Pandemic 2009 Influenza A (H1N1) Virus among Japanese Healthcare Workers: Seroprevalence and Risk Factors

OBJECTIVE. To evaluate the seroprevalence and risk factors for 2009 influenza A (H1N1) virus infection among healthcare personnel. DESIGN. Observational cross-sectional study. PATIENTS AND SETTING. Healthcare workers (HCWs) in an acute care hospital. METHODS. Between September 14 and October 4, 2009, before 2009 H1N1 vaccination, we collected serological samples from 461 healthy HCWs. Hemagglutination-inhibition antibody assays were conducted. To evaluate the risk factors of seropositivity for 2009 H1N1 virus, gender, age, profession, work department, usage of personal protective equipment, and seasonal influenza vaccination status data were gathered via questionnaires. RESULTS. Our survey showed that doctors and nurses were at highest risk of seropositivity for the 2009 H1N1 virus (odds ratio [OR], 5.25 [95% confidence interval {CI}, 1.21-22.7]). An increased risk of seropositivity was observed among pediatric, emergency room, and internal medicine staff (adjusted OR, 1.98 [95% CI, 1.07-3.65]). Risk was also higher among HCWs who had high titers of antibodies against the seasonal H1N1 virus (adjusted OR, 1.59 [95% CI, 1.02-2.48]). CONCLUSIONS. Seropositivity for the 2009 H1N1 virus was associated with occupational risk factors among HCWs. Infect Control Hosp Epidemiol 2012; 33(1):58-62