Acute respiratory tract infections (ARTIs) remain a major global health burden. Southwest China, with its complex geography and climate, represents a critical region for respiratory pathogen ecology. This study aimed to characterize the epidemiological dynamics of nine respiratory pathogens among ARTI patients in Southwest China across the pre-COVID-19 period (January 2019 to December 2019), the COVID-19 non-pharmaceutical interventions (NPIs) period (January 2020 to December 2022), and the post-NPIs period (January 2023 to December 2023). A multicenter, retrospective study was conducted from January 2019 to December 2023, including 240,611 ARTI patients. Serum IgM antibodies against nine pathogens: Influenza A virus (FluA), Influenza B virus (FluB), Respiratory syncytial virus (RSV), Parainfluenza Virus (PIV), Adenovirus (ADV), Mycoplasma pneumoniae (MP), Chlamydia pneumoniae (CP), Legionella pneumophila (LP), and Coxiella burnetii (Q fever, QF) were detected by indirect immunofluorescence assay, and the findings were interpreted as serological positivity/recent exposure signals rather than definitive microbiological confirmation of acute infection. Epidemiological characteristics and temporal trends were analyzed using descriptive statistics and Join-Point regression. Monthly serological positivity rates showed a marked decline during the early phase of the NPIs period. However, the overall serological positivity rate surged to 30.07% in the post-NPIs period, significantly higher than the pre-COVID-19 (27.83%) and NPIs (27.87%) periods ( p < 0.001). MP showed the highest serological positivity signal across all study periods. Pathogen responses diverged: FluB remained suppressed (declining to 0.58% in the post-NPIs period), whereas FluA and RSV resurged significantly. Children aged 28 days-4 years accounted for 49.56% of the cohort, indicating a predominantly pediatric testing population. The median age among serologically positive cases increased for several major pathogens, for example, FluA from 3 to 6 years and RSV from 0 to 2 years, despite higher pediatric susceptibility. Serological co-detection rates increased from 4.05% to 4.86% with a predominant shift from FluB-MP to PIV-MP. Join-Point analysis confirmed a sharp decline of FluB and a sustained increase of PIV in the NPIs period. The NPIs were associated with substantial shifts in the serological positivity patterns of respiratory pathogens in Southwest China. While serology alone is insufficient to define the full complexity of acute respiratory pathogen ecology, these findings should be interpreted as serological exposure patterns rather than confirmed acute infections, and they provide a unique, large-scale sero-epidemiological map of recent exposure dynamics that serves as a valuable baseline for future molecular surveillance. Clinical trial number: Not Applicable.
Zeng et al. (Tue,) studied this question.