OBJECTIVEThe fact that the acute lower respiratory infections (ALRI) are associated with a newly discovered virus, human metapneumovirus (hMPV), has been shown in several studies. The authors conducted this study to understand the etiological and clinical characteristics of bronchiolitis, one of the most common ALRI in infants, caused by hMPV.

METHODSNasopharyngeal aspirate specimens from 54 out of 126 infants with bronchiolitis admitted to the Children's Hospital Affiliated to Capital Institute of Pediatrics, Beijing from November 2002 to February 2003 were examined for hMPV gene fragments by reverse transcription-polymerase chain reaction (RT-PCR). Prior to the detection, the specimens were confirmed as negative for the common respiratory pathogens including RSV, influenza A and B, parainfluenza I, II, III, adenovirus, Mycoplasma pneumoniae by indirect immunofluorescence test, virus isolation and ELISA test. The clinical data of the patients diagnosed etiologically as hMPV infection analyzed included the infants' age, sex, the degree of fever, the severity of wheezing and clinical Lowell score, the findings of chest examination and chest X-ray, the white blood cell count and blood gas analysis, the course of the disease, the major treatments and the outcome of the disease.

RESULTSTwenty-one specimens showed the predicted 213 bp PCR products in agarose gel and the positive rate was 16.7% of all patients (21/126) and 39% of the patients with negative results for common respiratory pathogens detections (21/54). The range of patients' age was 2 - 15 months and the young infants with hMPV bronchiolitis (1 - 6 month of age) accounted for 62% and the male:female ratio was 3.2:1. The patients presented a low-medium grade fever (T < 39 degrees C) accounted for 86%; 81.0% of patients had a white blood cell count lower than 10.0 x 10(9)/L. The radiological findings were patchey opacity in both lungs (68%) and(or) hyperinflation (62%). Assessed by the Lowell score system, 5 out of 21 cases were considered as severe cases. The major clinical findings of hMPV bronchiolitis had no significant difference compared with that of subgroup A hRSV bronchiolitis, and showed longer course of disease than that of subgroup B hRSV bronchiolitis (P < 0.01).

CONCLUSIONSOf the infants with bronchiolitis hospitalized in our hospital from November of 2002 through February of 2003, 16.7% were caused by hMPV infection. These data showed that the major clinical characteristics and the outcome of treatment of hMPV bronchiolitis had no statistically significant difference compared to the cases with either subgroup A or subgroup B hRSV infection.