Epidemiological Transition

The term 'epidemiologic(al) transition' was coined by Abdel Omran in 1971 to refer to the shift from an infectious disease dominated cause of death pattern to one in which chronic degenerative ailments predominate. As such, the epidemiological transition is one strand of a broader process of 'demographic transition' comprising declining birth and death rates, population ageing, changing morbidity patterns, increasing spatial mobility, rising urbanisation, evolving labour force structure and the like. The basic propositions, successive stages, models of transition and claimed determinants of disease promulgated by Omran are outlined first. Critiques and extensions of the theory are then addressed. The impression of smooth, uninterrupted progression through the transition conveyed by Omran is shown to be false and the continuation of epidemiological evolution beyond what was initially envisaged illustrated. Attention in turn is drawn to the tendency to underestimate the continuing burden of infectious disease mortality in present-day developed nations and the debate over the historic importance of different disease determinants. The widening out of the original transition theory into a more encompassing 'health transition' perspective combining both the mortality and morbidity sides of human health is outlined and the 'compression' versus 'expansion' of morbidity debate about the quality of health over the years of additional life expectancy introduced. The importance of recognizing subnational variations in epidemiological profiles is argued and the particular difficulties posed by 'epidemiological polarisation' in many less developed countries noted. Finally the utility of epidemiological transition theory for health planning and strategies is considered.