Medical Geography (Health Geographics) is the branch of Human Geography that deals with the geographic aspects of health (status) and healthcare (systems). It seeks, along with related disciplines such as Medical Anthropology, Medical Sociology and Health Economics, to improve our understanding of the various factors which affect the health of populations and hence individuals. In other words, these interrelated disciplines can enhance the concepts or "models" we have about health and disease, and hence enhance the final outcomes of healthcare.
The concept that place and location can influence health is a very old and familiar idea in medicine. As far back as the time of Hippocrates (c. 3rd century BC), physicians have observed that certain diseases seem to occur in some places and not others. Even within the human body, many diseases and organisms are known to have a predilection for, or to exclusively affect specific body organs or systems (anatomico-physiological "locations" within the human body).
In the following example we will use GIDEON (Global Infectious Disease and Epidemiology Network, an expert decision support system for Windows) to diagnose a simple case of diarrhoea in an infant (< 2 years old). The three screenshots below show the "Diagnosis Results" (with probabilities) for the same patient but with a different country of disease acquisition in each screenshot (France, Egypt, Jordan in this example). You can clearly see how the differential diagnosis and probabilities differ in each case by just changing the geographic location of disease acquisition. You can download GIDEON from the 'Resources' page.
Disease Diffusion (Spread)
People have also been aware of the process of disease diffusion across geographic regions for centuries even during times when aetiology of infectious diseases was a mystery, e.g., the Black Death (plague, 1346-51 AD pandemic, which was carried along trade routes from China to Europe. Frequently, attempts to understand why certain diseases seem to only occur in certain places and not others has lead to new insights into the nature of the disease itself (e.g., environmental and socio-economic causes/factors). In the early part of the 20th century, for example, two dentists in Colorado discovered that children living in areas with high levels of naturally-occurring fluoride in groundwater had reduced dental caries.
In 1854, death and despair engulfed London. In the Soho district, when nearly six hundred people died from cholera in just 10 days, death tolls rang around the clock from the church bell tower. With no known cure, panic spread throughout the city and residents began thinking that they were somehow being infected by the buried corpses of plague victims who died during the European pandemic a century before. Housing had been built on the cemetery where those plague victims were buried. As cholera deaths occurred in these homes, and in homes surrounding the area, the residents feared that they were being infected by vapours coming from the ground.
Dr. John Snow, a London physician and anaesthesiologist, knew that to contain the disease, they would have to locate its source. Using maps showing the locations of water pumps and the homes of people who died of cholera, Snow was able to show that one pump, the public pump on Broad Street, was causing most of the disease. People could also see on this map that cholera deaths were not confined to the area around the cemetery and were therefore convinced that the infection was not due to vapours coming from it.
Snow suspected that infected water from the pump was the cause. He instructed the authorities to remove the handle to the pump, making it unusable; the number of new cholera cases dropped dramatically. The Broad Street pump proved to be the source of contaminated water and hence cholera, just as Snow had thought.
As Geography matured as an academic discipline in the 19th century, it was only a matter of time before geographers would also begin to study systematically the geographic aspects of health and disease. Today, with the growing world-wide incidence of HIV infection, the "return" of infectious diseases such as tuberculosis, and declining health budgets in many countries (especially in tropical regions and the "third world"), the significance of place in understanding health and disease seems stronger than ever.
The Geography of Disease
Physicians, public health professionals and medical geographers measure health strictly in terms of indicators of ill-health such as morbidity (illness and disease complications) and mortality (death). Three allied fields of medicine, namely Epidemiology, Public Health, and Medical Geography are concerned with examining the distribution of disease and death at various geographic scales, in an attempt to determine if the presence or absence of particular illness is associated with some factor(s) in the social or physical environment.
The "Time" Dimension
Mapping vs. Analysing
Although the mapping of disease data can be relatively straightforward, interpreting spatially referenced disease data can sometimes be challenging, particularly for non-infectious and chronic diseases (e.g., coronary heart disease and diabetes mellitus). For example, a researcher might map the distribution of people with schizophrenia (a psychiatric mental disorder) in urban areas and find that they tend to reside in low-income, inner-city areas. At this stage, the researcher can understand how the data is distributed (she can see patterns or clusters — mapping), but explaining why it is distributed as such is another story and requires further research (analysis).
Spatio-temporal analysis is concerned with cluster validation, e.g., that a detected cluster is not due to mere chance factors, and with attribution of detected clusters to the appropriate factors that played a role in their occurrence. Analysis also includes doing comparisons with other relevant patterns/clusters (in the same place at different times and in other places) and again trying to methodically explain any spotted differences or trends. Thus, in the case of the schizophrenia example mentioned above where a cluster or pattern has been detected, many questions arise (new hypotheses) that need to be addressed. For example, does the stress of urban poverty cause mental illness, or are the mentally ill forced to live in cheap housing because their illnesses prevents them from earning a stable income? Or is there a circular relationship between poverty and mental illness?
Although the above example may seem trite, it is important to note that when people become seriously ill, they often 'respond spatially', i.e., they relocate. It is known, for example, that urban residents who contract a terminal disease often move back to their home towns, in order to be cared for by their family and friends in the final stages of the disease.
Regardless of difficulties in data acquisition, map representation, scale, statistical analysis, and the interpretation and utility of results, the study of disease distribution may well be the most challenging and fascinating research area within the entire discipline of geography.
Key Web Sites
Anyone interested in the geography of disease will need a good understanding of the basics of epidemiology, or at least of health statistics. The World Health Organization Web site is a good starting place. The WHO collects mortality and morbidity data from member countries, allowing international and inter-regional comparisons of health and disease. They publish the annual World Health Report, the Weekly Epidemiological Record, WHO Statistical Information System (WHOSIS), and a wealth of other useful publications. The Noncommunicable Disease Division of WHO describes the global epidemiology of diseases such as cardiovascular diseases.
Data on the global epidemiology of cancer can be found at CANCERMondial, a Web site of the International Agency for Research on Cancer (IARC), part of the WHO. The Atlas of Cancer Mortality in the United States (1950-1994) of the US National Cancer Institute is another excellent site worth visiting. Projects are currently being developed to use this exciting resource as a catalyst for research in cancer aetiology and control.
In recent years there has been a great deal of research on the geography of AIDS diffusion, particularly in the United States. The US Centres for Disease Control and Prevention (CDC) provide a wealth of information for public health professionals, including this series of slides on the epidemiology of AIDS. For a dramatic illustration of the impact of the AIDS pandemic worldwide, visit the AIDS Clock of the UNAIDS (Joint United Nations Programme on HIV/AIDS).
An online self-study course on "Epidemiology, the Internet and Global Health" is also available from the University of Pittsburgh (US).