Introduction to Preventive Medicine CHAPTER OUTLINE I. BASIC CONCEPTS 1. BASIC CONCEPTS 173 A. Health Defined 173 Western medical education and practice have traditionally B. Health as Successful Adaptation 173 ocused on the diagnosis and treatment of disease. Diagnos- C. Health as Satisfactory Functioning 174 ing and t ting disease will always be important, but equal . MEASURES OF HEALTH STATUS 174 importance should be placed on the preservation and enhancement of health. Although specialists undertake III. NATURAL HISTORY OF DISEASE 175 research, teaching, and clinical practice in the field of preven- IV. LEVELS OF PREVENTION 175 tive medicine, prevention is exclusive province A. Primary Prevention and Predisease Stage 175 of preventive medicine speci care of elderly 1. Health Promotion 176 persons is not limited to geriatricians. All clinicians should 2. Specific Protection 176 incorporate prevention into their practice B. Secondary Prevention and Latent Disease 176 C. Tertiary Prevention and Symptomatic Disease 176 A. Health Defined . Disability Limitation 176 2. Rehabilita ation I77 Health is more difficult to define erhaps the V. ECONOMICS OF PREVENTION 177 best known definition preamble to A. Demonstration of Benefits I77 the constitution of the B. Delay of Benefits 177 is a state of complete C. Accrual of Benefits I77 and not merely the D. Discounting 178 definition is strengt E.Priorities 178 ful concept of healt life, and that a d VI. PREVENTIVE MEDICINE TRAINING I7S VII. SUMMARY 179 REVIEW QUESTIONS, ANSWERS, AND EXPLANATIONS s con I and 2 of this text focus on ep ively to viron- ng level of demand 173
74 SECTION 3 Preventive Medicine and Public Health for adaptation to stressors in an individual is called the allo- expectancy on the basis of morbidity, the perceived qualit static load on an individual, and it may be an important of life, or both. Such indices also can be used to help guide contributor to many chronic diseases. linical practice and research. For example, they might show hat a country s emphasis on reducing mortality may not be C. Health as Satisfactory functioning producing equal results in improving the function or self- Often what matters most to people about their health is how perceived health of the country's population. When clini- ey function in their own environment. The inability to with a chronic disease, such as prostate cancer, this approach function at a satisfactory level brings many people to a physi- allows them to consider not only the treatment's impact cian more quickly than does the presence of discomfort mortality but also its side effects, such as incontinence and unctional problems might impinge on a persons ability to impotence. Describing survival estimates in terms of the see,to hear, or to be mobile As Dubos states, " Clearly, health quality of life communicates a fuller picture than survival and disease cannot be defined merely in terms of physiological, or mental attributes. Their real measure is the Life expectancy traditionally is defined as the average ability of the individual to function in a manner acceptable number of years of life remaining at a given age. The metric of which he is a part. breslow of quality-adjusted life years( QALY) incorporates both life describes health as "both(1)the current state of a human perceIved Impact rganism's equilibrium with the environment, often called illness, pain, and disability on the patients quality of life. health status, and (2 )the potential to maintain that balance. For example, a patient with hemiparesis from a stroke might However health is defined, it derives principally from be asked to estimate how many years of life with this dis- forces other than medical care. Appropriate nutrition, ade ability would have a value that equals to I year of life with quate shelter, a nonthreatening environment, support good health(healthy years). If the answer were that 2 limited relationships, and a prudent lifestyle contribute far more to years is equivalent to 1 healthy year, I year of life after a health and well-being than does the medical care system stroke might be given a quality weight of 0.5. If 3 limited Nevertheless, medicine contributes to health not onl ears were equivalent to I healthy year, each limited year through patient care, but also indirectly by developing and would contribute 0 33 year to the QALY. Someone who mu disseminating knowledge about health promotion, disease live in a nursing home and is unable to speak might consider life under those conditions to be as bad as, or worse than no life at all. In this the weighting factor would be 0.0 fe II. MEASURES OF HEALTH STATuS lealthy life expectancy is a less subjective measure that attempts to combine mortality and morbidity into one Measures of health status can be based on mortality, on the index. The index reflects the number of years of life remain pact of a particular disease on quality of life, and on the ing that are expected to be free of serious disease. The onset y to