Public health is concerned with threats to the overall health of a community based on population health analysis. Health is defined and promoted differently by many organizations. The World Health Organization, the United Nations body that sets standards and provides global surveillance of disease, defines health as: "A state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Public health experts agree this definition is incomplete. Other components included in an individual's health are nutritional, spiritual, and intellectual.
The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). Public health has many sub-fields, but is typically divided into the categories of epidemiology, biostatistics and health services. Environmental, social and behavioral health, and occupational health, are also important fields in public health.
An alternative definition by Winslow from Modern Medicine in 1920 is: "the science and art of preventing disease, prolonging life and promoting health through the organised efforts and informed choices of society, organisations, public and private, communities and individuals."

Objectives
In some ways, public health is a modern concept, although it has roots in antiquity. From the early beginnings of human civilization, it was recognized that polluted water and lack of proper waste disposal may spread vector-borne diseases. Early religions attempted to regulate behavior that specifically related to health, from types of food eaten, to the extent which certain behaviors could be indulged, such as drinking alcohol or sexual relations. The establishment of governments placed responsibility on leaders to develop public health policies and programs to gain some understanding of the causes of disease to ensure stability, prosperity, and maintain order.

History of public health
By Roman times, it was well understood that proper diversion of human waste was a necessary tenet of public health in urban areas. The Chinese developed the practice of variolation following a smallpox epidemic around 1000 BC. An individual without the disease could gain some measure of immunity against it by inhaling the dried crusts that formed around lesions of infected individuals. Also, children were protected by inoculating a scratch on their forearms with the pus from a lesion. This practice was not documented in the West until the early-1700s, and was used on a very limited basis. The practice of vaccination did not become prevalent until the 1820s, following the work of Edward Jenner to treat smallpox.
During the 14th century Black Death in Europe, it was believed that removing bodies of the dead would further prevent the spread of the bacterial infection. This did little to stem the plague, however, which was most probably spread by rodent-borne fleas. Burning areas of cities resulted in much greater benefit, since it removed the rodent infestations. The development of quarantine in the medieval period helped mitigate the effects of other infectious diseases. However, according to Michel Foucault, the plague model of governmentality was to be opposed to the later cholera model. Cholera, which second pandemic devastated Europe between 1829 and 1851, was first fought by the use of what Foucault called "social medecine", which focused on flux, circulation of air, location of cemeteries, etc. All those concerns, born of the miasma theory of disease, were thus mixed with urbanistic concerns of the management of populations, which Foucault designed by the concept of "biopower". The German conceptualized this in the Polizeiwissenschaft ("Science of police").
The science of epidemiology was founded by John Snow's identification of a polluted public water well as the cause of an 1854 cholera outbreak in London. Dr. Snow believed in the germ theory of disease as opposed to the prevailing miasma theory. Although miasma theory taught correctly that disease is a result of poor sanitation, it was based only upon the prevailing theory of spontaneous generation. Microorganisms, which are now known to cause many of the most common infectious diseases, were first observed around 1680 by Anton van Leeuwenhoek. But the modern era of public health did not begin until the 1880s, when the culmination of Robert Koch's germ theory and Louis Pasteur's production of artificial vaccines revolutionized the study of infectious disease.

Modern public health
Today, most governments recognize the importance of public health programs in reducing the incidence of disease, disability, and the effects of aging, although public health generally receives significantly less government funding compared with medicine. In recent years, public health programs providing vaccinations have made incredible strides in promoting health, including the eradication of smallpox, a disease that plagued humanity for thousands of years.
One of the most important public health issues facing the world currently is HIV/AIDS. Tuberculosis, which claimed the lives of authors Franz Kafka and Charlotte Brontë, and composer Franz Schubert, among others, is also reemerging as a major concern due to the rise of HIV/AIDS-related infections and the development of strains resistant to standard antibiotics.
Another major public health concern is diabetes. In 2006, according to the World Health Organization, at least 171 million people worldwide suffer from diabetes. Its incidence is increasing rapidly, and it is estimated that by the year 2030, this number will double.
A controversial aspect of public health is that related to the control of smoking. Many nations have implemented major initiatives to cut smoking, such as increased taxation and bans on smoking in some or all public places. Proponents argue that smoking is one of the major killers in all developed countries, and that governments have a duty to reduce the death rate, both through limiting passive smoking and by providing fewer opportunities for smokers to smoke. Opponents say that this undermines individual freedom and personal responsibility (often using the phrase nanny state in the UK), and worry that the state may be emboldened to remove more and more choice in the name of better population health overall. However, proponents counter that inflicting disease on other people via passive smoking is not a human right, and in fact smokers are still free to smoke in their own homes.

Public health programs
The application of economics to the realm of public health has been rising in importance since the 1980s. Economics studies can show, for example, where limited public resources might best be spent to save lives or cause the greatest increase in quality of life.

Academic resources

Airborne diseases
Auxology
Biological hazard
Carl Rogers Darnall
Chief Medical Officer
Committee on the Environment, Public Health and Food Safety
Epidemiology
European Programme for Intervention Epidemiology Training (EPIET)
Environmental health
Food safety
Health Impact Assessment
Health literacy
Health reform
Health policy analysis
Hygiene
Indian health ministry
Infection control
"Typhoid Mary" – an important case of the clash of individual rights and public health
Maternal health
Occupational safety and health
Patient safety organization
Population health
Public health law
Public health laboratories
Public health informatics
Public health in the People's Republic of China
Public Health - Seattle & King County
Reproductive health
Samuel Crumbine
Sara Josephine Baker
Sewer
Social hygiene movement
Vectorborne diseases
Waterborne diseases
Water supply