Characteristics of influenza virus epidemic in Yiwu City,Zhejiang Province from 2017 to 2022
[Objective]To investigate the epidemiological trends of influenza in Yiwu City,Zhejiang Province from 2017 to 2022,and to provide references for local adjustments to influenza prevention and control strategies.[Methods]Real-time fluorescence quantitative PCR was used to detect and type influenza viruses in nasal and pharyngeal swab specimens of the patients with influenza-like illness(ILI).The results were statistically analyzed.[Results]From 2017 to 2022,a total of 106 661 ILI cases were reported in Yiwu City,with annual reported cases of 31 273,33 522,20 090,9 965,3 202,and 8 609,respectively.The majority of ILI cases were in the age group of≤14 years,accounting for 89.16%.A total of 6 893 specimens were collected and tested,of which 945 were tested positive for influenza virus nucleic acid,with an overall positivity rate of 13.71%.The dominant subtypes were H3N2 and B-Victoria,accounting for 40.63%(384/945)and 35.03%(331/945)respectively.The highest positivity rate was in 2019,at 25.19%(265/1 052).The positivity rates significantly decreased in 2020 and 2021,to 5.74%(66/1 149)and 5.77%(75/1 300),respectively.The rate increased in 2022 to 13.85%(180/1 300).The highest proportion of A/H3N2 positivity was in 2017,at 69.14%(168/243).The highest proportion of A/H1N1 positivity was in 2018,at 50.86%(59/116).The highest proportion of B/Victoria positivity was in 2021,at 100.00%(75/75).The highest proportion of B/Yamagata positivity was in 2018,at 5.17%(6/116).[Conclusion]Influenza in Yiwu City exhibits obvious seasonal patterns,with two peaks in winter-spring and summer.Dominant strains such as A/H3N2,B/Victoria,and A/H1N1 alternate or co-circulate.During the COVID-19 pandemic,seasonal influenza significantly decreased,and a series of prevention and control measures had a positive effect on influenza prevention and control.
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