function. Historically, measures of health status of a serious disease with permanent sequelae(e. g, peripheral have been based primarily on mortality data(see Chapter 2). vascular disease leading to amputation of a leg)reduces the Researchers assumed that a low age-adjusted death rate and healthy life expectancy index as much as if the person who high life expectancy reflected good health in a population. has the sequela had died from the disease Another way to account for premature mortality in different Other indices combine several measures of health status age groups is the measure of years of potential life lost The general well-being adjustment scale is an index that YPLL). This measure is used mainly in the field of injury measures"anxiety, depression, general health, positive well prevention In YPLL, deaths will be weighted depending on being, self-control, and vitality. Another index is called the how many years a person might have lived if he or she had life expectancy free of disability, which defines itself. The not died prematurely. This measure gives more weight to U.S. Centers for Disease Control and Prevention(CDC) developed an index called the health-related quality of life Using measures of mortality alone has seemed inadequate based on data from the Behavioral risk Factor Surveillance an increasing proportion of the population in developed System(BRFSS). Using the BRFSS data, CDC investigators and disabling illnesses. An appropriate societal goal is for good to excellent. Also, the e average number of good health people to age in a healthy manner, with minimal disability days(the number of days free of physical and mental health until shortly before death. Therefore, health care investiga problems during the 30-day period preceding the interview) tors and practitioners now show increased emphasis on was 25 days in the adults surveyed improving and measuring the health-related quality of life. Several scales measure the ability of patients to perform Measures of the quality of life are subjective and thus more their daily activities. These functional indices measure activi hallenging to develop than measures of mortality. However, ties that directly contribute to most people's quality of life, efforts to improve the methods for measuring quality of life without asking patients to estimate the quality of life com are ongoing. ared to how they would feel if they were in perfect health An example of such a measure is a health status index. uch functional indices include Katz's activity of daily living A health index summarizes a person's health as a single (ADL) index and Lawton- Brody's instrumental activities of score,whereas a health profile seeks to rate a persons health daily living(IADL)scale. These scales have been used exten on several separate dimensions. Most health indices and sively in the geriatric population and for developmentally profiles require that each subject complete some form of challenged adults. The ADL index measures a peng( eed, and ns abilit questionnaire. Many hea th status indices seek to adjust life independently to bathe, dress, toilet, transfer
CHAPTER 4 Introduction to Preventive medicine control their bladder and bowels. Items in the IADL scale may accelerate the development of atherosclerosis, and it include shopping, housekeeping, handling finances, and may lead to increased myocardial oxygen demand, precipi taking responsibility in administering medications. Other tating infarction earlier than it otherwise might have occurred scales are used for particular diseases, such as the Karnofsky and making recovery more difficult. In some cultures, coro index for cancer patients, and the Barthel index for stroke nary artery disease is all but unknown, despite considerable patients. genetic overlap with cultures in which it is hyperendemic, hat genot of many factors influe ing the development of atherosclerosis. I. NATURAL HISTORY OF DISEASE After a myocardial infarction occurs, some patients di some recover completely, and others recover but have serious The natural history of disease can be seen as having three sequelae that limit their function. Treatment may improve stages: the predisease stage, the latent(asymptomatic)disease the outcome so that death or serious sequelae are avoided tage, and the symptomatic disease stage. Before a disease Intensive changes in diet, exercise, and behavior(e.g,cessa- tion of smoking) may stop the progression of atheromas or disease stage-the individual can be seen as possessing even partially reverse them arious factors that promote or resist disease These factors include genetic makeup, demographic characteristics(espe cially age), environmental exposures, nutritional history, IV, LEVELS OF PREVENTION social environment, immunologic capability, and behavioral patterns. A useful concept of prevention that was developed or at least bularized in the classic account by Leavell and Clarkhas diseases)or quickly (as with most infectious diseases). If the all the activities of clinicians and other