title: Population-based study of the association between asthma and pneumococcal disease in children.
abstract: BACKGROUND
  Although asthma has recently been established as a risk factor for pneumococcal disease (PD), few studies have specifically evaluated this association in children.
  
  
  METHODS
  We conducted a nation-wide population-based cohort study of the effect of asthma on childhood PD among all singleton live births in Denmark from 1994 to 2007, before the introduction of the 7-valent pneumococcal conjugate vaccine. All data were abstracted from Danish medical registries. Because underlying comorbidity substantially increases the PD risk in children, standard methods were used to assess the evidence of biologic interaction between comorbidity and asthma on the risk of PD.
  
  
  RESULTS
  There were 2,253 cases of childhood PD among 888,655 children born in Denmark from 1994 to 2007. The adjusted incidence rate ratio of the effect of asthma on childhood PD was 2.2 (95% confidence interval [CI]: 2.0, 2.5). Age-stratified incidence rate ratios were 2.1 (95% CI: 1.8, 2.9) in children 6 months to <24 months, 4.1 (95% CI: 3.3, 5.1) in children 24 months to <60 months, and 2.3 (95% CI: 1.6, 3.2) in children ≥60 months. Evaluation of the biologic interaction between asthma and comorbidity in older children revealed that 55% (24 months to <60 months) to 73% (≥60 months) of cases among asthma-exposed children can be accounted for by the interaction between asthma and comorbidity.
  
  
  CONCLUSIONS
  These results confirm that asthma is an important risk factor for PD in children and suggest that children with underlying comorbidities are more sensitive to the effect of asthma on PD than children without comorbidities.
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA ; Department of Pediatrics, Boston University School of Medicine, Boston, MA, USA.
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Shea
authors.affiliation: Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA, USA ; Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Lash
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Sussie
authors.initials: S
authors.lastname: Antonsen
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA ; Boston Collaborative Drug Surveillance Program, Boston University, Boston, MA, USA.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Jick
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA ; Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Henrik T
authors.initials: HT
authors.lastname: Sørensen
keywords: asthma; children; comorbidity; pneumococcal disease