Characteristics of respiratory co-infections in influenza-like illness during the post-COVID-19 era.

BackgroundIn the postpandemic era, populations may experience an "immunity debt" due to reduced social interactions. Studying respiratory co-infections in populations is of great significance for precise treatment and the prevention and control of infectious disease outbreaks.MethodsA prospective surveillance network was established across 24 sentinel hospitals. Respiratory specimens were collected. Nucleic acids were extracted using magnetic bead-based methods and tested by real-time PCR for 10 viruses and 5 bacterial targets. Data were analyzed to determine positivity rates, co-infections, and age-specific patterns using Join-Point Regression.ResultsThe overall pathogen positivity rate was 64.3% (9954/15,481). Co-infection with ≥2 pathogens was detected in 26.7% of patients. Influenza virus (IFV) was the predominant virus (20.9% overall), peaking in January 2025 (49.4%). Human metapneumovirus was the second most common virus (8.0%). Haemophilus influenzae (21.1%) and Streptococcus pneumoniae (17.7%) were the most frequently detected bacteria. Positivity rates exhibited significant age-related variation. Join-Point analysis revealed that the IFV positivity rate increased until age 50. Considerable geographic variation was observed, with the total positivity rate ranging from 53.2% to 82.2% across different cities.ConclusionThis comprehensive surveillance revealed a high burden of respiratory pathogens and complex co-infection patterns in the postpandemic era.