Comparison of Clinical Features and Severity of Subgroup A and B Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract disease. This study investigated the clinical differences between RSV subgroups A and B using data from a university-affiliated medical center in Taiwan from September 2018 to August 2023. RSV was confirmed via viral culture or rapid antigen tests, with peak circulation occurring from August to January. Among 152 RSV isolates, subgroup A (61.2%) was more common than subgroup B. Children aged ≥ 6 months had more frequent fever (94% vs. 67%), longer febrile duration (3 vs. 1 days), and more comorbidities (45% vs. 14%) than those < 6 months (all p < 0.001). Immunocompromised patients, primarily adults, had higher intubation rates and significantly greater mortality (27%), which occurred exclusively in this group. Compared to subgroup B, subgroup A was associated with higher fever incidence (91% vs. 75%, p = 0.005), longer fever (2 vs. 1 day, p = 0.03), higher CRP (1.2 vs. 0.3 mg/dL, p = 0.001), and more bacterial coinfection/co-detection (29% vs. 10%, p = 0.006). Five G protein substitutions, notably S283P, emerged after December 2022. New clades A.D.3.5, A.D.5, A.D.5.2, and B.D.E.1 were identified post-COVID, with B.D.E.1 linked to increased dyspnea. Ongoing surveillance is warranted to monitor emerging variants and guide preventive strategies in high-risk groups.