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close this bookFact sheet No 122: Cities and Emerging or Re-emerging Diseases in the XXIst Century - June 1996 (WHO, 1996, 3 p.)
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View the documentCities and Emerging or Re-Emerging Diseases in the XXIst Century
View the documentEmerging and Re-Emerging Diseases
View the documentEnvironmental Health
View the documentThe Health of Women and Children in Tomorrow’s City

(introduction...)

June 1996

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© WHO/OMS, 1998

Cities and Emerging or Re-Emerging Diseases in the XXIst Century

The world’s urban population in 1996 is around 2.6 billion people, two thirds of whom live in the South. Urban-dwellers have multiplied more than four-fold over the last 50 years and now represent about 45 percent of the world’s total population. Cities, by concentrating people, increase the possibilities for transmission of infectious diseases. Where there is inadequate provision for water, sanitation, and garbage collection, disease-causing agents - or the vectors or animal hosts on which they rely - can proliferate. The emergence of new infectious diseases and the resurgence of other infectious diseases makes achieving healthy cities more difficult as health care systems prove unable to cope, or as the disease-causing agents or their vectors develop a resistance to public health measures. Without good management, cities become dangerous and unhealthy places.

Emerging and Re-Emerging Diseases

Twenty years ago, many health specialists thought that public health measures could soon limit the importance of infectious diseases. Yet today they remain the world’s leading cause of death, killing at least 17 million people a year. One problem is the emergence of new infectious diseases, at least 30 previously unknown diseases having emerged since 1973. Another is the re-emergence of infectious diseases previously considered as under control. Epidemic cholera, for instance, was again reported in the Americas in January 1991 after being absent for many decades; between 1991 and December 1995 more than 1.3 million cases were reported and upwards of 11,000 deaths. For nearly half a century yellow fever has been considered a rural disease. But many cities, especially in the Americas, have become infested with the Aedes aegypti mosquitos which transmit the disease and are once again at risk.

Other diseases are re-emerging because the pathogen or the vectors that transmit them have become resistant to control measures. Malaria still kills more than a million people each year (mostly children) with a total of 250-450 million clinical cases annually. Although malaria has long been considered mainly a rural disease, it has become one of the most serious health problems in many urban centres where the anopheline mosquito can find standing water in which to breed. Dengue and dengue haemorrhagic fever, also spread by Aedes mosquitoes, are growing problems, the number of outbreaks and epidemics having increased significantly in the last decade. Tens of million of cases occur each year, most of them unreported, causing 500 000 hospitalizations and more than 20,000 deaths. Some 2 billion people worldwide are at risk, mostly in urban areas.

Urbanization concentrates large numbers of people particularly vulnerable to infection. The numbers of older people and of persons with HIV, two categories who are more vulnerable to many infectious diseases, are also increasing in towns. People are constantly moving in or out of cities, which can mean the arrival of newcomers who bring new infections to which the city population has little or no immunity. The rapid increases in travel and trade over the last few decades have increased opportunities for pathogens and vectors to spread to new areas. The mosquito responsible for transmitting dengue fever in Asia has become established in the United States, Brazil and parts of Africa. Anopheles stephensi, the principal vector for urban malaria, has adapted to the urban environment in India and the Eastern Mediterranean region, while other species have adapted to breed in swamps and ditches around urban areas in Nigeria and Turkey.

In the early decades of antibiotic use, public health specialists did not foresee the ability of many agents of infectious diseases to rapidly develop resistance to the drugs or chemicals that had previously killed them. The problem has been exacerbated in countries where antibiotics are overused and misused and where governments have not sufficiently prioritized disease control programmes. One example is tuberculosis, which is responsible for some 3 million deaths each year and is the single largest cause of adult death in the world, mainly among populations living in the poorest areas. In urban areas, a combination of overcrowding and poor ventilation often means that one person with tuberculosis, if not detected and cured, will transmit the infection to 10-15 other people each year -- and often to family members. The burden of tuberculosis has increased rapidly over the past decade or so, partly linked to the spread of HIV/AIDS. Most deaths from tuberculosis occur in the South, but they have also increased in many wealthy nations during the 1980s and early 1990s after decades of steady decline. WHO’s directly observed treatment, short course (DOTS) strategy aims at curing tuberculosis patients in all settings, including urban areas, and if adopted will effectively prevent the emergence of drug resistant strains of tuberculosis.