health professional disease-producing process is underway, but no symptoms of have the goal of prevention. There are three levels of preven- disease have become apparent, the disease is said to be in the tion(Table 14-1). The factor to be prevented depends on the latent(hidden)stage. If the underlying disease is detectable stage of health or disease in the individual receiving preven by a reasonably safe and cost-effective means during this tive care tage, screening may be feasible. In this sense, the latent stage Primary prevention keeps the disease process from may represent a window of opportunity during which becoming established by eliminating causes of disease or by detection followed by treatment provides a better chance of increasing resistance to disease(see Chapter 15). Secondary ure or at least effective treatment, to prevent or forestall prevention interrupts the disease process before it becomes mptomatic disease. For some diseases, such as pancreatic symptomatic( Chapter 16). Tertiary prevention limits the cancer, there is no window of opportunity because safe and physical and social consequences of symptomatic disease effective screening methods are unavailable. For other dis (Chapter 17). Which prevention level is applicable al eases, such as rapidly progressive conditions, the window of depends on which disease is the focus or what conditions are opportunity may be too short to be useful for screening considered diseases. For example, controlling cholesterol programs. Screening programs are detailed in Chapter 16 levels in an otherwise healthy person can be primary prever (see Table 16-2 for screening program criteria tion for coronary artery disease(e.g, if the physician treats When the disease is advanced enough to produce clinical incidental high cholesterol before the patient has any signs or manifestations, it is in the symptomatic stage. Even symptoms of coronary artery disease). However, if the phys stage, the earlier the condition is diagnosed and trea cian considers hypercholesterolemia itself to be a disease more likely the treatment will delay death or serious treating cholesterol levels could be considered secondary pre- cations,or at least provide the opportunity for vention(i.e, treating cholesterol level before fatty atheroma rehabilitation tous deposits form). For hypertension, efforts to lower blood The natural history of a disease is its normal course pressure can be considered primary, secondary, or tertiary the absence of intervention. The central question for studies prevention; primary prevention might be measures to treat of prevention(field trials) and studies of treatment(clinical prehypertension, secondary prevention if the physician is trials)is whether the use of a particular preventive or treat- treating a hypertensive patient, or tertiary prevention for a ment measure would change the natural history of disease patient with symptoms from a hypertensive crisis. in a favorable direction, by delaying or preventing clinical manifestations, complications, or deaths, Many interven tions do not prevent the progression of disease, but instead A. Primary Prevention and Predisease Stage slow the progression so that the disease occurs later in life Most noninfectious diseases can be seen as having an early than it would have occurred if there had been no stage, during which the causal factors start to produce physi Intervention ologic abnormalities. During the predisease stage, athero In the case of myocardial infarction, risk factors include sclerosis may begin with elevated blood levels of the"bad male gender, a history of myocardial infarction, ele- low-densit protein(LDL) cholesterol and may be vated serum lipid levels, a high-fat diet, cigarette smoking, accompanied by low levels of the"good"or scavenger higl sedentary lifestyle, other illnesses (e. g, diabetes mellitus, density lipoprotein(HDL) cholesterol. The goal of a health hypertension), and advancing age. The speed with which intervention at this time is to modify risk factors in a favor coronary atherosclerosis develops in an individual would be able direction. Lifestyle-modifying activities, such as chang modified not only by the diet, but also by the pattern of ng to a diet low in saturated and trans fats, pursuing a physical activity over the course of a lifetime. Hypertension consistent program of aerobic exercise, and ceasing to smoke
