1.Characteristics of influenza virus epidemic in Yiwu City, Zhejiang Province from 2017 to 2022
Buqing CHEN ; Bo CHEN ; Junfang LOU ; Jinhua CHEN
Shanghai Journal of Preventive Medicine 2024;36(7):712-715
ObjectiveTo 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. MethodsReal-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. ResultsFrom 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). ConclusionInfluenza 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.