Chronic non-communicable and communicable diseases like hypertension, diabetes, intentional and unintentional injuries, tuberculosis, rheumatic heart disease, and HIV infection are recognized to exist in slums because of the late complications of these diseases that the formal health sector sees and deals with. However, in slums, little is known about the magnitude, distribution, and risk factors for these illnesses before they manifest as stroke, myocardial infarction, kidney failure, suicide, multidrug-resistant TB, heart valve disease, and AIDS (see Table ).
Diseases that are chronic or associated with chronic conditions whose complications or end-stage outcomes require long-term medical intervention by the formal health sector services.
In fact, it was not until the United Nations Human Settlements Program (UN-Habitat) report of 2003 that a comprehensive global description of slum communities became known [3
]. The report describes in detail demographic, spatial, legal, economic, and social indicators of almost 1 billion people who satisfy the operational definition of slum dwellers. The report attempts to identify different approaches to address this problem to achieve the United Nations Millennium Declaration targets. It stresses participatory slum upgrading and poverty reduction programs. However, one major indicator not assessed in this global survey is health. Apart from the standard social indices, such as life expectancy at birth and under-five mortality rate, and access to improved water sources and sanitation, the report does not address disease spectrum or burden in these communities.
Because slum dwellers are intimately, if not formally linked economically, socially, and culturally to the rest of the urban population, the formal health sectors inevitably end up dealing with the consequences of the chronic diseases described above (Table ). They deal with them at a tremendous cost to the national health system because they see these people only after they develop severe, near end-stage complications of the chronic diseases they have. For example, Brazil is estimated to expend $51,000,000 per year for surgical repair of heart valve diseases caused by the complications of a preventable disease–acute rheumatic fever–that occurs predominantly among slum children [9
]. Those who receive an artificial valve then require life time care to prevent thromboembolism and infection, further contributing to health care cost. Many of these artificial valve recipients later require a second replacement of the valve. Little is known about the reservoir from which these cases arise or factors in the slums that lead to rheumatic heart diseases.
In fact, in many countries, most disease burden or mortality information on slum dwellers is largely based on clinic, hospital, or national mortality registry data. These end point data represent only the "tip of the iceberg". This type of information is not sufficient to plan health care expenditures, and grossly underestimates or misdirects the health care resource allocation needs.
We illustrate one example. In Salvador, the third largest city in Brazil, 60% of the 2.6 million inhabitants reside in slum communities defined by the census bureau as favelas
]. One state infectious disease hospital is mandated to receive patient referrals from the city and its surroundings for all suspected cases of meningitis, leptospirosis, and meningococcal disease, regardless of their socioeconomic affiliation. Leptospirosis, transmitted by a spirochete excreted in rat urine, is a lethal disease (15% case fatality) in patients who present with severe manifestations such as acute renal failure, jaundice and pulmonary haemorrhage. Yet it is an entirely preventable disease. Active hospital-based surveillance initiated in 1996 found that the incidence of severe leptospirosis was 10 per 100,000 population. The major risk factor for acquiring severe manifestations of this disease was to be a resident of a favela
]. More than 95% of these cases come from the city's various favelas
. This observation led the investigators at the Oswaldo Cruz Foundation, Brazilian Ministry of Health to examine risk factors for this disease in one favela
called Pau da Lima, a community of 58,000 people in Salvador (see Figure ). A prospective cohort study found that the disease burden at the community level is significantly greater than that identified at the infectious disease referral hospital. Among inhabitants of this community, 5% are infected with the pathogenic spirochaete each year (unpublished results). Although all cohort subjects were favela
residents, those who resided in close proximity to an open sewer were the major risk group for acquiring infection. These observations could not have been made by hospital-based or formal health sector-based disease surveillance.
