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World Resources 1996-97
(A joint publication by The World Resource Institute, The United
 Nations Environment Programme, The United Nations Development
 Programme, and the World Bank)
(Data edited by Dr. Róbinson Rojas)

2. Urban Environment and Human Health


Differences Among Cities

Urban residents in developing countries have a far greater burden of premature death and disease than do their counterparts in developed countries, reflecting broadly their relative poverty and inadequate access to basic services and opportunities. Yet, even within those broad categories of developed and developing countries, cities differ widely in their health profiles. Profiles depend broadly on several factors: the mix of environmental risks faced (physical, biological, and social), the proportion of the population facing different risks, the demographic profile of the city and of groups within it, and access to health services. All of these tend to shift with development and increasing wealth.

Since the mid-19th Century, when improvements in the handling of urban water and sewage began to take hold, the burden of communicable diseases has steadily declined throughout many cities in the developed world. The major causes of death are now chronic and degenerative diseases--primarily heart disease and cancer--tha t are related to such social factors as diet, stress, and lifestyle. And, recently, violence and accidents have become increasingly significant causes of death in cities.

This shift from communicable to noncommunicable diseases has been described as the "epidemiological transition" or the "health transition" (3). This transition, which is not unique to urban areas but which typically occurs first and fastest there, is related to several factors. One is exposure to the risk factors for disease, which change as countries urbanize and develop. Access to effective health services is clearly a second major factor (4). Finally, the aging of the population, which is in turn related to mortality and fertility rates, is also a critical determinant, since the incidence of chronic and degenerative diseases typically increases with age (5).

Signs of this health transition are now apparent throughout cities of the developing world. In some cities, especially the economically advanced ones, heart disease and cancer are emerging as major causes of death, as they already have in the developed world. Indeed, in cities as diverse as Sao Paulo, Brazil; Cape Town, South Africa; and Accra, Ghana, heart disease and cancer are now leading causes of death, just as they are in London and Washington, D.C. (6) (7) (8) (9). Violence has now reached epidemic proportions in some urban centers in South America as well as North America (10) (11) (12) (13) (14) (15).

The health transition, however, is by no means complete in most cities in the developing world. In fact, the image of a smooth transition from communicable to noncommunicable diseases as development progresses does not seem to fit the evolving health profiles of these cities, many of which are struggling with high incidences of both types of problems.

Although data on overall causes of death in urban areas of the developing world are sparse, they present a general picture of urban populations in developing countries suffering the "worst of both worlds" in their mortality profiles. In other words, for residents of cities in developing countries, the burden of communicable diseases, related to poverty, combines with risks of chronic diseases, associated with social conditions, to create a double burden of ill health (16).

These changing patterns of health in urban areas can be seen by examining data on the causes of death in three very different cities: Accra, Sao Paulo, and Prague, Czech Republic. (See Figure 2.1.)The health profile depicted for each urban center reflects not only the impact of environmental health policies pursued in the past but also the importance of the demographic mix in particular urban centers.

In both Prague and Sao Paulo, two economically advanced cities, the proportion of deaths attributable to infectious and parasitic diseases is now extremely low for the overall population (0.3 percent in Prague and 4 percent in Sao Paulo)(17) (18). To a great extent, these statistics illustrate the level of wealth of each urban center and the relative success of past initiatives for improving urban health conditions. Both Prague and Sao Paulo have made efforts to provide comprehensive water and sanitation coverage, along with vaccination programs for preventable infections and basic health services.

In Accra, the picture is somewhat different: infections (largely diarrheal diseases, malaria, and measles)account for 18 percent of all deaths (19). Limited access to basic water and sanitation facilities explains part of the profile within Accra. Yet, demographic factors are also important. Of the three cities, Accra contains the largest proportion of children under age 5, and young children are most vulnerable to the risk of death from infections.

Respiratory diseases are significant in all three cities, accounting for 12 percent of all deaths in Accra and Sao Paulo and 3.5 percent in Prague (20) (21).

In both Accra and Sao Paulo, diseases of the circulatory system are the primary cause of death in the population as a whole (24 and 33 percent of all deaths, respectively) (22). In Prague, as in most developed cities, the proportion is even higher (54 percent). Accidents and violence emerge as more important than infections or respiratory conditions in both Prague and Sao Paulo (23) (24).

Differences Within Cities

Perhaps as striking as differences among cities is the variation in health among different groups within the same city. This variation within cities flies in the face of conventional wisdom about the effect of urbanization on health. Until the late 1970s and early 1980s, urbanization was viewed as a consistently positive force for improved health, largely because it resulted in better access to health services.

Comparisons of average urban health figures with average rural figures suggest that this is so, but such comparisons conceal gross health inequalities within the urban population (25) (26) (27). In many cities in developing countries, evidence now suggests that health conditions for the urban poor are sometimes worse than they are for their rural counterparts (28) (29) (30). (See Figure 2.2.)

In the developing world, mortality rates are significantly higher for children in squatter areas of cities than for children living in nonsquatter areas (31). For example, in Tondo, a large squatter settlement in Manila, Philippines, infant mortality rates are nearly three times greater than those in nonsquatter sections of the city. In addition, the incidence of diarrhea in Tondo (adults and children) is two times higher and the incidence of tuberculosis is nine times higher than in wealthier sections of Manila (32). In interpreting environmental health differentials, it is important to keep in mind that poor people in general tend to be more vulnerable, both physically and economically. With their greater levels of exposure to poor sanitation, overcrowded conditions, inadequate nutrition, social stresses, and environmental pollutants and their limited access to health care, they are more likely both to get sick and to remain sick. Moreover, the economic consequences of illness tend to be more serious among the poor, often undermining the already fragile finances of the household. The financial loss that occurs when an income earner is ill or when medical bills must be paid can help create a cycle of poverty and chronic ill health (33).

