The epidemiology of asthma

Epidemiology is the study of populations to discover modifiable factors that contribute to disease incidence with a view to reducing disease burden through prevention. Asthma is a complex, polygenic disease with heterogeneous manifestations making it difficult to define precisely in epidemiologic studies. Despite this, global efforts to harmonise outcome definitions have led to detailed understanding of the temporal and spatial variations of asthma prevalence in children. Asthma prevalence notably increased markedly in several high-income countries during the final three decades of the 20th Century but the cause for this has never been fully established.

Early life has been implicated as a critical period for the development of asthma. Many environmental influences have been considered as potential risk factors for asthma but few have been associated with more than modest increases in risk. One barrier to identifying causal risk factors is the clustering of environmental factors with consequent confounding of relationships between environment and disease. Thus, even strong and reproducible associations can seldom be regarded as causal without experimental evidence, which is currently lacking.

Despite these difficulties, New approaches to asthma classification, meticulous observations in birth cohorts, technological advances that enable assessment of genetic risk and identification of biomarkers of disease pathways, and analytical advances, have led to real advances in understanding asthma pathogenesis. The interaction of allergic sensitization with viral respiratory infections offers a promising target for the development of preventative interventions in asthma.