Epidemiological Characteristics of Respiratory Syncytial Virus and Evolutionary Analysis of the G Gene in 2,892 Cases of Severe Acute Respiratory Infection

Objective To analyze the epidemiological characteristics and molecular evolution of the G gene of human respiratory syncytial virus (HRSV) in severe acute respiratory infection (SARI) cases in Beijing from 2017 to 2024, providing scientific basis for regional prevention and control strategies and immunization planning. Methods Respiratory specimens were collected from 2,892 SARI cases at two sentinel hospitals in Beijing from January 2017 to December 2024. HRSV detection and typing were performed using multiplex real-time fluorescent polymerase chain reaction (PCR). Descriptive epidemiological methods analyzed HRSV circulation patterns. For HRSV-positive specimens, the second hypervariable region of the G gene was amplified and sequenced using a one-step method. A phylogenetic tree was constructed using HRSV A and B subtype reference strains from the Global Initiative on Sharing All Influenza Data (GISAID) and GenBank databases. Amino acid homology, mutation sites, and N-glycosylation sites were analyzed to investigate HRSV genotype distribution and genetic evolution.Results From January 2017 to December 2024, 2,892 HRSV samples were collected from SARI cases, with 41 HRSV-positive detections yielding an overall detection rate of 1.42% (41/2,892). By age group, the highest detection rate was observed in the 2–<5 years group (5.37%, 11/205), followed by the 0–<2 years group (2.50%, 1/40) and the ≥60 years group (1.24%, 14/1,128); the lowest detection rate was in the 18–<60 years group (0.50%, 5/1,004) . Seasonal distribution from 2017 to 2024 showed winter as the peak season (2.90%), with summer having the lowest rate (0.15%). Monthly distribution from 2017 to 2024 revealed no HRSV detection during the autumn and winter of 2020. Detection peaks occurred in April (5.00%), September (4.35%), and December (4.55%) of 2021; The detection rate reached 4.76% in April 2022; it was 14.29% in June 2023, with the highest monthly rate of 6.48% occurring between November 2023 and March 2024. Eleven G gene HVR2 sequences were obtained: two A subtype sequences were both ON1 genotype, and nine B subtype sequences were all BA9 genotype. Subtype A isolates showed 96.25% nucleotide homology and 93.75% amino acid homology. Subtype B isolates exhibited nucleotide homology ranging from 93.84% to 99.42% and amino acid homology ranging from 86.79% to 99.06%. All subtype A strains exhibited a 23-amino acid insertion (positions 284–306) following amino acid 283 in the G protein, with this insertion sequence highly similar to positions 261–283. Subtype B strains showed a 20-amino acid insertion (positions 251–270) following position 250. Amino acid alignment revealed L274P, L297P, and Y303H mutations within the insertion region of A subtype strains. Among B subtype strains, some sequences (4/9) exhibited mutations at K256N and I268T sites. N-glycosylation site prediction indicated that both A subtype strains contained N108 and N140 sites; among the 9 B subtype strains, 4 contained all three sites: N233, N261, and N299.Conclusion The 2017–2024 HRSV circulation in Beijing exhibited distinct age and seasonal clustering. The ON1 and BA9 genotypes were the predominant genotypes for HRSV A and B subtypes, respectively. Characteristic insertions, mutations, and conserved glycosylation sites in the G protein suggest ongoing viral evolution and potential immune escape capabilities. Enhanced long-term molecular surveillance is warranted to support vaccine application and precision prevention and control.