A comprehensive analysis of molecular epidemiology and clinical characteristics of human adenovirus among hospitalized children with pneumonia in Tianjin, China, 2022–2025

Human adenoviruse (HAdV) is a major pathogen associated with acute respiratory infections (ARIs) in children worldwide. However, the epidemiological and genotypic characteristics of HAdV among pediatric inpatients with ARIs have not been fully elucidated in Tianjin. Therefore, this study aimed to examine the epidemiological features, genotype distribution, and clinical associations of HAdV infection in this population. Respiratory specimens were collected from children hospitalized with ARIs between September 2022 and August 2025. Targeted next-generation sequencing was used for initial screening and typing of HAdV. Randomly selected positive samples were further analyzed by conventional PCR amplification targeting the hexon gene, followed by phylogenetic analysis using reference sequences from GenBank. A total of 19,523 specimens were tested, yielding an overall HAdV detection rate of 8.7% (1,704/19,523). The detection rate was significantly higher in males than in females ( P = 0.002). Significant differences were observed across age groups ( P < 0.001), with the highest detection rate in the 3–6 years age group (11.9%, 551/4,611). Notably, genotype composition also differed significantly by age ( P < 0.001): preschool and school-aged children were mainly infected with HAdV-3 and HAdV-7, whereas infants and toddlers were predominantly infected with HAdV-3 and HAdV-1. HAdV was detected year-round with marked seasonal variation ( P < 0.001) and a clear peak in winter (13.4%, 573/4,285). Temporal analysis revealed a shift in predominant species: HAdV-C was dominant before August 2023, while HAdV-B became predominant thereafter. Seasonally, HAdV-B (particularly HAdV-3 and HAdV-7) was predominant in winter, whereas HAdV-C (particularly HAdV-1) was more common in summer ( P < 0.001). Among 1,447 successfully genotyped samples, 14 genotypes belonging to five HAdV species (A, B, C, E, and F) were identified. The predominant genotypes were HAdV-3 (51.5%, 745/1,447) and HAdV-7 (18.4%, 266/1,447), followed by HAdV-1 (12.2%, 177/1,447), HAdV-2 (6.6%, 95/1,447), HAdV-21 (6.3%, 91/1,447), HAdV-5 (2.4%, 35/1,447), HAdV-4 (1.3%, 19/1,447), and other genotypes (1.3%, 19/1,447). The main clinical diagnoses included pneumonia, bronchitis, tonsillopharyngitis, and upper respiratory tract infections (URTIs). Genotype–phenotype association analysis revealed that HAdV-3 and HAdV-7 were predominant in pneumonia cases, whereas HAdV-3 and HAdV-1 were common in tonsillopharyngitis and URTIs. Importantly, children infected with HAdV-7 were more likely to develop severe pneumonia ( P < 0.001). HAdV-3, HAdV-7 and HAdV-1 were the dominant circulating genotypes among hospitalized children with ARIs in Tianjin from 2022 to 2025. A higher detection rate was observed among male toddlers, with a winter peak. Age-specific, seasonal, and inter-annual shifts in genotype distribution were observed, with HAdV-B replacing HAdV-C as the dominant species after August 2023. These findings support region specific surveillance and targeted interventions, and provide epidemiological evidence to inform the rational design and formulation of multivalent vaccines against pediatric HAdV.