title: Human metapneumovirus infection in young children hospitalized with acute respiratory tract disease: virologic and clinical features.
abstract: BACKGROUND
  Human metapneumovirus (hMPV) is an emerging virus associated with acute respiratory tract infections (ARIs) in young children.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Experimental and Applied Medicine, Section of Microbiology, University of Brescia Medical School, Brescia, Italy.
authors.forename: Sonia
authors.initials: S
authors.lastname: Caracciolo
authors.forename: Chiara
authors.initials: C
authors.lastname: Minini
authors.forename: Domenico
authors.initials: D
authors.lastname: Colombrita
authors.forename: Daniele
authors.initials: D
authors.lastname: Rossi
authors.forename: Nunzia
authors.initials: N
authors.lastname: Miglietti
authors.forename: Emanuela
authors.initials: E
authors.lastname: Vettore
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Caruso
authors.forename: Simona
authors.initials: S
authors.lastname: Fiorentini
mesh_terms: D000367:Age Factors; D001988:Bronchiolitis / Q000821:virology; D002675:Child, Preschool; D015897:Comorbidity; D005260:Female; D005838:Genotype; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D029121:Metapneumovirus / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D009296:Nasal Cavity / Q000821:virology; D017817:Nasal Lavage Fluid; D018184:Paramyxoviridae Infections / Q000453:epidemiology / Q000503:physiopathology / Q000821:virology*; D010802:Phylogeny; D011014:Pneumonia / Q000821:virology; D012367:RNA, Viral / Q000235:genetics; D018357:Respiratory Syncytial Virus Infections / Q000150:complications / Q000453:epidemiology; D012136:Respiratory Syncytial Viruses / Q000302:isolation & purification; D012141:Respiratory Tract Infections / Q000453:epidemiology / Q000503:physiopathology / Q000821:virology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017385:Sequence Homology
chemical_list: D012367:RNA, Viral