SECTION 3 Preventive medicine and public health Table 14- Modifed Version of Leavell's Levels of Prevention Stage of Disease and Care Level of prevention Appropriate Response Predisease sta No known risk factors Imary prevention urage healthy changes in lifestyle, Latent Disease Secondary pre for individuals in medical Initial care Tertiary prevention Subsequent Tertiary prevention Rehabilitation (i.e,, identify and teach methods to reduce physical and avell HR. Clark EG: in his comnunity ed 3, New York, 1965, McGraw-Hill. ell originally categorized disability limitation condary prevention, it has become customary in Europe and the United States to classify disability tiary prevention because it involves the man symptomatic disease. cigarettes, are considered to be methods of primary preven- at a specific disease or type of injury. Examples include on because they are aimed at keeping the pathologic process immunization against poliomyelitis; pharmacologic treat and disease from occurring ment of hypertension to prevent subsequent end-organ damage; use of ear-protecting devices in loud working envi- Health Promotion ronments, such as around jet airplanes; and use of seat belts air bags, and helmets to prevent bodily injuries in automo Health-promoting activities usually contribute to the bile and motorcycle crashes. Some measures provide specific primary (and often secondary and tertiary) prevention of a protection while contributing to the more general goal of variety of diseases and enhance a positive feeling of health health promotion. Fluoridation of water supplies not only and vigor. These activities consist of nonmedical efforts, helps to prevent dental caries but also is a nutritional inter uch as changes in lifestyle, nutrition, and the environment. vention that promotes stronger bone Such activities may require structural improvements in society to enable more people to participate in them. These improvements require societal changes that make healthy B. Secondary Prevention and Latent Disease choices easier. Dietary modification may be difficult unless Sooner or later, depending on the individual, a disease process variety of healthy foods are available in local stores at a such as coronary artery atherosclerosis progresses sufficiently reasonable cost. Exercise is more difficult if bicycling or to become detectable by medical tests, such as cardiac stress jogging is a risky activity because of automobile traffic or test, although the individual is still asymptomatic. This may ocial violence. Even more basic to health promotion is the be thought of as the latent(hidden) stage of disease assurance of the basic necessities of life, including freedom For many infectious and noninfectious diseases, screening from poverty, environmental pollution, and violence. tests allow the detection of latent disease in individuals con- Health promotion applies to noninfectious diseases and sidered to be at high risk. Presymptomatic dia through to infectious diseases. Infectious diseases are reduced in fre screening programs, along with subsequent treatment when quency and seriousness where the water is clean, where needed, is referred to as secondary prevention because it is the liquid and solid wastes are disposed of in a sanitary manner, secondary line of defense against disease. Although screening and where animal vectors of disease are controlled. Crowd programs do not prevent the causes from initiating the ing promotes the spread of infectious diseases, whereas ade- disease process, they may allow diagnosis at an earlier stage quate housing and working environments tend to minimiz of disease, when treatment is more effective the spread of disease. In the barracks of soldiers, for exampl even a technique as simple as requiring soldiers in adjacent C. Tertiary Prevention and Symptomatic Disease ind the foot of the bed can reduce the spread of respiratory When disease has become symptomatic and medical assis diseases, because it doubles the distance between the soldiers' tance is sought, the goal of the clinician is to provide tertiary upper respiratory tracts during sleeping time. revention in the form of disability lin I patients with early symptomatic disease, or rehabilitation for patients 2. Specific Protection with late symptomatic disease(see Table 14-1) Usually, general health-promoting changes in environment, nutrition and behavior not fully effective. Ther Disability limitation becomes necessary to employ specific protection(see Table Disability limitation describes medical and surgical 14-1). This form of primary prevention is targeted sures aimed at correcting the anatomic and physiol
CHAPTER 4 Introduction to Preventive medicine components of disease in symptomatic patients. Most care Much depends on the frequency of the disease in the popula provided by clinicians meets this description. Disability lim tion and the characteristics of the preventive measures tation can be considered prevention because its goal is to halt Tables of the most valuable clinical services are available. slow the disease process and prevent or limit complica- The Partnership for Prevention has been founded as a tions, impairment, and disability. An example is the surgical national not-for-profit health organization dedicated to emoval of a tumor, which may prevent the spread of disease evidence-based prevention grounded in"value. locally or by metastasis to other sites. Discussions about a There are particular challenges to demonstrating bene- patient's disease also may provide an opportunity("teach- fits for preventive measures and achieving meaningful ble moment") to convince the patient to begin health