Factors associated with the transmission of pandemic (H1N1) 2009 among hospital healthcare workers in Beijing, China

BACKGROUND With the increase in patient activity during the 2009 H1N1 pandemic, came an associated increase in occupational infections of healthcare workers (HCWs). OBJECTIVES The aim of this study was to examine factors associated with the transmission of pandemic (H1N1) 2009 among HCWs. METHODS A 1:4 matched case-control study by hospital, ward, age, and gender was conducted in HCWs from hospitals in Beijing during February 2010. Cases were diagnosed with pandemic (H1N1) 2009, and controls had neither influenza-like illness nor diagnosis with pandemic (H1N1) 2009 during August 2009 to January 2010. Information during 7 days before symptom onset of case was collected, and controls were queried about the same period. RESULTS A total of 51 cases identified via National Notifiable Infectious Disease Surveillance System participated in this study. Controls were matched to cases for a total of 255 individuals. About 19·6% (10/51) of cases and 26·0% (53/204) of controls recalled they had conducted a high-risk procedure on a patient with pandemic (H1N1) 2009. 72·5% (37/51) of cases and 71·6% (146/204) of controls stated they wore medical masks in ≥80% of working time. Only 5·9% (3/51) and 36·3% (74/204) of cases and controls, respectively, reported receiving pandemic vaccination. Participants receiving pandemic vaccination had a significantly lower risk of infection during the pandemic (OR = 0·150, 95% CI: 0·047-0·479, P = 0·001). The estimated vaccine effectiveness was 85·0%. CONCLUSIONS We showed a high vaccine effectiveness of the pandemic vaccine and that vaccination was the only factor significantly associated with risk of infection in HCWs.