Asthma and bronchitis in Sydney schoolchildren. II. The effect of social factors and smoking on prevalence.

During a study of the prevalence of asthma and bronchitis in Sydney schoolchildren, some social and environmental factors were documented to ascertain if these affected the prevalence of either of these diseases. Socioeconomic status obtained from father's occupation, area of residence, family size, nationality, country of birth and smoking habits were examined. Although small differences were found between groups, no consistent relationship was found between social class and lung disease with the exception of increased prevalence of asthma in boys in social class I and girls in social class II. There were no major associations with area of residence or with family size. Children who were born outside Australia tended to have less asthma and bronchitis than children born inside Australia and migrant children tended to first develop asthma several years after arriving in Australia. Bronchitis was found to be more common in children with an earlier history of bronchitis in infancy and early childhood. The prevalence of recent bronchitis in the group of children who smoked 20 or more cigarettes per week was higher than that in the nonsmoking group of children.