Background: Human adenovirus 55 (HAdV-55) has caused recent outbreaks of acute respiratory disease (ARD) among adults and military trainees. The active surveillance for HAdV infections was sparse in China, and current knowledge on the HAdV-type distributions and its molecular evolution is lacking.

Objectives: To acquire better understanding on the prevalence and molecular evolution of HAdV-55 strains in China, for an informed strategy for disease control and prevention.

Population/methods: Nasopharyngeal aspirates were collected from hospitalized children with ARTI in Chongqing during 2009-2012. The genotype of HAdV isolates were determined by sequencing the partial hexon and fiber genes. Whole genome sequences of HAdV-55 were obtained for molecular evolution analysis.

Results: About 191 (8·55%) HAdV were detected in 2234 children, including 92 (48·2%) with HAdV-7, 72 (37·7%) with HAdV-3, 6 (3·1%) with HAdV-55, 5 (2·6%) with HAdV-5, 4 (2·1%) with HAdV-1, 1 (0·5%) with HAdV-2, and 11(5·8%) with untyped HAdV. Four of these children developed pneumonia, two of whom were diagnosed with severe pneumonia and/or encephalopathy. HAdV-55 isolates clustered with HAdV-11 sequences based on the hexon gene and clustered with HAdV-14 sequences based on the fiber gene and the whole genome. The overall evolutionary rates of hexon gene, fiber gene, and whole genome of HAdV-55 were estimated at 6·2 × 10(-5) s/s/y, 8·0 × 10(-5 ) s/s/y, and 1·7 × 10(-5) s/s/y, respectively.

Conclusions: This study suggested HAdV-55 as an emerging infectious disease pathogen has conserved genetic structure and is closely related to each other. Further molecular investigation based on HAdV-55 of wider origin might facilitate understanding its diversity, dissemination, and transmission in China.