OBJECTIVETo isolate and characterize the newly discovered human metapneumovirus (hMPV) in Chongqing, China and elucidate the clinical manifestations of hMPV infection.

METHODSEighty-six patients hospitalized for acute respiratory tract infection in Children's Hospital, Chongqing University of Medical Sciences from December 2004 to July 2005 were enrolled in the present study. Nasopharyngeal aspirates were collected for screening for common respiratory viruses by direct immunofluorescence assay, including respiratory syncytial virus, influenza virus types A and B, parainfluenza virus types 1, 2, 3 and adenovirus, and for inoculating onto Vero-E6 and LLC-MK2 cells for hMPV isolation. Cultures were maintained in the presence of trypsin and observed for development of cytopathic effect (CPE) for 3 weeks. Presence of hMPV was first indicated by positive CPE and subsequently confirmed by reverse transcription polymerase chain reaction targeting N and F genes. Sequence of amplified F fragments were analyzed and submitted to NCBI GenBank. The clinical findings of hMPV infection were collected and analyzed.

RESULTSOf the collected 86 NPAs, six showed CPE characterized by clustering of infected cells, increased granules and eventuall detachment from cell monolayer and obvious syncytium formation. Successful isolation of hMPVs was confirmed with RT-PCR targeting hMPV F and N genes. Of the six hMPV-positive specimens, two were collected in winter (December, January), two in spring (May) and the other two in autumn (June, July). All the six patients were younger than 2 years of age with disease spectrum of bronchiolitis (2/6), bronchopneumonia (2/6), infantile asthma (1/6) and upper respiratory tract infection (1/6). Clinical findings included fever, cough, wheezing, polypnea, cyanosis and rales. Parainfluenza 3 and adenovirus seemed to beviral pathogens of co-infection.

CONCLUSIONSix hMPVs were successfully isolated in the mainland of China for the first time. HMPV appears to be one important viral pathogen for acute lower respiratory tract infections in young children with a detection rate of 7% (6/86) by viral isolation. The virus causes respiratory diseases similar to those caused by respiratory syncytial virus. These findings highlight the need for future investigations to define disease burden of hMPV infection and molecular epidemiology among children in China.