Has the prevalence of asthma increased in children? Evidence from the national study of health and growth 1973-86

Abstract

Objectives - To estimate changes in the prevalence of reported symptoms of respiratory disease and reported diagnoses of asthma and bronchitis in primary school children in England between 1973 and 1986. Design - Mixed longitudinal survey. Setting - Representative sample of English primary schools in 22 areas. Participants - 15000 Boys and 14156 girls each studied at least once between 1973 and 1986. Data collected - Whether, according to the parent or guardian, the child had wheezed, wheezed on most days or nights, or had attacks of bronchitis or asthma in the past year. Results - Within age groups trends in successive annual cohorts showed an increasing prevalence of asthma for each annual birth cohort (boys, 6.9%, p < 0.001; girls, 12.8%, p < 0.001) and of wheeze on most days or nights (boys, 4.3% per cohort, p < 0.001; girls, 6.1% per cohort, p < 0.001) and a falling prevalence of bronchitis (boys, -4.7% per cohort, p < 0.001; girls, -5.8% per cohort, p < 0.001). There was a smaller increase in the prevalence of wheeze whether or not it occurred on most days or nights, and this increase was significant only among the girls (boys, 1.0% per cohort, p > 0.05; girls, 1.7% per cohort, p < 0.05). Although the rate of increase of 'asthma' was greater than the rate of decrease in 'bronchitis', the baseline prevalence of asthma was much lower than that of bronchitis, and the total proportion of children with either diagnosis declined slightly over the whole period. The main change was an increase in the proportion of children whose parents stated that they had persistent wheeze and yet did not have a report of either 'asthma' or 'bronchitis'. Conclusions - These results suggest that there has been a true increase in morbidity that is not simply due to changes in diagnostic fashion. The increase is large enough to explain much if not all of the increase in admission to hospital and mortality, and it underlines the importance of an understanding of the aetiology of asthma in tackling the causes of the recent increase.