Seroprevalence of Pandemic Influenza H1N1 in Ontario from January 2009–May 2010

BackgroundWe designed a seroprevalence study using multiple testing assays and population sources to estimate the community seroprevalence of pH1N1/09 and risk factors for infection before the outbreak was recognized and throughout the pandemic to the end of 2009/10 influenza season.
MethodsResidual serum specimens from five time points (between 01/2009 and 05/2010) and samples from two time points from a prospectively recruited cohort were included. The distribution of risk factors was explored in multivariate adjusted analyses using logistic regression among the cohort. Antibody levels were measured by hemagglutination inhibition (HAI) and microneutralization (MN) assays.
ResultsResidual sera from 3375 patients and 1024 prospectively recruited cohort participants were analyzed. Pre-pandemic seroprevalence ranged from 2%–12% across age groups. Overall seropositivity ranged from 10%–19% post-first wave and 32%–41% by the end of the 2009/10 influenza season. Seroprevalence and risk factors differed between MN and HAI assays, particularly in older age groups and between waves. Following the H1N1 vaccination program, higher GMT were noted among vaccinated individuals. Overall, 20–30% of the population was estimated to be infected.
ConclusionsCombining population sources of sera across five time points with prospectively collected epidemiological information yielded a complete description of the evolution of pH1N1 infection.

研究背景 本研究采用多种检测方法与多人群来源样本，旨在估算2009年大流行性甲型H1N1流感（pH1N1/09）的社区血清阳性率，并明确在疫情被发现之前、大流行期间直至2009/10流感季结束期间的感染危险因素。
研究方法 本研究纳入了2009年1月至2010年5月间5个时间点留存的血清标本，以及前瞻性招募队列中2个时间点采集的样本。在该队列中，采用logistic回归进行多变量校正分析，以探讨危险因素的分布特征。抗体水平通过血凝抑制试验（hemagglutination inhibition, HAI）和微量中和试验（microneutralization, MN）进行检测。
研究结果 本研究共分析了3375例患者的留存血清标本与1024名前瞻性招募队列参与者的样本。疫情前各年龄组的血清阳性率范围为2%~12%。第一波疫情后，总体血清阳性率为10%~19%，至2009/10流感季结束时，该比例升至32%~41%。不同检测方法间的血清阳性率及危险因素存在差异，尤其在老年组与不同疫情波次间差异更为显著。H1N1疫苗接种计划实施后，接种者的抗体几何平均滴度（GMT, geometric mean titer）更高。总体而言，估计有20%~30%的人群曾发生感染。
研究结论 结合5个时间点的多人群血清标本与前瞻性收集的流行病学信息，本研究完整阐明了2009年大流行性甲型H1N1流感（pH1N1/09）感染的流行演变过程。