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The World Health Organization defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.”1 The key message of this definition is that health is a holistic measure that is influenced by socioeconomic factors and inequality. Public health is a discipline in which the level of focus is on the health of populations as opposed to that of individuals, as is the case in clinical medicine. A useful definition of public health is as follows:
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Public health is the science and the art of preventing disease, prolonging life, and promoting physical health and mental health and efficiency through organized community efforts toward a sanitary environment, the control of community infections, the education of the individual in principles of personal hygiene, the organization of medical and nursing service for the early diagnosis and treatment of disease and the development of the social machinery to ensure to every individual in the community a standard of living adequate for the maintenance of health.2
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This definition articulates some of the roles of public health practitioners in relation to society and health. It also highlights the four key areas of public health action: (1) preventing disease and promoting health, (2) improving medical care, (3) promoting health-enhancing behavior, and (4) modifying the environment.3
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As early as in the fifth century bc, Hippocrates suggested a clear link between environmental factors and disease states. In more recent centuries, the physician John Snow helped to establish the field of public health during the 1854 London cholera epidemic.4 By carefully counting the number of deaths from cholera according to population denominators in specific London districts, he was able to establish that household water supply might be the key common factor leading to cholera deaths. Snow hypothesized that cholera was a water-borne disease, ...