to-resident ratio and wheelchair accessibility were risk factors for norovirus outbreaks in Hong Kong elderly homes. Partitions between beds were a protective factor of norovirus outbreaks. These results should be considered in the infection control in Hong Kong elderly homes.
authors.affiliation: School of Public Health and Primary Care, Chinese University of Hong Kong, Hong Kong SAR, China.
authors.forename: Hualiang
authors.initials: H
authors.lastname: Lin
authors.forename: Sammy
authors.initials: S
authors.lastname: Ng
authors.forename: Shelley
authors.initials: S
authors.lastname: Chan
authors.forename: Wai Man
authors.initials: WM
authors.lastname: Chan
authors.forename: Krystal C K
authors.initials: KC
authors.lastname: Lee
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Ho
authors.forename: Linwei
authors.initials: L
authors.lastname: Tian
mesh_terms: D000368:Aged; D017250:Caliciviridae Infections / Q000453:epidemiology* / Q000209:etiology; D015331:Cohort Studies; D004196:Disease Outbreaks; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D008297:Male; D029322:Norovirus / Q000302:isolation & purification*; D012112:Residential Facilities; D012189:Retrospective Studies; D012307:Risk Factors