Public Health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals." (1920, C.E.A. Winslow) It is concerned with threats to the overall health of a community based on population health analysis. 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 is typically divided into epidemiology, biostatistics and health services. Environmental, social, behavioral, and occupational health are also important subfields.
The focus of public health intervention is to prevent rather than treat a disease through surveillance of cases and the promotion of healthy behaviors. In addition to these activities, in many cases treating a disease may be vital to preventing it in others, such as during an outbreak of an infectious disease. Hand washing, vaccination programs and distribution of condoms are examples of public health measures.
The focus of a public health intervention is to prevent rather than treat a disease through surveillance of cases and the promotion of healthy behaviors. In addition to these activities, in many cases treating a disease can be vital to preventing its spread to others, such as during an outbreak of infectious disease or contamination of food or water supplies. Vaccination programs and distribution of condoms are examples of public health measures.
Most countries have their own government public health agencies, sometimes known as ministries of health, to respond to domestic health issues. In the United States, the front line of public health initiatives are state and local health departments. The United States Public Health Service (PHS), led by the Surgeon General of the United States, and the Centers for Disease Control and Prevention, headquartered in Atlanta and a part of the PHS, are involved with several international health activities, in addition to their national duties.
There is a vast discrepancy in access to health care and public health initiatives between developed nations and developing nations. In the developing world, public health infrastructures are still forming. There may not be enough trained health workers or monetary resources to provide even a basic level of medical care and disease prevention. As a result, a large majority of disease and mortality in the developing world results from and contributes to extreme poverty. For example, many African governments spend less than USD$10 per person per year on health care, while, in the United States, the federal government spent approximately USD$4,500 per capita in 2000.
Public health plays an important role in disease prevention efforts in both the developing world and in developed countries, through local health systems and through international non-governmental organizations.
The two major postgraduate professional degrees related to this field are the Master of Public Health (MPH) or the (much rarer) Doctor of Public Health (DrPH). Many public health researchers hold PhDs in their fields of speciality, while some public health programs confer the equivalent Doctor of Science degree instead. The United States medical residency specialty is General Preventive Medicine and Public Health.
History of public health
In some ways, public health is a modern concept, although it has roots in antiquity. From the beginnings of human civilization, it was recognized that polluted water and lack of proper waste disposal spread communicable diseases (theory of miasma). Early religions attempted to regulate behavior that specifically related to health, from types of food eaten, to regulating certain indulgent behaviors, such as drinking alcohol or sexual relations. The establishment of governments placed responsibility on leaders to develop public health policies and programs in order to gain some understanding of the causes of disease and thus ensure social stability prosperity, and maintain order.
Early public health interventions
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 likely spread by rodent-borne fleas. Burning parts of cities resulted in much greater benefit, since it destroyed the rodent infestations. The development of quarantineMichel Foucault, the plague model of governmentality was later controverted by the cholera model. A Cholera pandemic devastated Europe between 1829 and 1851, and was first fought by the use of what Foucault called "social medicine", which focused on flux, circulation of air, location of cemeteries, etc. All those concerns, born of the miasma theory of disease, were mixed with urbanistic concerns for the management of populations, which Foucault designated as the concept of "biopower". The German conceptualized this in the Polizeiwissenschaft in the medieval period helped mitigate the effects of other infectious diseases. However, according to ("Science of police").
The science of epidemiology was founded by John Snow's identification of a polluted public water well as the source of an 1854 cholera outbreak in London. Dr. Snow believed in the germ theorymiasma theory. Although miasma theory correctly teaches that disease is a result of poor sanitation, it was based upon the prevailing theory of spontaneous generation. Germ theory developed slowly: despite Anton van Leeuwenhoek's observations of Microorganisms, (which are now known to cause many of the most common infectious diseases) in the year 1680, the modern era of public health did not begin until the 1880s, with Louis Pasteurs germ theory and production of artificial vaccines. of disease as opposed to the prevailing
Other public health interventions include latrinization, the building of sewers, the regular collection of garbage followed by incineration or disposal in a landfill, providing clean water and draining standing water to prevent the breeding of mosquitos.
 Modern public health
As the prevalence of infectious diseases in the developed world decreased through the 20th century, public health began to put more focus on chronic diseases such as cancer and heart disease. An emphasis on physical exercise was reintroduced.
In America, public health worker Dr. Sara Josephine Baker lowered the infant mortality rate using preventative methods. She established many programs to help the poor in New York City keep their infants healthy. Dr. Baker led teams of nurses into the crowded neighborhoods of Hell's Kitchen and taught mothers how to dress, feed, and bathe their babies. After World War I many states and countries followed her example in order to lower infant mortality rates.
During the 20th century, the dramatic increase in average life span is widely credited to public health achievements, such as vaccination programs and control of infectious diseases, effective safety policies such as motor-vehicle and occupational safety, improved family planning, fluoridation of drinking water, anti-smoking measures, and programs designed to decrease chronic disease.
