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Open Access Research article

Institutional risk factors for norovirus outbreaks in Hong Kong elderly homes: a retrospective cohort study

Hualiang Lin1, Sammy Ng2, Shelley Chan2, Wai Man Chan2, Krystal CK Lee1, Suzanne C Ho1 and Linwei Tian1*

Author Affiliations

1 School of Public Health and Primary Care, Chinese University of Hong Kong, Hong Kong SAR, China

2 Department of Health, Hong Kong SAR, China

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BMC Public Health 2011, 11:297  doi:10.1186/1471-2458-11-297

Published: 11 May 2011

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.