Study On Infection Of Human Metapneumovirus In Hospitalized Children With Acute Respiratory Tract Infection

Human metapneumovirus (hMPV), a novel respiratory virus, has recently been recognized as an etiologic agent of respiratory tract infections in children. hMPV has been reported from mostly countries of the world since it was found. It is necessarily that investigate the prevalence and clinical characteristics of hMPV.Four principal methods are used for the diagnosis of respiratory virus infections: virus isolation by culture, antigen detection, RNA or DNA detection, and serological study. In previous studies, virus isolation by culture, reverse transcription-PCR (RT-PCR), and serological study have been used for the diagnosis of hMPV infections. Virus isolation by culture has not found optimal cells of hMPV. Serological study is retrospectively important for differentiation between primary infection and reinfection with hMPV. However, the immunoglobulin G (IgG) and IgM antibody responses to hMPV in the acute phase are not useful for the diagnosis of hMPV infections. Therefore, RT-PCR is concluded to be the most sensitive and specific procedure. However, RT-PCR can be performed only in special laboratories, and it takes more than 6 h to obtain results.Two rapid antigen detection methods are available: an immunofluorescent -antibody test and an enzyme-linked immunosorbent assay (ELISA). The ELISA method with mouse polyclonal antibodies to hMPV has been reported to enable detection of hMPV antigens of hMPV-infected cells in culture. However, there has been no study on the detection of hMPV antigens in clinical samples. The immunofluorescent-antibody test of respiratory epithelial cells has been shown to be a very useful method to detect other respiratory viruses, such as hRSV, parainfluenza virus, adenovirus, and influenza virus.ObjectiveTo elucidate the prevalence and clinical characteristics of human metapneumovirus (hMPV) in hospitalized children with acute respiratory tract infection by IFA.MethodsFrom Nov 2006 to Feb 2007 we collected nasopharyngeal swab samples from 112 children who were admitted to Xijing Hospital in Xi'an, China, due to respiratory symptoms. The nasopharyngeal swabs were placed in 1.3 ml of virus transport medium for IFA. The samples were collected within 7 days after the onset of illness, after the possibility of infection with hRSV or influenza A or B virus was excluded by a rapid antigen detection test. Respiratory tract swab were collected from all patients within 48 hours after admission. The specimens were routinely tested for respiratory syncytial virus, Influenza virus A and B, parainfluenza virus 1 to 3 and adenovirus by direct fluorescent assay(DFA).The 65 specimens negative by DFA were tested for hMPV by IFA.Results1. We confirmed that there were at least more than 100 epithelial cells on one spot at×400 magnification under a fluorescent microscope. Typical IFA -positive and IFA-negative staining patterns of nasopharyngeal epithelial cells are shown in Fig.2. The presence of at least one cell with a specific staining pattern was defined as a positive result.3. hMPV was identified in 8(12.31%) of the 65 specimens tested. hMPV infection accounted for 7.14% of the infections in the 112 children under study.4. hMPV was mostly identified in Nov and Jan.5. There was no significant difference between age groups in terms of the prevalence of hMPV (P > 0.05).6. The clinical symptoms of hMPV infection can not be discriminated from the infection of other common respiratory viruses.Conclusion1. We applied IFA to the detection of hMPV antigens in nasopharyngeal secretions for the rapid diagnosis of hMPV infection. The present study showed that IFA with an anti-hMPV mouse monoclonal antibody could detect hMPV antigens in nasopharyngeal secretions.2. The acute respiratory-tract infections among children of Xi'an city are associated with hMPV infection. hMPV was identified in 8(12.31%) of the 65 specimens tested. It is indicated that hMPV is also an important pathogen in our country.3. Differences of the infection rate may be associated with research period, study population and region. Moreover, present investigations may underestimate its infection rate because the specimens were routinely tested for respiratory syncytial virus, Influenza virus A and B, parainfluenza virus 1 to 3 and adenovirus by direct fluorescent assay(DFA) and negative specimens were tested for hMPV.4. The individuals aged from 6months to 6years old have been exposed to hMPV, and by age of 5 years, over 75% of children in our study have been infected. Differences of the age distribution may be associated with internalizal standard of investigative objects.5. Studies of the seasonal distribution have shown that this virus is prevalent mainly during the winter-spring period. hMPV was mostly identified in Nov and Jan in our study.6. Clinical symptoms range from fever, cough, rhinorrhea and influenza-like symptoms to severe lower respiratorytract infection, bronchitis, bronchiolitis and pneumonia.