Estimates of influenza-associated excess numbers of influenza-like illness cases in Changping district, Beijing, 2012-2017

Abstract

Objective To estimate the excess numbers of influenza-like illness (ILI) cases associated with influenza from 2012 to 2017 in Changping district. Methods The surveillance data of ILI cases from secondary medical institutions and above in Changping district was collected to estimate influenza-associated excess numbers of ILI cases in different age groups using Serfling regression model and the adjusted Serfling regression model, respectively. Results The epidemic weeks of influenza were 52nd-2nd in 2012-2013, 52nd-6th in 2013-2014, 46th-3rd in 2014-2015, 52nd-14th in 2015-2016 and 47th-6th weeks in 2016-2017. The average number of annual influenza epidemic weeks was 10 (range: 4-15). The corresponding excess numbers of ILI cases attributed to influenza were 598 (95%CI: 207-719), 1 517 (95%CI: 1 070-1 964), 2 883 (95%CI: 2 243-3 522), 5 027 (95%CI: 4 067-5 986) and 3 126 (95%CI: 2 291-3 961) respectively. The average annual excess numbers of ILI cases were 2 630 (95%CI: 1 976-3 230) by the adjusted Serfling regression model, accounting for 57.6% of total ILI cases surveyed over the same period. Serfling regression model showed that the estimated results in age groups of less than 5 years old, 5-59 years old as well as in the whole population were consistent with the adjusted Serfling regression model. Conclusions The adjusted Serfling regression model was more accurate than the traditional Serfling regression model. The annual epidemic of influenza resulted in thousands of and tens of thousands of excess ILI cases and outpatient visits in Changping distirct. Key words: Influenza; Regression analysis; Population surveillance; Excess numbers of influenza-like illness cases