The 21st century health challenge of slums and cities.

One of the key 21st century challenges in population health is the challenge of improving the global urban condition. 2 Starting in 2007, and for the first time in human history, the majority of the world's population will live in urban areas. According to the latest UN projections, 3 by 2030, the world's urban population will increase by more than two billion, while the rural population will decline by about 20 million. This shift is largely the culmination of a rapid global urbanisation process that has been underway for more than 250 years. Rapid urbanisation first became manifest in the countries undergoing industrialisation in the developed world, and then in Latin America. Today its prime locus is the poorer parts of Asia and Africa. More than 90% of the world's urban population growth by 2030 will be in less developed regions. Any effort to measurably improve global health outcomes, especially in these regions, will need to address urban reform. According to estimates prepared by the UN Human Settlements Programme (UN-HABITAT), about a third of the world's estimated 3 billion current urban residents dwell in slums, or places characterised by one or more of these shortcomings: insecurity of tenure, poor structural housing conditions, deficient access to safe drinking water and sanitation, and severe overcrowding. 4 All these factors have direct consequences for the physical and psychological well-being of the urban population. Barring determined policies to improve housing conditions and income earning opportunities for the poorest urban residents, the health situation accompanying contemporary urban life will exhibit worsening morbidity and mortality for several communicable and non-communicable health problems and diseases. Poorer families consistently have higher birth rates, and most rural-urban migrants in low-income and middle-income countries are poor. 5 Even under the assumption that the proportion of slum dwellers within the total urban population does not increase but instead remains constant, we can still project that by 2030, close to 1·7 billion of the expected 3·93 billion urban dwellers in low-income and middle-income countries will be living in slums. 5 According to this bleak no-action scenario, a conservative estimate is that the slum population in low-income and middle-income countries is likely to double in less than 30 years. 6 Communicable diseases are a major problem in urban populations in general and slum populations in particular. Close to half the urban population in Africa, Asia, and Latin America have one or more of …