Risk factors and markers of asthma control differ between asthma subtypes in children

Background There is limited understanding about risk factors for asthma, and few studies have presented an overall picture of factors associated with asthmasubtypes in schoolchildren. The aim of this study was to evaluate risk factors and markers of asthmacontrol associated with asthmasubtypes up to preadolescence. Methods A Swedish birth cohort of 3015 children was followed for 12 yr using repeated parental questionnaires. At 8 yr, clinical investigation was performed, specifically evaluating lung function, allergic sensitization (IgE > 0.35 kUA/l), and body mass index (BMI). Children were categorized into three subtypes: transient asthma– asthmaat 4 and 8, but not at 12 yr (n = 71), late-onset asthma– asthmaat 12 yr, but not earlier (n = 103), and persistent asthma– asthmaat 4, 8 and 12 yr (n = 125). Results At 8 yr of age, high BMI (>85th percentile), sensitization, and rhinitis were significantly associated with late-onset asthma(p < 0.05). Prominent risk factors at birth associated with persistent, but not late-onset asthma, were male sex, tobacco exposure and, heredityfor atopy(p < 0.05). Children with persistent asthmawere also found to have significantly reduced lung function at 8 yr of age, more eczema/rhinitis, and were more atopic than non-asthmatics (p < 0.05). For persistent asthma, symptoms changed from 8 to 12 yr, with fewer nocturnal symptoms, less healthcare utilization, and less frequent wheeze at 12 yr (p < 0.05). Conclusion Risk factors differ between asthmasubtypes and markers of asthmacontrol vary with age up to preadolescence.