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.