Respiratory disease in young adults: influence of early childhood lower respiratory tract illness, social class, air pollution, and smoking.

The prevalence of cough during the day or night in winter has been studied in 3,899 20-year-olds. These were members of a cohort born in England, Scotland, and Wales in the last week of March 1946. The prevalence of cough and current smoking habits have been related to events recorded during infancy and childhood-that is, exposure to air pollution, social class of father, and lower respiratory tract illness under 2 years of age. At age 20, of these factors cigarette smoking was found to have the greatest effect on symptom prevalence, followed by a history of a lower respiratory tract illness under 2 years of age. Social class and air pollution had little effect.