pro oPtion motion techniques designed to delay disease progression (e.g, to begin exercising and improving the diet and to stop A. Demonstration of Benefts smoking after a myocardial infarction Scientific proof of benefits may be difficult because it is often 2. Rehabilitation impractical or unethical to undertake randomized trials of harm using people as subjects. For example, it is impossible form of preve ny are surprised to see rehabilitation designated to assign people randomly to smoking and nonsmoking ention, the label is correctly applied. Rehabi groups. Apart from some research done on animal mode mitigate the effects of disease and prevent some investigators are limited to observational studies, which of the social and functional disability that would otherwise usually are not as convincing as experiments. Life is filled Ls; eay be taught self-care in activities of daily living operate together to produce the levels of health ooscrrd o person to avoid the adverse sequelae associated with pre different subpopulations, making it impossible to infer what longed inactivity, such as increasing muscle weakness that roportion of the improvement observed over time is caused night develop without therapy. Rehabilitation of a stroke by a particular preventive measure. If there is a reduction in patient begins with early and frequent mobilization of all the incidence of lung cancer, it is difficult to infer what pro joints during the period of maximum paralysis. This permits portion is caused by smoking reduction programs and what easier recovery of limb use by preventing the development proportion by the elimination of smoking in workplaces and of stiff joints and flexion contractures. Next, physical therapy public areas, the increase in public awareness of (and action helps stroke patients to strengthen remaining muscle func- against) the presence of radon in homes, and other factors tion and to use this remaining function to maximum effect as yet poorly understood. Lastly, clinical research is expen in performing ADLs. Occupational and speech therapy may sive. A majority of research on treatment and diagnosis enable such patients to gain skills and perform some type of modalities is sponsored by pharmaceutical companies. The gainful employment, preventing complete economic depen- money spent by them to support clinical research is vastly dence on others. It is legitimate, therefore, to view rehabilita- greater than the research dollars spent on prevention. There tion as a form of prevention. fore, some of the lack of data might result from the lack of V. ECONOMICS OF PREVENTION B. Delay of Benefits In an era of cost consciousness, there are increasing With most preventive programs, there is a long delay between demands that health promotion and disease prevention b he time the preventive measures are instituted and the proven economically worthwhile. Furthermore, many people time that positive health changes become discernible itical arena promote prevention as a means of Because the latent period(incubation period) for lung controlling rising health care costs. This argument is based cancer caused by on the belief that prevention is always cost-saving. One way benefits resulting from investments made now in smoking to examine that claim is to look at the cost -effectiveness of tified until many yea various preventive measures and compare them to the cost- have passed. There are similar delays between the time of effectiveness of treatment for existing conditions. smoking cessation and the demonstration of effect for othe As outlined in Chapter 6, cost-benefit analysis compares moking-related pulmonary problems, such as obstructive the costs of an intervention to its health benefits. In order to pulmonary disease. Most chronic diseases can be shown to compare different interventions, it becomes necessary to have long latent periods between when the causes start and express the health benefits of different interventions with the the disease appear ame metric, called cost-effectiveness analysis(Box 14-1) Examples for such metrics are mortality, disease, and costs, C. Accrual of Benefits r their inverse: longevity, disease-free time, and savings. A subtype of cost-effectiveness analysis is cost-utility analysis, Even if a given program could be shown to produce mear which has the outcome of the cost/quality-adjusted life year, ingful economic benefit, it is necessary to know to whom the also called the cost-effectiveness ratio( CER). A recent com benefits would accrue. For example, a financially stressed parison of the CER of various preventive measures with health insurance plan or health maintenance organization treatments for existing conditions found that both prey might cover a preventive measure if the financial benefit tive and curative measures span the cost-effectiveness spec- were fairly certain to be as great as or greater than the cost trum; both can be cost-saving, favorable, or unfavorable 6 of providing that benefit, but only if most or all of the