Characteristics of the human adenovirus infections from influenza-like illness samples in Xi′an

Objective To analyze the epidemiological characteristics and the molecular types of human adenovirus (HAdV) from influenza-like illness (ILI) samples with negative influenza virus in Xi'an from January 2013 to December 2015. Methods Samples from patients with ILI were collected from two national influenza sentinel surveillance hospitals during 2013—2015 in Xi′an. HAdV was detected by real-time PCR, and then the positive samples were inoculated into Hep-2 cells to isolate the viruses. The amplified products were purified and sequenced of hexon gene, and the sequences were compared with the Genebank data and phylogenetic trees were constructed. Results In 2367 samples, 88 samples were positive for HAdV, the positive rate was 3.72%. There were 7 subtypes detected, and the rates of each subtype are as follows: HAdV-1 was 9.09%, HAdV-2 was 22.73%, HAdV-3 was 23.86%, HAdV-4 was 5.68%, HAdV-5 was 7.95%, HAdV-6 was 3.41% and HAdV-7 was 1.14%. Males had higher infection rate than females, but there was no significant difference. The patients were divided into 6 groups according to age. There were 3 positive samples among those under 1 year of age, 36 positive samples among those 1 to 3 years old, 26 positive samples among those 4 to 6 years old, 16 positive samples in those 7 to 18 years old, 5 positive samples in 19 to 59 years old and 2 positive samples in those older than sixty years of age. HAdV infection was primarily confined to children under 7 years of age. Conclusions HAdV-3 and HAdV-2 were the dominant epidemic strains during 2013—2015 in Xi′an. Children younger than 7 years were the main susceptible population. HAdV infections circulate all year-round and there was no considerable seasonal variation. Key words: Human Adenovirus; Epidemiological characteristics; Molecular typing