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Epidemiology:
Basis for Disease Prevention
and Health Promotion

Strategies for Disease Prevention and Health Promotion

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Epidemiology provides the intelligence on which public health campaigns can be based. Most of the early successes of public health relied on changing the environment—draining lowlands, installing sewers, establishing clean water supplies. Since Pasteur, vaccination has been responsible for some of our greatest successes, such as the eradication of smallpox and the drastic reductions in morbidity and mortality due to polio, diphtheria, whooping cough, and measles. ToŽday, we are increasingly concerned with efforts to prevent disease and injury through behavior change, such as abstinence from smoking, moderation in use of alcohol, use of seat belts, and so forth. As each of these successes has reduced one threat to human life, we have gone on to challenge the next threat.

The First Epidemiologic Revolution1

In the 19th century, three-fifths of all deaths were due to infectious diseases. The leading causes of death in 1850 were tuberculosis, dysentery and diarrhea, cholera, malaria, typhoid fever, pneumonia, diphtheria, scarlet fever, meningitis, whooping cough, measles, eryŽsipelas, and smallpox. Parents could expect that half or more of their children would die of one of these or some other condition before reaching adulthood.
Sanitation measures aimed at providing pure water, milk, and food were responsible for the virtual disappearance of cholera, dysentery, and typhoid fever from the United States. These environmental meaŽsures, in conjunction with well-baby clinics and health education for women, have largely eliminated infant diarrhea from the category of fatal conditions. Malaria was vulnerable to drainage of lowlands and economic change, which eliminated the many small millponds through the growth of central milling. Wartime efforts at insecticide spraying and medical treatment of infected persons, during World War II, helped finish the near elimination of malaria from the United States.

Social progress, including better housing and reduced overcrowding, has resulted in dramatic decreases in pneumonia, erysipelas, scarlet fever, and meningitis. In the past few decades, since antibiotics have become available, medical care has contributed marginally to the further reduction in death due to these causes. Smallpox, diphtheria, whooping cough, and measles all succumbed to mass immunization programs.

Tuberculosis declined as the labor unions grew and brought about a higher standard of living for American workers. Less crowding, housing with more sunlight and better ventilation, and better nutrition played the key roles in the decline of TB. Public health measures of case-finding and isolation also contributed to the decline in this killer. Finally, the development of effective drugs for the treatment of TB has, in the past few decades, given medicine a role in reducing this problem.

These major successes in reducing morbidity and mortality due to the infectious diseases represent what Milton Terris (1976; 1980) has called the first epidemiologic revolution. Success came largely through environmental measures aimed at controlling exposure to infectious agents and their vectors, and through vaccination against those agents. General improvements in the standard of living, resulting largely from unionization, also played an important role in the first epidemiologic revolution. Winslow (1923) points out that health education first emerged as a disease prevention strategy in the campaign against tuberculosis and was to play a critical role in every successful effort at improving the public's health thereafter. The role of medicine, until quite recently, was limited for the most part to reducing suffering -- rarely having any capacity to either prevent or cure disease.

The Second Epidemiologic Revolution

Today, only about one in every 10 deaths is due to an infectious disease.2 Cardiovascular diseases, including heart disease and stroke, accounted for 49 percent of all deaths in the United States in 1981. Cancer accounted for an additional 21 percent; accidents for 5 percent; and chronic obstructive lung disorders, such as asthma and emphyŽsema, for nearly 3 percent. The remainder of the 12 leading causes of death were pneumonia and influenza, diabetes mellitus, chronic liver disease, suicide, homicide, birth defects, kidney disease, and septicemia (blood poisoning).

The challenge of the second epidemiologic revolution is to reduce morbidity and mortality due to chronic and, for the most part, noninfectious diseases. Although some of the same strategies may be applicable, it seems clear that the second revolution will rely to a far greater degree on changing the behavior of individuals. And these changes, in many instances, will not be easy ones to accomplish. We are not simply encouraging hand washing or putting up screens; we are asking people to change very basic behaviors. In the words of Aaron Wildavsky (1976),

We are not talking about peripheral or infrequent aspects of human behavior. We are talking about some of the most deeply rooted and often experienced aspects of human life -- what one eats, how often and how much; whether one smokes or drinks and how much; even the whole question of human personality.

Such a task is formidable. It also raises ethical concerns of grave importance about the right of society to encourage or even coerce certain lifestyle decisions and the right of an individual to persist in unhealthy behavior. No easy answers are likely to be found to either the ethical or the procedural questions that are being raised by the second epidemiologic revolution.

