An overview of recent trends in asthma epidemiology

Although a number of international studies have suggested that the prevalence of asthma is increasing, it remains unclear whether the trend is due to an increase in the number of incident cases on, an increase in duration of active disease. A large proportion of the measurable increase is probably attributable to enhanced diagnostic awareness and reclassification of other respiratory conditions. Even if these trends represent 'true' increases In disease burden within populations, international studies suggest different rates of change in various population subgroups, particularly among differing age groups. A case study of asthma in the USA demonstrates the difficulty in understanding the aetiology of these changes. This study indicated that the increase in prevalence is limited to age groups under 45 yrs. Amongst children, the increase in prevalence was seen almost entirely in the 5-14 yr age range. Asthma hospitalization rates have remained steady over the past decade, with the exception of significant incresses in children aged under 5 yrs. Asthma mortality decreased for nearly a decade (1970s) followed by a decade of increase (1980s) and is now achieving a steady-state, with rates similar to those of 25 yrs ago. Changes in asthma prevalence, morbidity and mortality are clearly different from each other, and cannot easily be explained by a single or even several unifying theories.