Human metapneumovirus infection in young children hospitalized with respiratory tract disease

Background: Human metapneumovirus (hMPV) is a newly recognized pathogen associated with respiratory tract disease (RTD). Objectives: To evaluate the incidence of hMPV infection in children hospitalized with RTD and to analyze the virologic and clinical features of hMPV infection. Study Design: All children younger than 5 years of age hospitalized for RTD were included in this 1-year prospective study. hMPV was detected in nasopharyngeal secretions by reverse transcription polymerase chain reaction. The hMPV F gene amplification products were sequenced, and a phylogenetic tree was constructed. Samples were also tested for other respiratory viruses by both direct immunofluorescence assay and virus culture. Results: hMPV, detected in 50 of 589 (8.5%) children, represented the second leading cause of RTD after respiratory syncytial virus (RSV). Infections with hMPV occurred mainly between December and April. hMPV isolates clustered into the 4 subgroups (A1, A2, B1 and B2) currently recognized; the majority (72%) of hMPV isolates belonged to subgroup A1. Among the 35 children infected with hMPV alone, 23 (65.7%) had bronchiolitis, 5 (14.3%) had pneumonia, 2 (5.7%) had asthma exacerbation and 5 (14.3%) had a limited upper RTD. Fifteen (30%) of the hMPV-infected children were coinfected with RSV. As compared with children infected with hMPV or RSV alone, duration of hospitalization and requirement for supplemental oxygen were increased in the hMPV/RSV-coinfected children. Conclusions: hMPV is a frequent cause of RTD in young children. hMPV/RSV coinfection is frequent and could be more severe than a single hMPV or RSV infection.