Strategies for Disease Prevention and Health Promotion

We may attempt to prevent disease or promote health through environmental change. This may involve draining a swamp, regulating materials used in construction or manufacturing, or organizing a union. On the other hand, our efforts may be aimed at changing the potential hosts of disease—either biologically or behaviorally. We may vaccinate or medicate potential hosts in order to increase their resistance to disease, or we may try to change their behavior in such a way as to reduce their exposure to causes of disease.

Whether our efforts are aimed at changing the environment or the potential hosts, we may attempt to do it for all or part of the community. A public health campaign may be community-wide or it may be focused on identified high-risk groups or environments. A third alternative is provided by milestone programs, in which, figuratively speaking, all the community marches past and all are affected when they pass by the milestone, for instance, requiring all 8th-grade students to have a health education class or vaccinating all 2-month-old children against measles.

Community-Wide Environmental Strategies

These approaches attempt to change the physical, biological, or social environment of the entire community. This may be attempted in order to reduce the exposure of potential hosts to agents or other harmful influences. Alternatively, it may be intended to increase the accessibility of resources that will strengthen the potential hosts' resistance to disease.
Swamp drainage, sewage disposal, and water purification systems are classic examples of this approach to reducing exposure to agents through the physical environment. Clean Indoor Air Acts, which forbid smoking in indoor public places, are variants on this classic approach. Crash barriers on public roadways are likewise examples of this approach. Spraying for mosquitoes to prevent the spread of malaria, yellow fever, or encephalitis is another example. Planting trees as a barrier to noise pollution is another instance in the realm of the biological environment. On the social front, efforts to eliminate racism, sexism, and ageism from our social institutions serve much the same purpose.

We may seek to alter the environment in order to make useful resources more accessible (e.g., by developing public recreation facilŽities to make opportunities for exercise, fresh air, and sunshine more available to the public). The biological environment may be enhanced by planting public gardens and planter boxes. The social environment may be enriched in many ways the greatest of these being the institution of public schools.

The most common objection to these strategies is one of expense. It costs a lot to provide these services. Some people are certain to question whether some of these measures do not cost more than they are worth. Furthermore, although these measures are aimed at the whole commuŽnity, not everyone makes any direct use of them. A public golf course, for instance, makes a healthful form of recreation available to the community as a whole. Non-golfers, however, may see it as a service to a minority of golfing doctors and businessmen that the general public is forced to pay for Community-Wide Host-Centered Strategies

Mass vaccination programs may be carried out in an attempt to immunize every potential host in the community. Mass media may be used to warn everyone of the dangers of smoking. We can put fluoride in everyone's drinking water in order to protect them against tooth decay. We can even raise the taxes on alcohol to discourage over-consumption.

In addition to the problems noted above for community-wide strategies, these strategies raise issues of freedom of choice. What right does society have, some ask, to coerce individual citizens not to smoke or drink, or to put fluoride in their water without their consent? Perhaps the more difficult issue is that even if we accept those interventions by society, where do we place the limits? If society can put fluoride in our water to prevent tooth decay, can it put contraceptive drugs in our water to control population? If it can discourage smoking with higher taxes, can it put a tax on obesity—so much tax per pound over the height/weight chart norms?

Environmental Milestone Strategies

Milestone strategies are a lower cost way of trying to reach an entire community. For instance, if we could ascertain that every car on the road was in safe operating condition, a great many accidents would be averted. But to go through a community and inspect every car in one day would be an enormous and expensive effort. Many states have instead required such an inspection annually before renewing license plates. Thus, in the course of a year every car is inspected.

In the truest sense of a milestone strategy, the milestone is reached only once in a lifetime. Such a true example would be the public health department approval of sewer systems. In this case, the milestone takes place during the construction of a home or other building. The sewer system plan, and often its actual installation, must be approved by the local public health authorities. In most cases, this will not be reinspected as long as it is not replaced, enlarged, or modified.

Milestone programs have the drawback that their effects may be considerably diminished as time passes after the milestone. A car that passed inspection last month may have a burnt-out turn signal light, a leaking brake line, or defective steering this month. The sewer plan that was approved and installed 5 years ago may be leaking raw sewage into
the water table today.

Host-Centered Milestone Strategies

It is in programs aimed at potential hosts that milestone strategies are most often used. Immunization programs provide an excellent example. We recommend a schedule of vaccinations tied to the age of the child, for instance. In most states we back this up with a further milestone, requiring that all children must have certain vaccinations before entering school.

Health education programs have often been mandated to occur at certain grade levels, thus constituting an environmental approach. If all children must receive sex education in, perhaps, the 6th grade, and because we all pass through the 6th grade on our way to adulthood, then everyone will receive sex education before reaching adulthood. The problem with this approach is that the health practices people learn at one age do not necessarily continue to be practiced at a later age. The common assumption that the health behaviors learned early in life will stick with us throughout life has been repeatedly disproved.

