ObjectiveTo analyze the surveillance status of acute respiratory tract infection pathogens in Fengxian District of Shanghai, and to determine the pathogen spectrum and epidemiological characteristics of acute respiratory tract infection in the district. MethodsCase surveillance data from Fengxian Central Hospital were collected through the Shanghai Integrated Surveillance System for Acute Respiratory Infections, and respiratory specimens were collected from the 50^th week of 2022 to the 49^th week of 2023 for nucleic acid detection of 25 pathogens and bacterial culture testing. Case surveillance data from Fengxian Central Hospital were collected through the National Influenza Sentinel Surveillance System, and respiratory specimens were collected for nucleic acid detection of 5 pathogens. ResultsThe percentage seeking for medical visits of influenza-like illness (ILI) and severe acute respiratory infection (SARI) were 4.74% and 0.81%, respectively, with epidemic peaks in winter and spring. A total of 1 610 samples were detected, among which 354 were SARI cases, whose age of P₂₅ and P₇₅ quartiles were 44 years and 71 years, respectively, with a positive detection rate of 48.31%. Among the 1 256 ILI cases, the age of P₂₅ and P₇₅ quartiles were 21 years and 39 years, respectively. The positive detection rate of pathogens was 65.04% in 123 ILI cases under comprehensive surveillance of respiratory tract infection and 66.11% in 1 133 ILI cases under influenza surveillance. The positive rates of influenza andSARS-CoV-2 in SARI samples were 12.99% and 29.66%, respectively. The positive rates of influenza and SARS-CoV-2 in ILI case samples were 33.20% and 31.53%, respectively. Influenza virus concentrated in the winter and spring. The ILI and SARI cases had the highest positivity rates in the 6‒14 years old group and 15‒24 years old group, respectively. ConclusionThe main pathogens of respiratory tract infection in Fengxian District of Shanghai were SARS-CoV-2 and influenza virus. Special efforts should be made to monitor respiratory disease pathogens in the population under 24 years old, and surveillance of SARI cases aged ≥60 years should be strengthened. The influenza virus and SARS-CoV-2 are alternating, which is different from the past and requires a change in the previous prevention and control strategies.

ObjectiveTo understand the epidemiological distribution and gene evolutionary variation of influenza A (H3N2) viruses in Fengxian District, Shanghai, in the surveillance year of 2023, and to provide a reference basis for influenza prevention and control. MethodsThe prevalence of influenza virus in Fengxian District in the 2023 influenza surveillance year (April 2023‒March 2024) was analyzed. The hemagglutinin (HA) gene, neuraminidase (NA) gene, and amino acid sequences of 75 strains of H3N2 influenza viruses were compared with the vaccine reference strain for similarity matching and phylogenetic evolutionary analysis, in addition to an analysis of gene characterization and variation. ResultsIn Fengxian District, there was a mixed epidemic of H3N2 and H1N1 in the spring of 2023, with H3N2 being the predominant subtype in the second half of the year, and Victoria B becoming the predominant subtype in the spring of 2024. A total of 75 influenza strains of H3N2 with HA and NA genes were distributed in the 3C.2a1b.2a.2a.2a.3a.1 and B.4 branches, with overall similarity to the reference strain of the 2024 vaccine higher than that of the reference strain of the 2022 and 2023 vaccine. Compared with the 2023 vaccine reference strain, three antigenic sites and one receptor binding site were changed in HA, with three glycosylation sites reduced and two glycosylation sites added; where as in NA seven antigenic sites and the 222nd resistance site changed with two glycosylation sites reduced. ConclusionThe risk of antigenic variation and drug resistance of H3N2 in this region is high, and it is necessary to strengthen the publicity and education on the 2024 influenza vaccine and long-term monitoring of influenza virus prevalence and variation levels.