title: Comparative Burden of Influenza A/H1N1, A/H3N2 and B Infections in Children Treated as Outpatients.
abstract: BACKGROUND
  Few studies have directly compared the clinical impact of different types and subtypes of influenza viruses in children.
  
  
  METHODS
  In a prospective study of respiratory infections in preenrolled cohorts of children ≤13 years of age, we compared the clinical features and the overall burden of illness between outpatient children with A/H1N1, A/H3N2 and B infections. The data were derived from structured medical records filled out by study physicians and from daily symptom diaries filled out by the parents throughout the follow-up period.
  
  
  RESULTS
  Of 358 children included in the analyses, 203 (57%) had influenza A/H1N1, 96 (27%) had A/H3N2, and 59 (16%) had influenza B infection. Children with influenza A/H3N2 were significantly younger (median, 3.2 years) than those with A/H1N1 (median, 4.8 years) or B (median, 5.1 years) infections (P < 0.0001). When adjusted for age, children 3-6 years of age with A/H3N2 infection had a higher frequency of fever ≥39.0°C (67% vs. 38%; P = 0.002), longer duration of fever (median, 4 vs. 3 days; P = 0.02) and more antibiotic treatments (43% vs. 20%; P = 0.004) than did children with A/H1N1 infections. Overall, the clinical presentation, duration of illness, frequency of complications, children's absenteeism from day care or school and parental work absenteeism were comparable between children with A/H1N1, A/H3N2 and B infections.
  
  
  CONCLUSIONS
  Adjusted for age, the clinical manifestations and the burden of illness are largely comparable between children with influenza A/H1N1, A/H3N2 and B infections.
authors.affiliation: From the *Department of Pediatrics, Turku University Hospital, Turku, Finland; †Department of Pediatrics, University of Turku, Turku, Finland; ‡Division of Microbiology and Genetics, Department of Clinical Virology, Turku University Hospital, Turku, Finland; and §Department of Virology, University of Turku, Turku, Finland.
authors.forename: Heli
authors.initials: H
authors.lastname: Silvennoinen
authors.forename: Teemu
authors.initials: T
authors.lastname: Huusko
authors.forename: Tytti
authors.initials: T
authors.lastname: Vuorinen
authors.forename: Terho
authors.initials: T
authors.lastname: Heikkinen
mesh_terms: D000041:Absenteeism; D000293:Adolescent; D000998:Antiviral Agents / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D009980:Influenza A virus; D009981:Influenza B virus; D007251:Influenza, Human / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology* / Q000821:virology*; D008297:Male; D010045:Outpatients / Q000706:statistics & numerical data*; D011446:Prospective Studies
chemical_list: D000998:Antiviral Agents