Nor are the health differentials between wealthy and poor confined to the developing world. In cities in developed countries as well, the poor show disproportionately high rates of death and disease for a range of problems. For example, in New York City, children in overcrowded poor households in the Bronx have a fivefold greater risk of contracting tuberculosis than their better-off neighbors (34). In London, there are twofold health differences in rates of heart disease, tuberculosis, and other respiratory diseases between those living in poor areas and their wealthier neigh bors (35). Similar patterns can be discerned in social risks too. In Kansas City, Missouri, in the central part of the United States, African- American adolescents (12- to 16-year-olds), who tend to live in poorer areas, have a 13-fold greater risk of injury from firearms than white adolescents (541 compared with 42 per 100,000 persons per year)(36).

Urban violence tends to concentrate in particular areas of cities and towns. In a 1990 study, mortality rates among African Americans in Harlem were found to be the highest in New York City--and 50 percent higher than those of all African Americans. The study's authors conclude that the mortality rates among people in Harlem justify classifying Harlem as a natural disaster area. Survival analysis showed that men in Harlem were less likely than men in Bangladesh to reach age 65 (37). Data on the distribution of violence within cities in the developing world are sparse. In Cape Town, however, homicides account for 19 percent of deaths in the black community, but just 8 percent of deaths in the city as a whole (38).

The Special Vulnerability of Children and Women

Even among the poor, certain groups are more susceptible to both biological and social risks than others. The very young and the very old, for instance, tend to be more susceptible to infectious diseases and are more likely to die if they do become ill.

Studies show that the increased health risks that impoverished children face in cities can be significant. Children are exposed to a barrage of infectious agents and toxic contaminants during play, at meals, and at school or other communal activities (39). Intestinal disorders such as severe diarrhea, caused by a variety of bacteria, viruses, and parasites, are among the most prevalent and serious health risks to children exposed to poor sanitation or contaminated water supplies. Of the 5 million children who are estimated to die annually of diarrheal diseases in the developing world, the majority come from poor urban families (40).

Respiratory infections, which are the second most common cause of death among children in the develop ing world (41), a lso pose a particular risk to children in urban settings, with overcrowding and air pollu tion--both indoors and outdoors--being two significant contributors to this risk. Overcrowded conditions increase the levels of exposure to infected individuals, which facilitates the more rapid dissemination of respiratory diseases (42).

Indoor and outdoor air pollutants can damage children's lung tissues, predisposing them to viral or bacterial infections. There is also evidence that urban environmental factors associated with lower-income settings can aggravate, and perhaps even initiate, childhood asthma. These factors include indoor pollutants from cooking fires, coal-fired heaters, secondhand cigarette smoke, and other sources, as well as allergens associated with dust mites and cockroaches (43) (44) (45).

Infant and child death in poor settlements is often not simply the result of a discrete disease but the outcome of a series of health problems. This typically involves an interplay of malnutrition, a variety of infectious diseases, and, possibly, exposure to chemical pollutants. Lack of health care increases vulnerability.

Social factors, too, can be important in increasing the health risks that urban children face. Adolescents seem to be particularly affected by inadequate urban social environments. Data from some cities in North and South America suggest striking, age-specific problems with homicides among young men and boys. In public health terms, violence now overshadows infectious diseases as a cause of death among older children in some urban environments (46) (47). For example, violence--mostly homicides--accounted for 86 percent of all deaths of boys ages 15 to 19 in Sao Paulo in 1992 and more than half of all deaths among 5- to 14-year-old boys (48).

Urban women also face increased health risks, largely because of their social and economic roles, which expose them to greater numbers of environmental hazards. Women are usually responsible for taking care of sick children, increasing their direct exposure to disease-causing organisms. They usually take primary responsibility for obtaining water and washing laundry--activities that can be hazardous where sanitation is poor, washing facilities are inadequate, and water supplies are contaminated (49). As the household food preparer, urban women in the developing world are often exposed to very high levels of smoke from cookstoves, which also put them at risk of receiving burns.

Physiological factors also play a part in making women's health more vulnerable. Women are particularly at risk during pregnancy and after childbirth, being more vulnerable to some chemical toxins and more susceptible to certain diseases, such as malaria (50) (51).

The kinds of employment that women have access to often put them at risk as well. Many urban women in developing countries work in small-scale industries where toxic chemicals are often used without adequate safeguards. Piecework done at home, such as fabricating sandals or articles of clothing, is a common source of income among urban women and can involve the use of dangerous adhesives and other flammable or toxic materials (52). Risks to women due to chemical exposure, repetitive motion, or stress are high even in many modern urban industries such as microelectronics and large- scale garment manufacturing, where women make up a high percentage of the work force (53). Prostitution, with its predominantly urban focus, is associated with a host of health risks, from sexually transmitted diseases such as AIDS and gonorrhea to physical abuse.

Social factors are especially important contributors to the increased health vulnerability that urban women experience. Violence against women--within and outside of the home--has been increasingly recognized as a prime threat to women's health in both the developed and the developing world (54). Although this is by no means a strictly urban phenomenon, its incidence is high in cities and may be increased by psychosocial factors such as stress associated with poor urban housing, inadequate income, and lack of equal opportunity to employment or education, although the precise links between these stresses and violence are not well defined (55).

References and Notes

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