title: Incidence of influenza-related hospitalizations in different age groups of children in Finland: a 16-year study.
abstract: BACKGROUND
  children are frequently hospitalized with inﬂuenza-associated illnesses. Few virologically conﬁrmed population-based studies of pediatric hospitalizations performed during several consecutive seasons are vailable.
  
  
  METHODS
  this 16-year retrospective study consisted of all children ≤ 16 years of age who were treated for virologically conﬁrmed inﬂuenza at the Department of Pediatrics, Turku University Hospital, Finland, between July 1, 1988 and June 30, 2004. Calculation of the population-based rates of hospitalization in different age cohorts was based on children (n = 69,068) who lived within the 38 municipalities whose acute pediatric care was provided solely by Turku University Hospital.
  
  
  RESULTS
  during the study period, 401 children were hospitalized with virologically conﬁrmed inﬂuenza. The average annual incidences of inﬂuenza-related hospitalizations were highest among children <6 months (276 [95% conﬁdence interval, 220–336] per 100,000) and 6 to 11 months (173 [95% conﬁdence interval, 129–220] per 100,000) of age. For both inﬂuenza A and B, the rates of hospitalization were highest among children younger than 1 year of age. Inﬂuenza A accounted for 82% and inﬂuenza B for 18% of all hospitalizations. A total of 40 (10.0%) children received treatment at the intensive care unit. Of all 401 children with conﬁrmed inﬂuenza infection, only 216 (53.9%) had a discharge International Classiﬁcation of Diseases code related to inﬂuenza.
  
  
  CONCLUSIONS
  the high incidence of inﬂuenza-associated hospitalization among infants less than 6 months of age underscores the need to ﬁnd effective ways to prevent inﬂuenza in this age group, in which inﬂuenza vaccines are not currently licensed for use.
authors.affiliation: Department of Pediatrics, Turku University Hospital, Turku, Finland.
authors.forename: Heli
authors.initials: H
authors.lastname: Silvennoinen
authors.forename: Ville
authors.initials: V
authors.lastname: Peltola
authors.forename: Raija
authors.initials: R
authors.lastname: Vainionpää
authors.forename: Olli
authors.initials: O
authors.lastname: Ruuskanen
authors.forename: Terho
authors.initials: T
authors.lastname: Heikkinen
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D005260:Female; D005387:Finland / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology; D008297:Male; D012189:Retrospective Studies