OBJECTIVETo obtain isolated human metapneumovirus (HMPV) strains from clinical specimens collected from infants and children in Beijing and to promote the investigation on this important respiratory pathogen.

METHODClinical specimens including throat swabs from outpatients and nasopharyngeal aspirates from hospitalized children were collected from infants and children visited the affiliated children's hospital for acute respiratory infections during May 2008 to April 2009. HMPV positive specimens identified by RT-PCR and/or direct immunofluorescent assay with monoclonal antibody against HMPV were inoculated to LLC-MK(2) cells and incubated at 37°C and 33°C, respectively. The replication of the virus in the cells was detected by direct immunofluorescent assay followed by RT-PCR. The genotypes of the isolated virus strains were identified by RT-PCR.

RESULTOut of 1092 clinical specimens, 81 were HMPV positive by RT-PCR, the positive rate was 7.4% (81/1092). Among these positive specimens, 33 were inoculated to LLC-MK(2) cells and the replication of HMPV was revealed by antigen detection and RT-PCR from 5 out of these 33 inoculates. These isolated viruses could be passed in LLC-MK(2) cells and were not cross-reacted with other common respiratory viruses, such as ADV, RSV and Parainfluenza viruses 1/2/3 by monoclonal antibodies against these viruses in direct immunofluorescent assay. The HMPV was more likely to be isolated from fresh specimens within 24 hours after the collection of specimens which were not frozen. Four of the 5 isolated strains were identified as genotype A and 1 as genotype B. Unlike other respiratory viruses, these isolated HMPV did not show specific CPE in cell culture and the replication of the virus was identified by antigen detection and RT-PCR.

CONCLUSIONHMPV of both genotypes were isolated from infants and children with acute respiratory infections in Beijing which will accelerate the investigation of this important virus.