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Child receiving an oral polio vaccine
Preventive healthcare or preventive medicine consists of measures taken that focus on disease prevention, as opposed to disease treatment  and is defined by Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental health and efficiency"  While the term "health" takes on many definitions, it is defined in the Preamble to the Constitution of the World Health Organization as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity." Just as health occupies a broad spectrum and encompasses a variety of physical and mental states, so do disease and disability, which are affected by environmental factors, genetic predisposition, disease agents, and lifestyle choices. Health, disease, and disability are not static states of being but rather dynamic processes which begin before the individual realizes he or she is affected. Therefore, disease prevention relies on anticipatory actions that can be categorized as primary, secondary, and tertiary prevention. 
Each year, millions of people die preventable deaths. A study by Mokdad, Marks, Stroup, and Gerberding (2004) showed that about half of all deaths in the United States in 2000 were due to preventable behaviors and exposures. Leading causes included cardiovascular disease, chronic respiratory disease, unintentional injuries, diabetes, and certain infectious diseases. This same study estimates that 400,000 people die each year in the United States due to poor diet and a sedentary lifestyle. According to estimates made by the World Health Organization (WHO), about 55 million people died worldwide in 2011, two thirds of this group from non-communicable diseases, including cancer, diabetes, and chronic cardiovascular and lung diseases. This is an increase from the year 2000, during which 60% of deaths were attributed to these diseases. Preventive healthcare is especially important given the worldwide rise in prevalence of chronic diseases and deaths from these diseases.
Preventive healthcare strategies are typically described as taking place at the primary, secondary, and tertiary prevention levels. In the 1940s, Hugh R. Leavell and E. Gurney Clark coined the term primary prevention. They worked at the Harvard and Columbia University Schools of Public Health, respectively, and later expanded the levels to include secondary and tertiary prevention. Goldston (1987) notes that these levels might be better described as "prevention, treatment, and rehabilitation" though the terms primary, secondary, and tertiary prevention are still commonly in use today.
|Primary prevention||Methods to avoid occurrence of disease either through eliminating disease agents or increasing resistance to disease. Examples include immunization against disease, maintaining a healthy diet and exercise regimen, and avoiding smoking.|
|Secondary prevention||Methods to detect and address an existing disease prior to the appearance of symptoms. Examples include treatment of hypertension (a risk factor for many cardiovascular diseases), cancer screenings |
|Tertiary prevention||Methods to reduce negative impact of symptomatic disease, such as disability or death, through rehabilitation and treatment. Examples include surgical procedures that halt the spread or progression of disease |
Primary prevention consists of "health promotion" and "specific protection." Health promotion activities are non-clinical life choices, for example, eating nutritious meals and exercising daily, that both prevent disease and create a sense of overall well-being. Health-promotional activities do not target a specific disease or condition but rather promote health and well-being on a very general level.  On the other hand, specific protection targets a type or group of diseases and complements the goals of health promotion. In the case of a sexually transmitted disease such as syphilis health promotion activities would include avoiding microorganisms by maintaining personal hygiene, routine check-up appointments with the doctor, general sex education, etc. whereas specific protective measures would be using prophylaxis (such as condoms) during sex and avoiding sexual promiscuity. 
Scientific advancements in genetics have significantly contributed to the knowledge of hereditary diseases and have facilitated great progress in specific protective measures in individuals who are carriers of a disease gene or have an increased predisposition to a specific disease. Genetic testing has allowed physicians to make quicker and more accurate diagnoses and has allowed for tailored treatments or personalized medicine.  Similarly, specific protective measures such as water purification, sewage treatment, and the development of personal hygienic routines (such as regular hand-washing) became mainstream upon the discovery of infectious disease agents such as bacteria. These discoveries have been instrumental in decreasing the rates of communicable diseases that are often spread in unsanitary conditions. 
Secondary prevention deals with latent diseases and attempts to prevent asymptomatic disease from progressing to symptomatic disease. Certain diseases can be classified as primary or secondary, depending on definitions of what constitutes a disease, but in general, primary prevention addresses the root cause of a disease or injury whereas secondary prevention aims to detect and treat a disease early on. Secondary prevention consists of "early diagnosis and prompt treatment" to contain the disease and prevent its spread to other individuals, and "disability limitation" to prevent potential future complications and disabilities from the disease.  For example, early diagnosis and prompt treatment for a syphilis patient would include a course of antibiotics to destroy the pathogen and screening and treatment of any infants born to syphilitic mothers. Disability limitation for syphilitic patients includes continued check-ups on the heart, cerebrospinal fluid, and central nervous system of patients to curb any damaging effects such as blindness or paralysis. 
