The effects of poverty and ageing on the increase in tuberculosis

Among the causes of the current increase in tuberculosis worldwide are poverty and ageing. It has been widely accepted that tuberculosis and poverty have been closely linked since the scientific study of the disease began. The decline of tuberculosis in developed countries before the arrival of specific chemotherapy was largely attributed to improvement in social conditions. With the rapidly increasing world population and the wider disparity of income, more and more people are falling into poverty, whichever way it is defined. Studies in the developed world show that the close association between tuberculosis and poverty remains. Some workers in the field even suggest that tuberculosis cannot be controlled until the issue of global poverty has been addressed. This may be too pessimistic. It may be possible to define accurately which aspects of poverty are most closely associated with tuberculosis and to deal with those specifically. Within developed countries longevity is increasing. The population now in their seventies, or older, even in developed countries, will have been alive when the disease was highly prevalent in the communities in which they lived. The majority will, therefore, have acquired infection, and in a substantial minority of these infection may reactivate to cause disease as the ageing process weakens host immunity. In the indigenous Caucasian population of Western Europe, rates of disease are highest in elderly males. Previous research showed that beyond the age of forty, the incidence of disease declined with increasing age. The higher rates in the elderly were a result of the residue of higher rates from birth cohorts born earlier. Data presented in this article suggest that this pattern may be altering such that the incidence of disease actually increases after a certain age is reached. This could have important repercussions for disease incidence in the emerging economies of the Pacific Rim, where longevity is increasing most rapidly.