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Epidemiological Transition Model
Introduction
A fundamental change in the most frequently recorded causes of death, longer life expectancy and an increasing proportion of older people in the population have been characteristic features of the epidemiological transition in Western countries. Interest in the transition model has renewed recently with more cause-specific mortality data becoming available from low- and middle-income countries (LMICs) [1-3]. Integration with the socio-ecological model in epidemiology has been suggested to provide a comprehensive framework for investigating and understanding changing patterns of health and disease [4, 5]. Omran's original paper on 'epidemiologic transition' in 1971 drew attention to profound changes in the cause of death structure, and identified different stages and models of transition [6]. It diverged from the demographic transition model of mortality, fertility and population change by focusing on a shift from one predominant group of diseases, infectious diseases, to 'degenerative and man-made diseases' considered to be distinctly different. More recently, the term 'non-communicable disease' has been widely used for conditions traditionally regarded as having no infectious causes, and 'chronic disease' for those with long duration (usually at least 3 months). However, infectious causes have been confirmed for a significant number of these in recent decades (e.g. gastric cancer, cervical cancer, peptic ulcer), indicating a fundamental weakness in the concept of transition. The false dichotomy on which the original transition model was based reflects the lack of knowledge at the time about the pathogenesis and aetiology of chronic diseases. In contrast, external manifestations and transmission patterns were conspicuous for most acute infectious diseases, single microbial causal agents had been identified and effective methods of control were well established [7].
Infectious diseases are caused by specific pathogenic microorganisms or parasites that are necessary for them to occur and be transmitted. They include those in the International Classification of Diseases (ICD) chapter, 'certain infectious and parasitic diseases', some 'diseases of the respiratory system' (e.g. influenza, pneumonia) and a few local infections classified elsewhere (e.g. urinary tract infections) [8]. Certain infectious diseases can persist beyond a short-term acute phase into an active chronic phase, become inactive but potentially active or cause some other morbid condition. Infectious diseases have now been superseded by other acute and chronic conditions as the most frequently...