[Epidemiological characteristics of respiratory multi-pathogen co-detection among influenza-like illness cases in...

Objective: To analyze the epidemiological characteristics of respiratory multi-pathogen co-detected in China during the 2023-2025 surveillance years based on influenza-like illness (ILI) surveillance data, and to characterize the distribution across populations, temporal periods, regions, and pathogen types. Methods: Data were obtained from the respiratory multi-pathogen surveillance of ILI outpatients and emergency department visits across 216 national sentinel hospitals within the National Acute Respiratory Infectious Disease Sentinel Surveillance Network from week 42 of 2023 to week 14 of 2025. Given that the surveillance spanned two distinct phases, the impact of adjustments to the surveillance protocol was evaluated. Descriptive epidemiological methods were employed to analyze the patterns of multi-pathogen co-detections. Results: A total of 175 131 ILI cases were tested during the 2023-2025 surveillance years, with an overall multi-pathogen co-detection rate of 17.99%. The predominant co-detection combination was "virus+bacteria" (66.64%), commonly involving influenza virus or rhinovirus paired with Streptococcus pneumoniae or Haemophilus influenzae. Significant differences in co-detection rates were observed across different age groups, genders, and occupations (all P<0.001). Regarding the population distribution, the highest rates were found in school-aged children (5-14 years, 26.62%) and infants/toddlers (0-4 years, 25.83%). Males (19.57%) exhibited a higher detection rate than females (16.39%). Temporally, the co-detection rate peaked during the winter and spring seasons. Spatially, South China exhibited the highest age-standardized co-detection rate (23.74%), while Northeast China reported the lowest (12.72%). Southern regions were characterized by prolonged circulation, whereas northern regions displayed short-term epidemic patterns. Conclusions: Multi-pathogen co-detections were prevalent in China during the 2023-2025 surveillance years, characterized by a distinct clustering in younger age groups and a "high in the south, low in the north" geographic trend. Synergistic co-detection of viruses and bacteria remains the primary manifestation. It is recommended to strengthen multi-pathogen surveillance and data analysis in high-prevalence regions and among school-aged populations, and to implement differentiated prevention and control strategies tailored to regional seasonal characteristics.