Human metapneumovirus infection in young children hospitalized with acute respiratory tract disease - Virologic and clinical features

Background: Human metapneumovirus (hMPV) is an emerging virus associated with acute respiratory tract infections (ARIs) in young children. Objectives: To evaluate virologic and clinical features of hMPV infection during 2 consecutive winter-spring seasons. Methods: Nasal washes were obtained from children younger than 5 years of age hospitalized for ARI. Specimens were tested for hMPV by reverse transcription-polymerase chain reaction. The hMPV F gene amplification products were sequenced, and phylogenetic trees were constructed. Results: A high incidence of hMPV infection (25.3%) was observed during the 2005-2006 winter-spring season, whereas a much lower rate of infection (4.7%) during the following season was found. Phylogenetic analysis revealed that, during the 2 seasons, 60.4% of the hMPV detected were A2a, 22.9% were A2b, 4.2% were B1, and 12.5% were B2. hMPV A1 strains were not detected in any tested specimen. Clinical diagnosis was bronchiolitis in 57.1%; pneumonia in 25%; and a upper respiratory tract illness in 17.8%. Bronchiolitis was more frequent in children less than 1 year of age (80%) than in children more than 1 year of age (30.8%) (P < 0.05). When hMPV was found frequently, the hMPV spread overlapped with that of respiratory syncytial virus (RSV) and hMPV/RSV coinfections were common events (19 of 39; 48.7%). hMPV/RSV-coinfected children developed pneumonia more frequently than hMPV-infected patients (57.9% versus 20%) but no differences in disease severity (gauged by duration of hospitalization and requirement of oxygen) were observed. Conclusions: These results provide further evidence of the importance of hMPV as a pathogen associated with ARI in young children. Involvement of hMPV/RSV coinfection in cases of pneumonia is suspected.