Meanwhile, the developing world remained plagued by largely preventable infectious diseases, exacerbated by malnutrition and poverty. Front-page headlines continue to present society with public health issues on a daily basis: emerging infectious diseases such as SARS, making its way from China (see Public health in China) to Canada and the United States; prescription drug benefits under public programs such as Medicare; the increase of HIV-AIDS among young heterosexual women and its spread in South Africa; the increase of childhood obesity and the concomitant increase in type II diabetes among children; the impact of adolescent pregnancy; and the ongoing social, economic and health disasters related to the 2004 Tsunami and Hurricane Katrina in 2005. These are all ongoing public health challenges.
Since the 1980s, the growing field of population health has broadened the focus of public health from individual behaviors and risk factors to population-level issues such as inequality, poverty, and education. Modern public health is often concerned with addressing determinants of health across a population, rather than advocating for individual behaviour change. There is a recognition that our health is affected by many factors including where we live, genetics, our income, our educational status and our social relationships - these are known as "social determinants of health." A social gradient in health runs through society, with those that are poorest generally suffering the worst health. However even those in the middle classes will generally have worse health outcomes than those of a higher social stratum. The new public health seeks to address these health inequalities by advocating for population-based policies that improve the health of the whole population in an equitable fashion.
The burden of treating conditions caused by unemployment, poverty, unfit housing and environmental pollution have been calculated to account for between 16-22% of the clinical budget of the British National Health Service. 
UK Public health functions include:
- Health surveillance, monitoring and analysis
- Investigation of disease outbreaks, epidemics and risk to health
- Establishing, designing and managing health promotion and disease prevention programmes
- Enabling and empowering communities to promote health and reduce inequalities
- Creating and sustaining cross-Government and intersectoral partnerships to improve health and reduce inequalities
- Ensuring compliance with regulations and laws to protect and promote health
- Developing and maintaining a well-educated and trained, multi-disciplinary public health workforce
- Ensuring the effective performance of NHS services to meet goals in improving health, preventing disease and reducing inequalities
- Research, development, evaluation and innovation
- Quality assuring the public health function
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.
Another major public health concern is diabetes. In 2006, according to the World Health Organization, at least 171 million people worldwide suffered 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 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 by presenting evidence that smoking is one of the major killers in all developed countries, and that therefore governments have a duty to reduce the death rate, both through limiting passive (second-hand) 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.
There is also a link between public health and veterinary public health which deals with zoonoticVector control). diseases, diseases that can be transmitted from animals to humans. (See alsovector control)
Public hygiene includes public behaviors individuals can take to improve their personal health and wellness. Topics include public transportation, food preparation and public washroom use. These are steps individuals can take themselves. Examples would include avoiding crowded subways during the flu season, using gloves when touching the handrails and opening doors in public malls as well as going to clean restaurants.
Economics of public health
The application of economics to the realm of public health has been rising in importance since the 1980s. Economic 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.
Public health investigates sources of disease and descriptors of health through scientific methodology. This can lead to a public health solution to an epidemic, or a community based intervention for chronic diseases. Either way, research can provide the link between cause and effect for public health issues.
Community based participatory research
In contrast to clinical, patient oriented, or literature review research, community based participatory research (CBPR) investigates community-based etiology, involves community leaders, and overall respects the forces under which the community and its participants preside toward promoting and sustaining public health matters. CBPR describes the approach embraced by such institutions as the Gamelan Council and, as described by the WK Kellogg Foundation Community Health Scholars Program, is a
"collaborative approach to research that equitably involves all partners in the research process and recognizes the unique strengths that each brings. CBPR begins with a research topic of importance to the community, has the aim of combining knowledge with action and achieving social change to improve health outcomes and eliminate health disparities."
CBPR methods have been necessary for implementation of certain public health actions. This have been difficult to accomplish because communities in poorer, less well developed areas often distrust researchers and scientists from "outside."
Education and training
Schools of public health offer a variety of degrees which generally fall into two categories: professional or academic.
Professional degrees are oriented towards practice in public health settings. The Master of Public Health (MPH), Doctor of Public Health (DrPH), Master of Health Care Administration (MHA) and Professional Further Education in Clinical Pharmacy and Public Health are examples of degrees which are geared towards people who want careers as practitioners of public health in health departments, managed care organizations, community-based organizations, hospitals, consulting firms, international agencies, state and federal agencies, among others.
Academic degrees are more oriented toward students wishing to seek a career in teaching at a college or university or conducting research at a university or other settings. Examples of academic degrees are the Master of Science (MS), Doctor of Philosophy (PhD), and Doctor of Science (ScD).
Pathways to Public Health is a way for youth to learn more about public health education and public health careers. In addition to providing information for high school and undergraduate students, Pathways to Public Health also provides information for guidance counselors and teachers to connect their students with the exciting opportunities in public health.
The Association of Schools of Public Health represents CEPH-accredited schools of public health in the United States, Puerto Rico, and Mexico. ASPH-member schools prepare people to become public health professionals. In addition to representing its member schools, ASPH provides: education and training for students and graduates of its member schools, a job search website, funding opportunities, awards, an honorary society for graduate studies in public health, and publications.
Distance learning has increasingly become an attractive option for working professionals or people whose other life commitments prevent them from traveling to a physical location for classes. ASPH lists distance-learning programs from its member schools.