Risk factors for influenza A(H1N1)pdm09 seroconversion among general population in southern China

Abstract

Introduction: China experienced and shouldered a great burden of the 2009 influenza pandemic. However, little is known about the risk factors for influenza A(H1N1)pdm09 infection in general population of mainland China. Objective: To assess risk factors associated with influenza A(H1N1)pdm09 seroconversion among general population in Southern China. Method: A household-based cohort study was conducted in Guangzhou, applied multistage random sampling across space and social gradient. Socio-demographic data and serum specimens of eligible participants were collected by face-to-face interview after December 2009. Haemagglutination inhibition assay was performed to measure the titre against A(H1N1)pdm09. Seroconversion was defined as a four-fold or greater increase in titre level between the paired serum specimens. A generalised estimating equation model was applied to identify risk factors, considering the household clustering. Results: Between December 2009 and May 2012, paired sera of 1016 participants from 608 households were collected and tested. The overall seroconversion rate of the almost unvaccinated cohort was 13.1% (95% CI, 11.0-15.2). Participants under 50 years old were at higher risk of seroconversion than participants aged 60 or over. The odds ratio (OR) for participants of aged 40-49, aged 30-39, aged 20-29 and aged 2-19 were 2.10 (95%CI, 1.07-3.25), 2.93 (95%CI, 1.36-6.28), 3.09 (95%CI, 1.47-6.52) and 2.65 (95% CI, 1.17-6.01), respectively. Residents from Luogang district were less likely to seroconvert (OR=0.41; 95% CI 0.22-0.77). Highest monthly household income group (>6,000 RMB) resulted in a lower risk of seroconversion too (OR=0.25; 95%CI, 0.08-0.78). Conclusion: Even in the post-epidemic period, a higher proportion of general population of mainland China remained susceptible to influenza A(H1N1)pdm09 virus. Younger people had higher risk of seroconversion than the elderly, whereas, people from higher monthly household income group and being a resident of Luogang district were at lower risk of seroconversion. These findings suggested a significant implication in the preparedness of future pandemic.