First detection of human adenovirus type 7 deletion mutant associated with an outbreak of acute respiratory infection.

backgroundHuman adenovirus B7 (HAdV-B7) has emerged as an increasingly important respiratory pathogen in recent years. Ten first grade students experienced symptoms of acute respiratory infection at a primary school in Beijing from November 13 to 21, 2024. We investigated the cause of this outbreak.

methodsIn partnership with the local center for disease prevention and control, we collected demographic information (age and gender) of the affected students and obtained pharyngeal swab specimens from six students. We used multiplex real-time PCR to screen for 22 common respiratory viruses in these samples. To isolate HAdV, Hep-2 cells were inoculated with HAdV-positive pharyngeal swab samples. Isolates were sequenced by Sanger and whole-genome sequencing. In addition, four HAdV-B7 strains isolated from 2024 to 2025 influenza-like illness surveillance cases were also sequenced as a control to determine whether the same mutations existed. The strains were characterized molecularly using gene homology analysis, recombination analysis and phylogenetic reconstruction.

resultsWe collected six pharyngeal swab samples from ten students based on consent. All samples were HAdV-positive as determined by multiplex real-time PCR. None of the students were co-infected with other viruses. We successfully isolated the HAdV strain from each student sample. Blast analysis and phylogenetic analysis of the hexon, penton, and fiber genes suggested that this outbreak was caused by HAdV-B7 (P7H7F7). A unique T335S mutation was identified within the RGD loop of the penton base in this outbreak. Whole-genome sequencing confirmed high sequence identity between our isolates and HAdV-B7 strains from multiple regions in China and abroad. In addition, all strains obtained in this outbreak had 57 nucleotides deletion in the E3 region. Interestingly, the same deletion mutants were also found in HAdV-B7 strains isolated from 2024 to 2025 influenza-like illness surveillance cases, indicating that this deletion mutation has been prevalent and may represent an established molecular signature of a circulating HAdV-B7 sublineage.

conclusionsWe report the first detection of a human adenovirus type 7 deletion mutant associated with an outbreak of acute respiratory infections in Beijing in 2024. This deletion mutation was prevalent and may represent an established molecular signature of a circulating HAdV-B7 sublineage. How this mutation affects viral pathogenicity remains unclear and needs further investigation. Our findings underscore the critical importance of implementing timely molecular surveillance for guiding outbreak control and informing prevention strategies against respiratory pathogens.