Epidemiological characteristics of influenza viruses at subtypes/lineages level in Jiangsu, 2011–2019

  Objective  To understand the differences in epidemiological characteristics of influenza viruses of different subtypes/lineages in Jiangsu province from 2011 to 2019 and provide evidences for the precise prevention and control of influenza.

  Methods  Laboratory-confirmed influenza cases reported in influenza surveillance system in Jiangsu from January 2011 to December 2019 were analyzed. The differences in distribution of categorical variable data were compared with χ² test, the risk factors were identified with Logistic regression analysis and odds ratios were calculated.

  Results  There were 26 934 confirmed influenza cases with subtype/lineage testing results in Jiangsu during this period. Influenza A (H3) virus accounted for the highest proportion (40.40%). The proportion of influenza subtypes/lineages differed significantly with year and area ( χ²=12448.182, P<0.001; χ²=180.333, P<0.001). The seasonal peaks were observed during December-January and August-September for A (H3) virus, during January-February for A(H1) virus and B-Y virus, during March-April for B-V virus. The proportion of influenza subtypes/lineages differed significantly among age groups and occupation groups ( χ²=13588.399, P<0.001; χ²=70.724, P<0.001). Multivariate logistic regression analysis showed that, after adjustment for areas and months, children aged <5 years were more likely to be infected with A(H1) virus. Older children aged 6–15 years had a significantly increased risk for the infection with B-V virus, while the elderly (more than 65 years) were prone to be infected with A (H3) virus and B-Y virus.

  Conclusion  In Jiangsu, influenza viruses of different subtypes/lineages circulated alternatively, they have different seasonality and infection risks. It is essential to analyze the epidemiological characteristics of influenza viruses at subtypes/lineages level in time for the precise prevention and control of influenza.