In 2008, the proportion of the world population living in urban areas crossed the 50% mark. Growing urbanization is a recent phenomenon in the developing world. The proportion of urban population in India has increased from 10.84% in 1901 to 27.8 % in the year 2001. This means that urban population in India in 2001 was 285 million.

This increase in urban population has been attributed both to natural growth and migration from villages because of employment opportunities. When villagers arrive, many find only illegal and unplanned housing that lacks basic public infrastructure. This transition is happening chaotically, resulting in a disorganized urban landscape, and constitutes a social crisis that could result in a major health disaster. The United Nations Human Settlement Programme reports that 43% of urban residents in developing countries such as Brazil and India live in such slums.

For a city to be sustainable, the health of its inhabitants is of paramount importance. With unprecedented growth and spread of human population, infectious diseases contribute significantly to illnesses around the world. Ecological changes play a major role in the emergence of infectious diseases, and urbanization has been associated with outbreaks and emergence of many infections around the world. The outbreak of SARS in Hong Kong in 2002 and 2003, which was believed to have originated in rural China, demonstrated how dense urban living could ignite a global health crisis. In a slum, the lack of surveillance and adequate healthcare result in more rapid spread of disease.

This massive urbanization in developing countries has significant public health implications, including the emergence of infectious diseases transmitted through air or water, as well as those transmitted by insects and animals. The impact of these diseases is compounded by inadequate infrastructure and poor healthcare systems available. Urban slums in tropical developing countries are particularly at high risk from outbreaks of diseases such as tuberculosis, malaria, dengue cholera, typhoid and plague. This is due to the combination of frequent flooding, warm temperatures, poverty, high population density, poor hygiene, poor sanitation, inadequate sewage facilities and waste disposal, poor drainage, and abundance of rats and stray dogs.

In fact, mortality among children under five years of age and among infants is higher in urban slums than in rural settings. Care-seeking patterns show that although less expensive, higher quality government clinics are often available, slum residents choose more expensive private providers for a multitude of reasons—from perceived quality to ease of access. One study, which examined the care provided by private practitioners in Mumbai, found 80 different regimens being used for tuberculosis, only four of which met the guidelines of the World Health Organization.

In many cases new interventions are required but in others, interventions that are known to be effective need to be translated into effective programmes. Effective public health services such as vaccination, safe water supply, good sewage facilities and sanitation are all required.

As the world becomes more urban, the health of the urban poor may suffer. Progress that has been achieved in public health could be erased and the stage set for devastating pandemics of infectious diseases.

Sandeep Guleria is additional professor, department of surgery, All India Institute of Medical Sciences, New Delhi.