Family Size, Infections, and Asthma Prevalence in New Zealand Children

Abstract

We conducted a prevalence case-control study to investigate the relation between family composition, infection, and development of asthma at age 7–9 years. Potential cases (399) and controls (398) were selected from the Wellington, NZ, arm of the International Study of Asthma and Allergies in Childhood, a population-based prevalence study. Further screening questions restricted cases to children with a diagnosis of asthma and current medication use (N = 233) and restricted controls to children without a history of wheezing and no diagnosis of asthma (N = 241). After controlling for confounders (including infections, atopy, and socioeconomic status), family size was strongly related to asthma. Having no siblings [prevalence odds ratio (POR) = 2.51; 95% confidence interval (CI) = 1.05–6.01] or one sibling (POR = 1.86; 95% CI = 1.14–3.03) was associated with an increased risk of asthma compared with having more than one sibling. Parent-reported rubeola infection (and possibly other similar viral exanthems) was independently associated with a decreased risk of asthma (POR = 0.48; 95% CI = 0.27–0.83), but reported pertussis infection (POR = 1.57; 95% CI = 0.58–4.24) and day care attendance in the first year of life (POR = 1.81; 95% CI = 0.93–3.51) were not strongly associated with increased risks of asthma. (Epidemiology 1999;10:699–705)