Publication date: Mar 21, 2025

We report on the surge in human adenovirus (HAdV) cases in China starting in October 2023 and analyze the key drivers behind this increased circulation in the post-COVID-19 period. We analyzed targeted next-generation sequencing (tNGS) data from 1,875,862 hospitalized acute respiratory infection (ARI) cases across 4,758 hospitals in 314 cities throughout all 31 provinces of mainland China. An in-house script was used to analyze the positivity rates of different HAdV species nationwide and across various provinces. We also assessed the age-specific infection risk for HAdV species B and C using restricted cubic splines (RCS), and we tested differences in HAdV infection rates between vacation periods and school terms using the Kruskal-Wallis test. We identified an increased prevalence of HAdV species B replacing circulating species C, and this increase was associated with elevated HAdV activity in China from October 2023 to August 2024. Age-specific analysis indicates that, compared to HAdV species C, HAdV species B has a higher infection rate in school-aged children. Comparison of HAdV incidence rates during school terms and vacations showed that schools are the primary transmission setting for HAdV species B. These findings strongly support the conclusion that school-associated cluster infections caused by HAdV species B are the drivers of the ongoing increased circulation of HAdV in China. This study found that changes in susceptible populations and transmission settings due to an increased prevalence of HAdV species B were the key factors driving the elevated HAdV activity in China starting in October 2023.

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