To date, 79 HAdV types have been identified and are classified into seven species (A-G). [8] [9] [10] [11] [12] [13] [14] HAdV types 1 to 7 account for approximately 80% of all HAdV-infected cases in children. 5, 6, 15, 16 HAdV-3 and HAdV-7 are closely associated with LRTIs. 5, 6, 15, 16 HAdV-7 may lead to severe respiratory tract infections and HAdV-7 infection is associated with a high incidence of death and severe sequelae. [16] [17] [18] The dominant type and detection rate of HAdV vary in different countries and eras. Epidemic outbreaks of HAdV-3 and HAdV-7 infections occurred in children during the 1950s and 1960s in China. 16, 17 HAdV-3 and HAdV-7 infections are currently the most severe infections in Northern China with mortality rates of 16.6% to 33 .3%. The incidence and severity of HAdV infections have decreased gradually since the 1980s, 16, 17, 19, 20 although an epidemic outbreak of HAdV-7 infection occurred in a northern city of Shanxi Province (China) in January 2009. 19 Subsequently, an epidemic outbreak of HAdV-55 infection, which was confirmed to be an intertypic recombinant virus according to complete genomic sequencing and was designated as a new genotype after bioinformatics analysis, was detected in January 2013 in China. 21 
The study protocol was approved by the Ethical Review Committee of Hunan People's Hospital. The parents or guardians of all the participants in this cooperative study provided written informed consent. ALRTIs were diagnosed on the basis of clinical and radiologic findings.
Enrollment of children in the study followed the diagnosis of dominant symptoms of an acute or worsening cough or a clinical presentation that suggested an LRTI with a duration of less than or equal to 28 days. The age of the children in our study ranged from 1 day to 14 years.
All nasopharyngeal aspirate (NPA) samples were collected 1 to 3 days after admission to the hospital. Approximately 1 to 2 mL of deep NPA samples was obtained using a disposable sterile suction tube that was Figure 1 ).
The general demographics, including age, sex, and NPA sample collection time, were recorded. The details of the clinical findings and disease severity were obtained from the medical records after the patients' discharge from the hospital. Patients coinfected with bacteria, mycoplasma, and chlamydia were excluded from the statistical data of the clinical profiles of HAdV infection cases. 
Nested polymerase chain reaction (PCR) and DNA sequencing of the HAdV hexon gene HVR1-6 were used in the current study as they are more rapid and efficient compared with classical serologic testing. 23 [27] [28] [29] (Figure 1 ). 
Normally distributed continuous data are presented as the mean ± SD and were analyzed using the Student t test or ANOVA followed by Tukey's post hoc test, as appropriate. Non-normally distributed continuous data are presented as the medians (interquartile range) and were analyzed using the Mann-Whitney U test. Categorical data are expressed as frequencies and were analyzed using the χ 2 test or Fisher exact test, as appropriate. Multivariate logistic regression analysis was performed to identify independent risk factors. All analyses were performed using SPSS 20.0 (IBM, Armonk, NY). P < 0.05 was considered to be statistically significant. females (male/female, 1.81/1). Patient age ranged from 1 day to 168 months old (Supporting Information Figure 2 ). There were 197 patients with acute bronchitis, 1003 with bronchiolitis, and 3551 with pneumonia. Infections of other types were only sporadic (Supporting Information Table 1 ). Outcome LOS, median (IQR), d 5 (6-8) 6 (5-7.75) 7 (6-9.5) 9 (7-11) 6 (6-7.75) 8 (6.75-10) 7 (6-10) than the 11.6% (5 of 43 patients) of patients infected with the single HAdV-3 (P = 0.031; Table 4 ). Pneumonia consolidation and admission to the ICU were more common in patients with a single HAdV-7 infection (P = 0.013 and 0.019, respectively; Table 4 ). HAdV-7 infection resulted in patients having a longer hospital stay compared with that of patients infected with HAdV-3 (P = 0.03; Table 4 ).
The other respiratory viruses detected in patients infected with
HAdV are shown in Figure 30 and in 2011 in Taiwan. 31 Age is a known risk factor for LRTIs caused by HAdV. Most studies have indicated that HAdV is the major pathogen that causes LRTIs in children aged 6 months to 5 years old. 32 Severe LRTIs often occur in infants aged 6 to 24 months old. Children less than 6 months old often show immunity to HAdV because of maternal antibodies. 3, 5, 6, 16, 20 This study also indicated that the majority of HAdV infections occurred in patients from 6 months to 5 years old, whereas the HAdV detection rate was higher in children aged 3 to 4 years.
The reason for this difference may be the close contact of kindergarteners between the ages of 3 to 4 years. However, HAdV infection was most common in children aged 0 to 12 months old in Southern Palestine 33 and 6 to 23 months old in Korea. 6 HAdV infection was sporadically found throughout the year, and its incidence was relatively higher in winter and spring. 6, 16, 20 However, in the current study, the highest HAdV detection rate HAdV infection was more frequent in males. 23 In this study, the 14 HAdV types were not evenly distributed during the study period. The distribution of HAdV types attained epidemic proportions, lasting 2 or 3 years in each cycle. 6, [34] [35] [36] HAdV-3 and HAdV-7 infections were the major prevalent HAdV infections among hospitalized children in Hunan (Southern China), similar to reports from Korea, 6 Argentina, 34 and Chongqing (China), 15, 16 but in contrast to reports from Malaysia, 37 Israel, 38 and HAdV-41 were rarely observed in children, 39 which was consistent with the current study.
Gene recombination plays an important role in the molecular evolution of HAdV and can lead to a novel type with epidemic outbreaks or dominant substitutions, such as HAdV-55. HAdV-55 is an intertypic recombinant virus of HAdV-11 and HAdV-14 and was recently described by complete genomic sequencing and designated as a new genotype after bioinformatics analysis. 22 We also found that Additional multicenter studies are needed to establish the epidemiology of HAdV.
In conclusion, this study revealed the HAdV types and epidemiology of HAdV among hospitalized children in Hunan 