Shifts in acute respiratory pathogen epidemiology: an 8-year surveillance study in Hangzhou, China (2018–2025)

Abstract

To analyze the epidemiological characteristics of six common respiratory pathogens in cases of Acute Respiratory Tract Infection (ARTI) in Hangzhou from 2018 to 2025, to provide a basis for clinical diagnosis and treatment, as well as public health prevention and control. A multicenter retrospective study was conducted. Data from 81,974 ARTI cases from seven medical institutions in Hangzhou City between January 2018 and December 2025 were collected. Cases with positive test results were analyzed for influenza A virus (FluA), influenza B virus (FluB), respiratory syncytial virus (RSV), adenovirus (ADV), Mycoplasma pneumoniae (MP), and Chlamydia pneumoniae (CP), and statistical analysis was performed according to the pandemic stage, age, sex, season, and co-infection status. Among 81,974 patients, a total of 33,350 cases tested positive for pathogens, with an overall positive rate of 40.68%. MP (19.56%) and FluA (16.93%) were the most prevalent pathogens. The positivity rates of each pathogen showed statistically significant differences across the three stages before, during, and after the Coronavirus Disease 2019 (COVID-19) pandemic (all P < 0.001). Compared with the pre-COVID-19 pandemic period (2018–2019), the positive rates of FluA, FluB, and MP were significantly suppressed during the COVID-19 pandemic period (2020–2022), and then experienced a sharp “revenge rebound” in the post-COVID-19 pandemic period (2023–2025) (for example, the positive rate of MP rebounded from 5.43% to 21.09%). In contrast, the positive rates of RSV, ADV, and CP showed a persistent state of inhibition, but the absolute number of cases far exceeded that of before the COVID-19 pandemic. MP had the highest infection rate among 6– < 12 years old (38.31%), whereas FluA was more common in adults. The epidemiological distribution showed obvious seasonal heterogeneity: FluA/FluB/RSV were more prevalent in winter, MP was active in autumn, and ADV was more prevalent in summer. The co-infection rate was 7.22% (5,922 cases), and the most common combination was FluA + MP, accounting for 53.82% of all co-infections. From 2018 to 2025, the pathogen spectrum of ARTI in Hangzhou was mainly composed of MP and FluA. The COVID-19 pandemic and related non-pharmaceutical interventions (NPIs) have had a profound and heterogeneous impact on the epidemic pattern of respiratory pathogens. FluA, FluB, and MP showed the characteristics of “suppression-retaliatory rebound.” In the post-COVID-19 pandemic era, the activity of pathogens has clear seasonal, age, and gender distribution patterns, and the rate of mixed infections is high. The research results suggest that a dynamic monitoring system needs to be established, and targeted prevention and control measures should be implemented for key individuals and pathogens during high-incidence seasons.