title: Viral etiologies of infant bronchiolitis, croup and upper respiratory illness during 4 consecutive years.
abstract: BACKGROUND
  Prospective data on viral etiology and clinical characteristics of bronchiolitis and upper respiratory illness (URI) in infants are limited.
  
  
  METHODS
  This prospective cohort enrolled previously healthy term infants during inpatient or outpatient visits for acute URI or bronchiolitis during September to May 2004 to 2008. Illness severity was determined using an ordinal bronchiolitis severity score. Common respiratory viruses were identified by real-time reverse-transcriptase polymerase chain reaction.
  
  
  RESULTS
  Of 648 infants, 67% were enrolled during inpatient visits and 33% during outpatient visits. Seventy percent had bronchiolitis, 3% croup and 27% URI. Among infants with bronchiolitis, 76% had respiratory syncytial virus (RSV), 18% human rhinovirus (HRV), 10% influenza, 2% coronavirus, 3% human metapneumovirus and 1% parainfluenza virus. Among infants with croup, 39% had HRV, 28% parainfluenza virus, 28% RSV, 11% influenza, 6% coronavirus and none human metapneumovirus. Among infants with URI, 46% had HRV, 14% RSV, 12% influenza, 7% coronavirus, 6% parainfluenza virus and 4% human metapneumovirus. Individual viruses exhibited distinct seasonal, demographic and clinical expression.
  
  
  CONCLUSIONS
  The most common infections among infants seeking care in unscheduled medical visits for URI or bronchiolitis were RSV and HRV. Demographic differences were observed between patients with different viruses, suggesting that host and viral factors play a role in phenotypic expression of viral illness.
authors.affiliation: From the Departments of *Pediatrics, †Biostatistics, ‡Medicine, and §Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN.
authors.forename: E Kathryn
authors.initials: EK
authors.lastname: Miller
authors.forename: Tebeb
authors.initials: T
authors.lastname: Gebretsadik
authors.forename: Kecia N
authors.initials: KN
authors.lastname: Carroll
authors.forename: William D
authors.initials: WD
authors.lastname: Dupont
authors.forename: Yassir A
authors.initials: YA
authors.lastname: Mohamed
authors.forename: Laura-Lee
authors.initials: LL
authors.lastname: Morin
authors.forename: Luke
authors.initials: L
authors.lastname: Heil
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Minton
authors.forename: Kimberly
authors.initials: K
authors.lastname: Woodward
authors.forename: Zhouwen
authors.initials: Z
authors.lastname: Liu
authors.forename: Tina V
authors.initials: TV
authors.lastname: Hartert
authors.forename: John V
authors.initials: JV
authors.lastname: Williams
mesh_terms: D000328:Adult; D001988:Bronchiolitis / Q000453:epidemiology* / Q000473:pathology / Q000821:virology*; D015331:Cohort Studies; D003440:Croup / Q000453:epidemiology* / Q000473:pathology / Q000821:virology*; D003710:Demography; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D011446:Prospective Studies; D060888:Real-Time Polymerase Chain Reaction; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000473:pathology / Q000821:virology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012720:Severity of Illness Index; D014780:Viruses / Q000145:classification / Q000302:isolation & purification*