Estimated infection rates and incidence rates of seasonal influenza in Beijing during the 2017-2018 influenza season

Objective The aim of the study was to estimate the infection rates and the incidence rates of seasonal influenza in Beijing in 2017-2018 influenza season. Methods A multiplier model was used to estimate the infection rates and incidence rates of seasonal influenza, taking the number of influenza-like illness (ILI) cases and the positive rates of influenza virus nucleic acid from the reports of ILI surveillance system and pathogenic surveillance system of influenza as the basis, along with the proportions of symptomatic infection, consultation rates by age groups and other relevant parameters. Results The estimated infection rate of influenza in Beijing during 2017-2018 influenza season was 10.46% (95%CI: 7.93%-14.29%). The incidence rate of influenza was 6.92% (95%CI: 5.53%-9.03%) with high incidence rates of 32.98% (95%CI: 26.36%-43.06%) and 21.66% (95%CI: 17.36%-28.37%) observed in the 0-4 years old group and 5-14 years old group, respectively. Conclusions Seasonal influenza brought substantial burden on health service in Beijing during the 2017-2018 influenza season, especially among children aged 0-4 and 5-14 years old. It is necessary to optimize the influenza vaccine coverage for both groups of children. Key words: Influenza; Multiplier model; Infection rate; Incidence rate