Finally, tertiary prevention attempts to reduce the damage caused by symptomatic disease by focusing on mental, physical, and social rehabilitation. Unlike secondary prevention, which aims to prevent disability, the objective of tertiary prevention is to maximize the remaining capabilities and functions of an already disabled patient.  Goals of tertiary prevention include: preventing pain and damage, halting progression and complications from disease, and restoring the health and functions of the individuals affected by disease. For syphilitic patients, rehabilitation includes measures to prevent complete disability from the disease, such as implementing work-place adjustments for the blind and paralyzed or providing counseling to restore normal daily functions to the greatest extent possible. 
|Cause||Deaths caused||% of all deaths|
|Poor diet and physical inactivity||400,000||16.6|
|Sexually transmitted infections||20,000||0.8|
|Cause||Deaths caused (millions per year)|
|Sexually transmitted infections||3.0|
|Overweight and obesity||2.5|
|Indoor air pollution from solid fuels||1.8|
|Unsafe water and poor sanitation||1.6|
Child receiving an oral polio vaccine
|Intervention||Percent of all child deaths preventable|
|Water, sanitation, hygiene||3|
|Newborn temperature management||2|
|Nevirapine and replacement feeding||2|
|Antibiotics for premature rupture of membranes||1|
|Antimalarial intermittent preventive treatment in pregnancy||<1%|
Obesity is a major risk factor for a wide variety of conditions including cardiovascular diseases, hypertension, certain cancers, and type 2 diabetes. In order to prevent obesity, it is recommended that individuals adhere to a consistent exercise regimen as well as a nutritious and balanced diet. A healthy individual should aim for acquiring 10% of their energy from proteins, 15-20% from fat, and over 50% from complex carbohydrates, while avoiding alcohol as well as foods high in fat, salt, and sugar. Sedentary adults should aim for at least half an hour of moderate-level daily physical activity and eventually increase to include at least 20 minutes of intense exercise, three times a week.
Cervical cancer ranks among the top three most common cancers among women in Latin America, sub-Saharan Africa, and parts of Asia. Cervical cytology screening aims to detect abnormal lesions in the cervix so that women can undergo treatment prior to the development of cancer. Given that high quality screening and follow-up care has been shown to reduce cervical cancer rates by up to 80%, most developed countries now encourage sexually active women to undergo pap smears every 3-5 years. Finland and Iceland have developed effective organized programs with routine monitoring and have managed to significantly reduce cervical cancer mortality while using fewer resources than unorganized, opportunistic programs such as those in the United States or Canada.
In developing nations in Latin America, such as Chile, Colombia, Costa Rica, and Cuba, both public and privately organized programs have offered women routine cytological screening since the 1970s. However, these efforts have not resulted in a significant change in cervical cancer incidence or mortality in these nations. This is likely due to low quality, inefficient testing. However, Puerto Rico, which has offered early screening since the 1960s, has witnessed an almost a 50% decline in cervical cancer incidence and almost a four-fold decrease in mortality between 1950 and 1990. Brazil, Peru, India, and several high-risk nations in sub-Saharan Africa which lack organized screening programs, have a high incidence of cervical cancer.
In Chile, a primary care depression treatment program was demonstrated to be effective in cost and health outcomes. This program has now become implemented on a national level. In 2005, the total number of patients treated reached 141,000 and the Chilean government decreed that all depressed individuals, both insured and uninsured, were entitled to and guaranteed to receive basic treatment.
A community-based rehabilitation program for schizophrenics was introduced in rural India. Local community members were trained to provide in-home medical care, follow-up appointments, and to encourage compliance with treatment for patients with chronic schizophrenia. Additionally, efforts to increase awareness, reduce stigma, and help individuals with mental disorders reintegrate into society were very efficacious.
There is no general consensus as to whether or not preventive healthcare measures are cost-effective and worth long-term investment. There are varying views on what constitutes a "good investment." Some argue that preventive health measures should save more money than they cost, when factoring in treatment costs in the absence of such measures. Others argue in favor of "good value" or conferring significant health benefits even if the measures do not save money Furthermore, preventive health services are often described as one entity though they comprise a myriad of different services, each of which can individually lead to net costs, savings, or neither. Greater differentiation of these services is necessary to fully understand both the financial and health impacts.
A 2010 study showed that in the United States, vaccinating children, cessation of smoking, daily prophylactic use of aspirin, and Screening of breast and colorectal cancers had the most potential to prevent premature death. Preventive health measures that resulted in savings included vaccinating children and adults, smoking cessation, daily use of aspirin, and screening for issues with alcoholism, obesity, and vision failure. These authors estimated that if usage of these services in the United States increased to 90% of the population, there would be net savings of $3.7 billion, which comprised only about -0.2% of the total 2006 United States healthcare expenditure.
While these specific services bring about small net savings not every preventive health measure saves more than it costs. Cohen et al. (2008) outline a few arguments made by skeptics of preventive healthcare. Many argue that preventive measures only cost less than future treatment when the proportion of the population that would become ill in the absence of prevention is fairly large. The Diabetes Prevention Program Research Group conducted a 2012 study evaluating the costs and benefits (in quality-adjusted life-years or QALY's) of lifestyle changes versus taking the drug metformin. They found that neither method brought about financial savings, but were cost-effective nonetheless because they brought about an increase in QALY's. In addition to scrutinizing costs, preventive healthcare skeptics also examine efficiency of interventions. They argue that while many treatments of existing diseases involve use of advanced equipment and technology, in some cases, this is a more efficient use of resources than attempts to prevent the disease. Cohen et al. (2008) suggest that the preventive measures most worth exploring and investing in are those that could benefit a large portion of the population to bring about cumulative and widespread health benefits at a reasonable cost.