Furthermore, in the process of performing this community-based study, the field team discovered that a large proportion of the residents of this shantytown suffered from a variety of chronic illnesses, both infectious and non-infectious. These included hypertension, diabetes, asthma, pyoderma secondary to scabies skin lesions, intentional and unintentional injuries and their chronic sequelae, mental illnesses, complications of drug and alcohol use, sexually-transmitted infections, and reproductive health problems. When community leaders of Pau da Lima were asked what they considered to be the most important health problems in their community, they reported hypertension, leptospirosis, and diabetes. They did not report diarrhea, tuberculosis, or acute respiratory infections–diseases frequently considered to be important in developing countries by developed country investigators. At the insistence of the community leaders, the Oswaldo Cruz Foundation performed a large hypertension screening survey among Pau da Lima residents and identified that hypertension rates (18% above 18 years of age) approached those observed in industrialized countries. More recently, obesity has become recognized in this population as a chronic condition. At this time, little is known about the burden of all the cases of stroke, congestive heart failure, kidney failure, rheumatic heart disease, and other complications that arise from this population in Salvador that the formal health care services manage.
In most cities of the world, slums, by definition, are informal and illegal settlements. A large proportion of the residents are rural migrants, displaced persons, illegal and legal immigrants, unemployed, and refugees. They are not necessarily all poor. There are those who are legally employed in formal sector occupations, such as school teachers and even university instructors, as well as those who are self-employed and own businesses [1
]. However most are employed in low-paying occupations, such as in domestic services, the garment industry, solid waste recycling, security service, and day labor; even crime constitutes a type of income-generating activity for some residents [1
]. Nearly all of these people are excluded from the usual benefits provided to or required for the formal sector employees, including minimal wage compensation, pension, let alone health insurance.
The world's urban population is increasing by about 70 million people a year [3
]. These people require housing, employment, and services. The inability of governments in developing countries to meet their needs forces them to rely on or create their own informal infrastructure. Informal housing, informal employment, and self-employment are some of the survival activities adapted by these urban dwellers that are somewhat within their own power to implement. Over several decades, the largest favela
in Rio de Janeiro called Rocinha has evolved from a squatter community predominantly consisting of wooden shacks, dirt and gravel streets and alleys, to a community with predominantly concrete and brick houses, paved streets, metered electricity, and piped water [1
]. Even private banks and businesses have moved in [1
]. Much of this transformation took place through the actions of community associations and other self-empowerment organizations that took advantage of their large population size as an economic incentive to lure in formal sector businesses and service providers [1
]. Similar transformations have taken place in other shantytowns in major urban centers, especially in Asia and Latin America.
However, of all the basic human services available to slum dwellers, one that is beyond the control of these residents is health service. Health service, by definition, requires specialized, skilled, or trained personnel. It requires an infrastructure for delivery of care that involves provision of specialized information, physical examination, diagnostic services, hospitalization, medications, follow-up care, prevention, and surveillance. None of these services can be provided or created by the slum dwellers themselves. Furthermore, unlike electric or water companies, banks, or other private businesses, health service providers have little or no economic incentive to move into slums. Apart from those provided by volunteer groups, nongovernmental organizations (NGOs), and fee-for-service private clinics and pharmacies (usually run by unlicensed or poorly trained professionals or even nonprofessionals), health services are virtually nonexistent within most of the world's slums. Hence, health service is a social service that can only exist in the formal sector upon which the slum dwellers are completely dependent when they develop an end-stage disease.
While the world's governments worry and spend billions of health dollars in preparation for the uncertain Avian influenza pandemic and intentional release of pathogens, the world awaits a certain and unprecedented epidemic of chronic communicable and non-communicable diseases smoldering among burgeoning slum populations worldwide [4
]. For emerging economy nations like Brazil, China, India, Thailand, and Mexico, this problem may reverse all the economic gains made in the last 2 decades, just as AIDS did to Africa in the last 20 years. Slum dwellers comprise a distinct urban population, whose health assessment and needs require novel approaches and focused solutions that cannot await the elimination of poverty and inequality [12
]. While poverty reduction, self-empowerment, and elimination of disparity are important and worthy goals for improving health care in these communities, the speed of development and size of urban slums render achievement of these goals enormously challenging. Adequate and just characterization of the determinants of chronic and acute diseases in slums requires long-term prospective population-based surveillance. It also requires new science to understand social-cluster determinants of diseases. This is also challenging and expensive. But further neglect of this neglected population is likely to become even more costly.