Molecular Epidemiology of Pediatric Respiratory Adenovirus Infections in Île-de-France: Findings from Whole-Genome Sequencing

Background Human adenoviruses (HAdVs) are a frequent cause of respiratory tract infections in children; however, their epidemiological patterns and genomic diversity remain insufficiently characterized in Europe. As respiratory HAdVs can cause outbreaks of acute and severe disease and show periodic re-emergence, improved understanding of their circulation is needed. Aim To investigate the epidemiology, age distribution, and genomic diversity of respiratory HAdVs in pediatric patients in Île-de-France during the first half of 2022. Methods We retrospectively analyzed 6,956 respiratory samples from patients <18 years, collected at five hospitals (Jan–June 2022). HAdVs were detected by multiplex PCR. Viral loads were quantified in mono-infections, and whole-genome sequencing was performed on samples with sufficient viral load. Results HAdVs were detected in 14% of samples, making them the second most prevalent virus after rhinovirus/enterovirus. Co-infections were frequent (64%), particularly in younger children. Among the 254 mono-infected samples with viral-load quantification, 110 (43%) had low or undetectable viral loads. WGS of 122 samples revealed HAdV species B (62.3%), C (34.4%), and F (3.3%). Species distribution varied by age: HAdV-C predominated in children under 2 years, while HAdV-B was more common in older children. The most frequent genotypes were B3 (76.3%), B66 (18.4%), and B7d (5.3%) within species B, and C1 (33.3%), C89 (26.2%), and C2 (23.8%) within species C. Conclusion HAdVs are prevalent among children with respiratory infections, with age-specific patterns and substantial genomic diversity. The circulation of diverse genotypes, including recombinants and potentially more virulent variants, highlights the importance of sustained molecular surveillance.