Epidemiological characteristics of influenza-like illness in Guizhou, 2018–2022

Objective To understand the epidemiological characteristics of influenza-like illness (ILI) in Guizhou province from 2018 to 2022 and the variation of influenza virus, and provide evidence for the effective prevention and control of influenza.

Methods Descriptive epidemiological method was used to analyze ILI surveillance data in Guizhou from 2018 to 2022.

Results The proportion of ILI medical visits (ILI%) in Guizhou Province during this period was 7.94%, and the ILI% increased year by year. The incidence of influenza showed peaks during winter,-spring and during summer-autumn. The top three prefectures (municipality) with the highest ILI% were Qiannan, Guiyang and Qiandongnan, and the ILI% was lowest in Anshun. Of the ILI cases, the proportion of children under 5 years old was highest, the proportion of people over 60 years old was lowest, and the differences in ILI case proportion among different age groups were significant (P<0.001). The positive rate of influenza virus nucleic acid was 11.37% in Guizhou during this period, and the predominant strains of influenza viruses alternated with years. The monthly positive rate of influenza virus nucleic acid was positively correlated with the ILI% (P=0.028). A total of 227 of influenza epidemics were reported in Guizhou during this period, and the epidemics mainly occurred in schools, and the main types of influenza viruses causing epidemics were seasonal influenza A (H3N2) virus, influenza B virus Victoria lineage and influenza A (H1N1) virus.

Conclusion The ILI% increased year by year in Guizhou from 2018 to 2022. After 2020, the positive rate of influenza virus nucleic acid decreased first and then increased, the different types of virus spread alternately, and the children under 5 years old were the key affected population. Health education and vaccination in children under 5 years old in schools should be strengthened.