Adenovirus infection in children with acute lower respiratory tract infections in Beijing, China, 2007 to 2012

HAdV is a significant causative agent of respiratory tract illnesses in both children and adults. Here, the molecular epidemiology and clinical features of HAdV associated pediatric ALRTIs in Beijing Children’s Hospital from March 2007 to December 2012 were described. Results showed that the HAdV infection rate in the current study population was 5.8 %, which was consistent with previous reports from China and other countries [22‐24]. Results showed that most patients with HAdV infection were younger than 5 years (88.35 %), which is similar to numbers reported in previous studies [1, 22, 23, 25‐27]. This may because the immune systems of young children are not well developed, which leaves them prone to more severe HAdV disease. This may also suggest that school-age children are exposed to the most common endemic types of HAdV early in life, thereby establishing a protective immunity resulting only in mild clinical symptoms, such that upper respiratory tract infection does not require care in an emergency department or hospital in this age group.

Over a period of 6 years, 11 different types of HAdV belonging to 4 species (HAdV-A, B, C, E) were identified in respiratory specimens from children with ALRTIs. HAdV-7 and HAdV-3 of species B comprised the most prevalent types and presented throughout the duration of the study. Although these results were consistent with previous reports from Korea and Argentina [22, 28, 29], investigations from Croatia, Peru, Canada, France showed that species C predominated [1, 25, 26, 30]. This difference in type prevalence may be attributed to difference in regions, year of study, and population recruited.

Notably, some newly emerging or re-emergent types or variants were here identified, although only in rare cases. Five patients were found to have HAdV-B55 (formerly named HAdV-11a), which is an uncommon re-emergent type that once caused an outbreak of respiratory tract infection in a senior high school in Shanxi Province, China in 2006, including one fatal case [15]. Subsequently, HAdV-B55 has been associated with several outbreaks of respiratory disease in other provinces in China [31]. An emerging variant, HAdV-B14p1 (formerly known as 14a), was also found. Recently, HAdV-B14p1 has been associated with several large outbreaks of acute respiratory infection, which included severe and even fatal cases in the United States and Europe [16, 32]. Additionally, in 2011, an outbreak of febrile respiratory illness that affected 43 students in Gansu Province, China was reported to be caused by HAdV-B14p1 [33]. One HAdV-B14 infected patient who presented with bronchopneumonia and required hospitalization in April 2010 was identified. By further sequencing the fiber gene (data not shown), this strain was confirmed to be HAdV-B14p1 because it contained a unique characteristic 6-nuleotid deletion in fiber knob region as reported by Kajon et al. [32]. Last, this is the first report of detection of HAdV-C57 in respiratory samples collected from pediatric patients with ALRTIs and the first of co-detection of HAdV-C57 with HAdVC-2. HAdV-C57 (formerly designated strain 16700) was first isolated from the feces of a healthy child as part of an acute flaccid paralysis surveillance program. Computational genomic and bioinformatic analysis showed HAdV-C57 to be a recombinant virus with fiber gene nearly identical to HAdV-C6 and a unique hexon distinct from all viruses in species HAdV-C [34, 35]. Out of the three HAdV-C57-infected cases identified here, one was a previously healthy 9-month-old male who presented with bronchopneumonia and conjunctivitis requiring hospitalization. Because only a small number of HAdV-C57 positive cases were found here and all were co-infected with other respiratory viruses, the pathogenic role of HAdV-C57 in respiratory infections will require further investigation.

HAdV type is traditionally determined by virus isolation and subsequently serum neutralization tests, in which antibodies raised against specific type are used to suppress cytopathic effects in tissue culture assays. By nature of its design, this test can only reveal the dominant type. By applying PCR-based identification targeting hexon or fiber genes, co-infections with multiple HAdV types (types from same or different species) have been reported in both immunocompromised and immunocompetent patients [28, 29, 36‐38]. In current study, results showed that one specimen contained both HAdV-C2 and HAdV-C57 by cloned sequencing the PCR products. These were amplified directly from respiratory samples using universal primers of hexon gene. This co-infected phenomenon was confirmed using the fiber gene sequencing results with type-specific primers (data not shown). The specimen was collected from a previously healthy 2.7-year old boy, presenting with fever, coughing and seizure at emergency department on December 10, 2009. Co-infection of different HAdV types has never been reported in any previous studies of Mainland China. The clinical implications of such co-infection remain unclear, and its role in HAdV pathogenesis and evolution will require further study.

Consistent with the report from Guangzhou, Southern China [24], results here showed that 69.6% of HAdV-infected participants were co-infected with one or more other respiratory tract viruses and that RSV was the most frequently co-detected virus. However, no significant differences in clinical characteristics and laboratory findings were found between patients with single HAdV infection and those co-infected with RSV except that co-infections were more frequently observed in younger children. Similarly, a study from Peru also did found no higher prevalence of any clinical manifestations in co-infected patients than in those infected with HAdV alone [26]. The results of another report from Chile showed the clinical severity to be the same in patients with single HAdV infection and those with mixed RSV-HAdV infections [39]. These data demonstrate that, as more sensitive molecular methods become more frequently used to identify pathogens, co-detection of different viruses in the same specimen may also become more common. However, the clinical role of such co-infections will still require independent investigations.

Both HAdV-B7 and HAdV-B3 may cause severe or even fatal pneumonia in even immunocompetent children. Several previous studies showed that patients infected with HAdV-B7 tend to have higher case-fatality rates than those with HAdV-B3 [40, 41]. Two fatal cases were recorded during the study period, and both of these patients were infected with HAdV-B7 alone. Analysis revealed that patients with HAdV-B7 infection had longer duration of fever and higher serum levels of muscle enzymes than HAdV-B3-infected patients. Patients with HAdV-B7 infection also tended to require longer hospital stays although no significant difference was found. These differences have excluded the possible interference by any other co-infected respiratory viruses since this work only evaluated the patients with HAdV infection alone. Such results may suggest that HAdV-B7 infection tended to cause more extrapulmonary tissue damage (such as liver and heart) and may have more severe clinical consequence.

This is a cross-sectional study. Only one respiratory sample was collected from each patient and no viral load analysis was performed. Although HAdV is a pathogen that for long has been known to cause respiratory tract infection, asymptomatic carriage of the virus may persist for weeks [18]. The detection of HAdV in nasopharyngeal aspirate or throat swab with the use of a PCR assay could represent convalescent-phase shedding, so detection may not suggest the current infection.