Molecular and clinical characterization of human adenovirus type 21 (HAdV-21) associated with respiratory tract infections in hospitalized adults in Hangzhou, China, 2022-2024.

OBJECTIVES

Human adenovirus type 21 (HAdV-21) is linked to severe pneumonia in adults, but adult data from China remain scarce. This study compared the molecular and clinical features of HAdV-21 against other genotypes in hospitalized adults.

METHODS

We retrospectively analyzed adults with HAdV respiratory infections at a Hangzhou tertiary hospital (January 2022-August 2024). Genotyping utilized hexon gene sequencing. Clinical, laboratory, and etiological data were compared. Multivariable logistic regression identified independent risk factors for severe illness.

RESULTS

Among 75 genotyped cases, HAdV-21 was the most prevalent (38.7%; comprising 21a and 21b strains). Compared with other genotypes, HAdV-21 infection was associated with distinctive respiratory findings like dyspnea (62.1% vs. 19.6%). Laboratory abnormalities, like lymphocyte percentage (9.70% vs. 18.55%), PCT (0.48 vs. 0.13 ng/mL), and organ injury markers AST (32.00 vs. 19.00 U/L), were also more frequent in the HAdV-21 group. Severe illness (41.4% vs. 13.0%) and respiratory failure (34.5% vs. 6.5%) were significantly more common in the HAdV-21 group, along with a higher rate of coinfection. Overall multivariable analysis identified HAdV-21 (aOR 5.44, 95% CI 1.32-22.48) and older age (aOR 1.05 per year, 95% CI 1.01-1.09) as independent risk factors for severity. However, this association for HAdV-21 was not significant in the subgroup of patients with adenovirus mono-infection.

CONCLUSION

HAdV-21 emerged as the predominant genotype among these hospitalized adults, associating with increased severe disease and respiratory failure. Importantly, this severity appears largely mediated by higher coinfection frequencies rather than HAdV-21's inherent viral pathogenicity alone.