OBJECTIVEAdenovirus (ADV) is one of the most common causes of acute respiratory infections in infants and children. The objective of this study was to investigate the prevalence of adenovirus infection among pediatric patients with acute respiratory infections in Beijing and the types of the adenoviruses circulating in Beijing on the molecular bases.

METHODClinical specimens including throat swabs from outpatients and nasopharyngeal aspirates from hospitalized patients were collected from patients with acute respiratory infections in a consecutive period of 6 years from Jan 2003 to Dec 2008. Adenoviruses were identified from the collected clinical specimens by tissue culture and/or immunofluorescence assay and typed by nested-PCR based on the sequence of the encoding gene of hexon. Primers were designed for PCR amplification using hexon gene of adenovirus as target. One primer pair was designed as universal primers for amplifying a 1278 bp gene fragment located at the hexon gene of adenovirus types 3, 7, 11 and 21. Four primer pairs with the sequences located within the region of this 1278 bp fragment were designed specifically for amplifying adenoviruses types 3, 7, 11 or 21, respectively, which were used for a multiplex nest-PCR in a single tube. The products from this multiplex nest-PCR were 502 bp (for type 3), 311 bp (for type 7), 880 bp (for type 11) and 237 bp (for type 21), respectively, and the type of the adenovirus tested can be determined after agarose electrophoresis analysis of the PCR products. For those strains which could not be typed by the multiplex nest-PCR, the gene fragment was amplified by a universal primer pair for all adenovirus types from group A to F and the PCR products were sequenced directly.

RESULTOut of 17 941 clinical specimens collected, including 4378 throat swabs from outpatients and 13 563 nasopharyngeal aspirates from hospitalized patients, 304 were adenovirus positive by tissue culture and/or immunofluorescence assay, the overall positive rate was 1.69% (304/179 41). Among these 304 adenovirus positive specimens, 184 were by virus isolation and 184 by immunofluorescence assay, among which 64 were positive by both methods. The types of the adenoviruses were tested for 285 patients including 174 viral isolates and 111 clinical specimens. By using the multiplex nest-PCR, 272 were typable, including 174 (61.1%, 174/285) for ADV3, 92 (32.3%, 92/285) for ADV7, 6 for ADV11 (2.1%, 6/285) and no adenovirus type 21 was detected. Sequence analysis for those 13 nontypable specimens by the multiplex nest-PCR showed that 9 were ADV2 (3.2%, 9/285), 2 were ADV6 (0.7%, 2/285), 1 was ADV1 (0.4%, 1/285) and 1 was ADV5 (0.4%, 1/285). Most of the patients positive for adenovirus were under 5 years of age and 64.4% were from patients with lower respiratory infections, such as bronchiolitis and pneumonia. All the 5 cases of severe pneumonia with pulmonary failure were caused by ADV7 infection.

CONCLUSIONAdenovirus is still an important pathogen for acute respiratory infection in infants and young children and most of the adenoviruses associated with acute respiratory infections in children in Beijing from 2003 to 2008 were ADV3 and ADV7. ADV7 could cause severe lower respiratory infections.