Study on seasonal characteristics and pathogenic distribution of influenza in Gansu province of China

Abstract

Objective: To study the epidemiologic characteristics of influenza in Gansu province of China and to optimize the related vaccination program. Methods: Weekly influenza surveillance data from the first week of 2010 to the fortieth week of 2016 were collected, in Gansu province. χ(2) test was used to compare the differences of nucleic acid positive rate and the virus types in the four seasons. Time series seasonal decomposition (TSSD) was used to explore seasonal patterns and characteristics of influenza epidemics in Gansu. Results: 59 791 specimens were tested, with 8 501 positive for influenza virus and positive rates as 14.22%. Types A(H1N1)pdm09, A(H3N2) and type B were accounted for 98.76% of all the positive specimens. Proportions of the positive rate of influenza virus appeared in spring, summer, autumn and winter were 15.12%, 0.98%, 4.02% and 24.26% respectively. The predominant type of virus in autumn and winter was A(H3N2), with B mainly in spring. Influenza in Gansu province showed typical single-peak type distribution, with epidemic peak appeared from December to next January. The type A(H3N2) related peak appeared the earliest, followed by A(H1N1) pdm09, with type B the latest. Conclusions: Peaks and the duration of influenza seasonal epidemics were related to the types of dominant strains. Annual influenza vaccination campaigns should start in October, to provide effective protection during the epidemic period.