Population health in transition.

Abstract

Until recent times most deaths were caused by infectious diseases, degenerative diseases, or violence. Let us ignore violent deaths, as they can occur at any age. Infectious diseases are a threat from the day of birth and, indeed, the very young are most susceptible to their attack. People die of degenerative diseases at older ages because it usually takes time for the body to degenerate and there is little else to die from, though they must eventually die of something. What happened in the mortality transition was the conquest of infectious disease, not a mysterious displacement of infection by degeneration as the cause of death. The resulting demographic transition with its changing age of death and the existence of large numbers of people afflicted with chronic degenerative disease (rather than life-threatening infectious disease) is important for planning health services and medical training, which is the current focus of the burden of disease approach. Why did Abdel Omran's essay (1) have such an impact on the public health community, an impact with echoes of Malthus's views on population? There are certain similarities to The First Essay of Malthus in 1798: Omran firmly stated a number of propositions, which were only sparingly spelled out and buttressed by limited references. Also, he republished the paper several times although, unlike Malthus, his additions were largely limited to applying the thesis to the United States and suggesting a fourth stage (2). Omran postulated the displacement of pandemics by "degenerative and man-made diseases" without explaining what was meant by the latter, but in 1982 he specified that it included "radiation injury mental illness, drug dependency, traffic accidents, occupational hazards" (2). The public health community was undoubtedly attracted by the prospect of combating man-made diseases: what human activity could create, human activity could correct. The other attraction was the suggestion that somehow degenerative and man-made diseases had replaced infectious ones, which presented, a picture of combat between warring camps of disease into which the health professionals could throw themselves. Omran did in places relate this replacement to mortality decline and changing age structures, though he touched upon age structure only very lightly and usually treated a population as an undifferentiated unit. This approach was central in giving the paper such force. Omran added strength to his argument by segmenting the epidemiological transition into periods with different mortality patterns and disease levels. Thomas McKeown also did this, though only his first two historical papers (3, 4) were published before Omran's. The other form of segmentation Omran used was numbered propositions, to which we now turn. Proposition One, "that mortality is a fundamental factor in population dynamics", has always been agreed: in all demographic transition theories it is the prior decline in mortality that in due course precipitates the fertility decline. It is true that for decades after the Second World War demographers gave more attention to the causes and nature of the fertility decline than to those of the mortality decline, though they stressed that such attention was necessary because of the preceding unforeseen steep mortality decline in developing countries. The importance of Omran's and McKeown's work is that they drew attention to this imbalance. The core of Proposition Two, "During the transition, a long-term shift occurs in mortality and disease patterns" is clear, but the subsequent excursion into the determinants of the transition is subject to the same criticisms as have been levelled at McKeown's work. The ascription of the 19th-century Western mortality decline primarily to ecobiological and socioeconomic factors (McKeown said nutrition), the argument that "the influence of medical factors was largely inadvertent", and the implication that the struggle against infectious disease was unimportant after the turn of the century, are all contestable. …