title: Clustering of acute respiratory infection hospitalizations in childcare facilities.
abstract: OBJECTIVE
  To estimate how risk of acute respiratory infection (ARI) hospitalization in children attending childcare facilities with a recently (within 1 month) hospitalized child is affected by gender, age and other characteristics.
  
  
  METHODS
  Population-based prospective cohort study of 436 434 Danish 0-5-year-old children attending childcare during 1989-2004. Information was collected from Danish registers. Main outcome measure was incidence rate ratios (IRRs) of in-patient hospitalization for ARI.
  
  
  RESULTS
  During 1 777 999 person-years of follow-up 42 681 hospitalizations for ARI occurred, of which 362 (1%) occurred within 1 month after another child was hospitalized for ARI in the facility. Children attending a facility with a recent ARI hospitalization had an increased risk of 42% (95% CI 27%;60%) compared with other children. The increased risk was higher in 0-2-year-old children than in 3-5-year-old children (55% vs 17%, p = 0.02) and if the latest hospitalized child was 0-2 years rather than 3-5 years (52% vs 19%, p = 0.04). The increased risk was similar in boys and girls, but was higher if the latest hospitalized child was a boy rather than a girl (52% vs 13%, p = 0.02).
  
  
  CONCLUSIONS
  Although occurring infrequently, clustering of ARI hospitalizations involve 0-2-year-olds and boys as first hospitalized child relatively more often than would be expected.
authors.affiliation: Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark. mka@ssi.dk
authors.forename: Mads
authors.initials: M
authors.lastname: Kamper-Jørgensen
authors.forename: Christine Stabell
authors.initials: CS
authors.lastname: Benn
authors.forename: Jacob
authors.initials: J
authors.lastname: Simonsen
authors.forename: Nana
authors.initials: N
authors.lastname: Thrane
authors.forename: Jan
authors.initials: J
authors.lastname: Wohlfahrt
mesh_terms: D000208:Acute Disease; D000367:Age Factors; D000704:Analysis of Variance; D002656:Child Day Care Centers; D002675:Child, Preschool; D016000:Cluster Analysis; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D011446:Prospective Studies; D012042:Registries; D012141:Respiratory Tract Infections / Q000453:epidemiology*; D012307:Risk Factors; D012737:Sex Factors