Epidemiological and immunological insights into respiratory infections in post-COVID-19.

Introduction: Post-COVID-19 respiratory infection dynamics require updated epidemiological characterization to inform clinical surveillance and public health strategy. Methods: We analyzed 2484 patients with respiratory tract infections (September 2023-February 2024) using comprehensive pathogen screening (29 viral, bacterial, and atypical targets) and cytokine quantification (12 cytokines). Results: Overall pathogen detection was 70.73%, with viral and bacterial identification in 40.42%(1004/2484), 51.45%(1278/2484) of cases respectively, and co-infections in 31.88% (predominantly Haemophilus influenzae-virus). Pediatric patients (<18 years) showed significantly higher positivity (74.1% vs. 63.2%, P < 0.05) with viral predominance (41.57% vs. 37.84%), while adults showed bacterial predominance (57.38% vs. 38.23%). Pneumonia risk exhibited age-pathogen specificity: Mycoplasma pneumoniae posed the highest risk in children (41.1% pneumonia rate) versus influenza B in adults (10.2% detection rate). Retrospective cytokine analysis (pre-pandemic 2018-2019 vs. post-pandemic 2023-2024) revealed post-pandemic suppression of IL-6 (6.12 vs.3.82 pg/mL) and IL-8 (37.98 vs. 18.35 pg/mL), with resurgence in 2024, particularly in pediatric and pneumonia cases (P<0.05). Discussion: Post-pandemic respiratory pathogen epidemiology is characterized by heightened pediatric susceptibility to viral co-infections, bacterial pathogen persistence despite control measures, and dysregulated inflammatory responses. These findings warrant age-stratified diagnostic and surveillance approaches with adaptive public health strategies to reduce respiratory infection morbidity.