Estimated incidence and number of outpatient visits for seasonal influenza in 2015-2016 in Beijing, China

Information on morbidity burden of seasonal influenza in China is limited. A multiplier model was used to estimate the incidence and number of outpatient visits for seasonal influenza by age group for the 2015-2016 season in Beijing, the capital of China, based on reported numbers of influenza-like illness consultations and proportions of positive cases from influenza surveillance systems in Beijing, general consultation rates and other parameters from previous studies, surveys and surveillance systems. An estimated total of 1 190 200 (95% confidence interval (CI) 830 400-1 549 900) cases of influenza virus infections occurred in Beijing, 2015-2016 season, with an attack rate of 55% (95% CI 39-72%). These infections resulted in an estimated 468 280 (95% CI 70 700-606 800) outpatient visits, with an attack rate of 22% (95% CI 03-28%). The attack rate of influenza virus infections was highest among children aged 0-4 years (319% (95% CI 219-419%)), followed by children aged 5-14 years (187% (95% CI 129-245%)). Our study demonstrated a substantial influenza-related morbidity in Beijing, China, especially among the preschool- and school-aged children. This suggests that development or modification of seasonal influenza targeted vaccination strategies need to recognize that incidence is highest in children.