Cities, urbanization and health.

It is in cities, and not the countryside, where the human ‘creative flame’ has burnt most brightly. For millennia they have been the centres and drivers of commercial, scientific, political and cultural life, having major influence upon whole countries and regions. The positive and progressive aspects of cities and urban centres recognized by historians, economists and other social scientists contrast with the more pessimistic tone of much of the epidemiological and public health literature on cities and urban life. In part this derives from the iconic place in our discipline of accounts of poor urban health in the 19th century in countries such as Britain. Almost everyone who has taken a course in epidemiology will have come across John Snow’s classic studies of cholera in London in the 1840s, with its attendant images of poor sanitation and contaminated water. This history finds a resonance in contemporary concerns about the impact of cities and urbanization on health today. First, there are the health and social problems of inner-city areas of high income countries such as drug addiction, violence and HIV/AIDS. Second, there is concern about the health and welfare of the growing number of people in low and middle income countries who are living in urban areas— many of whom are in what are classified as slums. Third, as mentioned by Dr Chan the WHO Director General in the 2007 World Health Report, increasing global urbanization is classed as a threat to ‘Public Health Security’ as the unprecedented level of population agglomeration may facilitate the spread of epidemic diseases. Finally, there is the plausible connection between urbanization and the rising levels of non-communicable diseases in low and middle income countries. This editorial sets out to challenge the largely negative view of the population health impact of cities and urbanization in the contemporary world. While there are real urban threats to health, on balance cities and urban living today have important health advantages particularly in the developing world. It is desirable that epidemiologists and public health advocates develop a better and more informed understanding of the nature of urbanization and the differences between urban and rural life today. In particular careful study is required of the way in which urban–rural differences in disease risk are heterogeneous and often context-specific.