RESUMEN
Objective:To investigate the epidemiological characteristics of influenza-like illnesses (ILI) and the etiological characteristics of influenza viruses in Minhang District of Shanghai from 2010 to 2021.Methods:The surveillance data collected by influenza surveillance sentinel hospitals and the influenza laboratory network from the first week of 2010 to the 52 nd week of 2021 were used for a statistical analysis. Results:A total of 122 903 cases with ILI were reported by the national influenza surveillance sentinel hospitals in Minhang during 2010 to 2021, and the average percentage of ILI cases was 0.94%, showing an increasing trend ( P<0.001). Among them, those aged 0-4, 5-14, 15-24, 25-59 and ≥60 years accounted for 4.35%, 13.30%, 14.30%, 54.32% and 13.73%, respectively. The percentage of ILI showed obvious periodicity. The seasonal incidence of ILI peaked from December to February and from July to September. But the winter peak at the beginning of 2013 was postponed. There was no significant peak in 2021. A total of 11 625 samples were tested from 2010 to 2021, in which the detection rate of influenza viruses was 20.92% (2 432/11 625). The positive rate was 12.83% (1 492/11 625) for influenza A viruses and 8.09% (940/11 625) for influenza B viruses, indicating that the epidemic intensity caused by influenza A viruses was greater than that caused by influenza B viruses. The overall positive rates for influenza A/H3N2 virus, influenza A/H1N1 virus, influenza B/Victoria lineage and influenza B/Yamagata lineage were 9.04% (1 051/11 625), 3.79% (441/11 625), 2.69% (313/11 625) and 2.19% (255/11 625) during 2010 to 2021. The predominant circulating strains altered between influenza A and influenza B viruses in Minhang District of Shanghai during 2010 to 2019. It generally took six months for an epidemic strain to be replaced by a new one. No obvious regularity was observed in 2020 or 2021. The tendency of the incidence of ILI reported from 2010 to 2019 was basically the same as that of the positive rate of influenza viruses, while there were significant differences in 2020 and 2021. Conclusions:Influenza viruses circulated seasonally in Minhang District of Shanghai with alternating prevalent viral subtypes and the infections mostly occurred in the winter and summer seasons. During the epidemic of COVID-19, the intensity of influenza was decreased, but with the normalization of prevention and control measures, the influenza epidemic showed an obvious upward trend. Therefore, it was important to strengthen the prevention and monitoring of influenza and analyze the virus variations in time.