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All humans need protection against the elements, somewhere to store food and prepare meals, and a secure place to raise offspring. The effects of housing conditions on health have been known since antiquity. Deplorable living and sanitary conditions in urban slums became a political issue in the nineteenth century when accounts by journalists, novelists, and social reformers aroused public opinion. Osler's Principles and Practice of Medicine (1892) and Rosenau's Preventive Medicine and Hygiene (1913) noted the association between overcrowding and common serious diseases of the time such as tuberculosis and rheumatic fever. Housing remains a sensitive political issue in many communities, because it is unsatisfactory, insufficient, inadequately served by essential infrastructure, and for various other reasons.


Housing conditions have greatly improved in the affluent industrial nations throughout the second half of the twentieth century, but more than two-thirds of the households in the world are in developing countries, the great majority of them in rural areas. The most prevalent indoor environment in the world is the same now as throughout history—huts in rural communities.1 This is changing, as urbanization transforms the distribution of populations in the developing world, where the proportion living in urban areas by the beginning of the new millennium had reached almost 50%.2 The urban population will compose 65% or more by 2025 (UN World population and urbanization trends, Many cities are already very large (Table 51-1).


Many new urban dwellers in developing countries have terrible living conditions, crowded into periurban slums. They often ...

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