Environmental Health

Every year more than 5 million people die of illnesses linked to unsafe drinking water, improper excreta disposal and unclean domestic environments - again, most of them in the South. Diarrhoeal diseases remain among the most prominent causes of premature death and illness in many urban areas. The proportion of urban dwellers with provision for piped water and sanitation has improved considerably since the first UN Conference on Human Settlements, Habitat I, was held 20 years ago. However, with the rapid increase in urban populations, the absolute number of people not served by water supplies and sanitation has increased, not declined. In 1994, close to 300 million urban dwellers still had no proper water supply. Similarly, more than 600 million urban dwellers lack provision for sanitation which is easily accessible, reduces the possibility of human contact with human excreta, and is easy to maintain.

WHO guidelines or national air quality standards are oftentimes not met, and more than 1.5 billion urban dwellers are exposed to levels of ambient air pollution which are above the recommended maximum levels. Worldwide, about 400 000 additional deaths are attributable each year to air pollution. Air pollution control, the implications and priorities of which vary from country to country, involves coordination among sectors such as industrial development, city planning, water resources development and transport policies.

The Health of Women and Children in Tomorrow’s City

A large part of the world’s children live in overcrowded, poor-quality shelters, with several persons to each room and no piped water or adequate sanitation. Too often, people cannot turn to health services when their children are sick or injured. In such circumstances, one child in two may die before his or her fifth birthday.

Among households living in the poorest quality accommodations in Africa, Asia and Latin America, the proportion of infants who live and die of infectious and parasitic diseases is several hundred times higher than for households in Western Europe or North America. Most of these deaths are due to diseases that are easily prevented or cured. In the South, diarrhoeal diseases remain among the major causes of infant and child death in many urban areas, although good housing conditions and health care could prevent this. Children are more vulnerable to respiratory disease, and a child weakened by frequent illness and poor nutrition is more vulnerable still. Acute respiratory infections, mainly pneumonia, remain the largest cause of death in many urban areas and are aggravated by poor ventilation. Even so, such infections are easily cured if diagnosed quickly and treated properly. A child who contracts bronchitis or pneumonia in the South is 50 times more likely to die than a child in Europe or North America. Measles and tetanus also remain major causes of child death yet both are preventable by immunization.

Gender inequality may in extreme cases lead to prenatal selection in favour of boys, or female infanticide. Men and boys often receive preference within households, including higher expenditures on medicines and health care when sick or injured. Girls’ nutritional and health needs, including immunization, often receive a lower priority than boys’. These discriminatory practices have serious implications on how girl infants and young children cope with disease and the impact of environmental hazards. For “children of the street”, or abandoned children, hazards to health are obviously much greater. They generally have poor quality accommodation (often sleeping in the open or in public places) and difficulties in getting access to latrines, health services and places to wash and obtain drinking water. They are also exposed to child abuse, not least when child prostitution - and its corollary of sexually transmitted diseases - is one of the ways of ensuring sufficient income for survival.

The health of children is closely linked to that of the women who care for them. Illiteracy among women deprives them of information that is central to their understanding of how their bodies function and how they can prevent diseases and protect themselves - and protect their children. To address the health needs of women, those responsible for health care and for other aspects of the urban environment must reach a better understanding of women’s needs and priorities. Between Habitat I, the first UN Conference on Human Settlements in 1976, and Habitat II in 1996, a critical change in emphasis occurred, away from stating what national governments should do towards a support of national and provincial governments to the initiatives of those living and working in cities. One such example is the range of innovations developed in Guatemala City within illegal settlements, which included women being chosen by their surrounding households to be trained as health promoters and new models of community-based care. Improving women’s health depends not only on improved health services, housing and basic services, but also on meeting needs such as increased access to resources, education and employment and to the promotion of human rights and fundamental freedoms.