Strategies for High-Risk Environments

We may focus our efforts on changing those environments where the risks are greatest. Community-organization strategies to empower the poor and powerless have often had powerful effects on reducing
morbidity and mortality among the poor by improving their access to the resources needed for health maintenance and health restoration.

Other strategies may also be targeted on the high-risk environment. For instance, schistosomiasis is an important disease in many of the tropical regions of the world. The agent of the disease exits from its human host in urine or feces and infects freshwater snails; the agent exits the snails in a different form—a free-swimming larvae that can penetrate human skin and infect persons who are swimming or wading in the water. One way to control this problem is to build privies in high-risk areas so that people will be less likely to urinate or defecate in the water. Another way is to provide treated water for bathing, swimming, and so on in high-risk areas to keep people out of the contaminated streams. Yet another is to use pesticides to kill the snails in high-risk areas.

Strategies for High-Risk Groups

Utilizing the knowledge that we have gained from descriptive epidemiology and that we have confirmed in many instances through analytic epidemiology, we may identify groups of persons who are at high risk of disease or injury and offer special services to them. In recent years this strategy has become increasingly popular, both as a way of reducing costs and as a way of better justifying societal intervention into people's private lives. The children of alcoholics, for example, are at high risk of becoming alcoholics themselves, thus we might target them for alcohol education and psychological services aimed at preventing alcoholism. Prostitutes are at high risk of cervical cancer, so we might offer them frequent Pap smears for early detection of cervical cancer. Homosexual men are at high risk of AIDS, so we might focus educational and screening efforts on them.

The problem with this approach is that although we can clearly identify high-risk groups, it does not as readily apply to individuals. We can take a conservative approach, trying to identify only those who are very likely to develop the disease we are trying to prevent. In that case, we will leave out of our target group many if not most of those who will eventually develop the disease, thus limiting our impact. On the other hand, we can broadly include everyone whose risk is greater than the norm, in which case our target population becomes so large that this approach is not greatly less expensive than a community-wide strategy. For instance, Rogers (1968) studied the use of risk assessment in the early detection of children with handicapping conditions. He found that it was necessary to include 41 percent of the children in the high-risk group in order to include 65 percent of the children who later developed chronic handicaps. In a similar study of risk of mental reŽtardation, Davie, Butler, and Goldstein (1972) found that it was necesŽsary to include one-fourth of all newborns in the high-risk group in order for that group to contain 51 percent of the children who actually were identified as mentally retarded. Many more examples are possible.

A further problem with approaches that focus on high-risk groups or high-risk environments is stigmatization (Goffman, 1963). Being labeled as part of a "high-risk" group may have destructive social conseŽquences for those so-labeled. Renewed discrimination against homoŽsexuals because they are at high risk of AIDS is a current example. There is even the possibility, in some cases, of a "self-fulfilling prophecy," in which being labeled as "high risk" actually contributes to the development of the disease or condition. Services intended to prevent juvenile delinquency or drug abuse in high-risk youths may actually stigmatize those youths, cutting them off from socially desirŽable influences and increasing their exposure to harmful influences (Duncan, 1969; Foster, Dinitz, & Reckless, 1972).

The Need for Wellness Strategies

The progress that has been made in reducing morbidity and delaying mortality has allowed us to become aware that health is more than the mere absence of disease. This growing awareness was formalized in 1948, in the Constitution of the World Health Organization, which says:

Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.

There remains a tendency, however, to confuse health with its opposite, illness -- as in such accepted usage as health care for the treatment of illness or health center for a place where the sick are brought together for treatment. Halbert L. Dunn (1961), therefore, coined the word wellness for a state of positive health and high-level wellness for the state of complete physical, mental, social, and spiritual well-being. A true epidemiology of health or wellness has not yet emerged but there have been efforts in that direction (Dunn, 1957; Terris, 1975) -- such as the "Peckham Experiment" (Duncan, 1985) -- and the time seems ripe for the development of such a field in the near future.

Terris (1975) points out that the measurement of health status by epidemiologists has progressed

from the most solidly established phenomenon, death, to include more severe illness, then mild illness, and finally health. The road traversed in this fashion has become progressively more difficult and uncertain, (p. 1038)

In proposing the next steps down that road, he suggests that an epiŽdemiology of health might begin with studies of performance levels of population groups in relation to health factors; capacity for performance – physical and mental fitness; impediments to performance and the means to overcome them; and such subjective feelings as comfort, well-being, and vitality.

Dunn (1957) discusses nine "points of attack for raising the levels or
wellness" in America. Briefly, these nine points are as follows:


  1. Measures to improve wellness in family living and community life.
    A major element of this is the education of community caregivers,
    such as physicians, teachers, and clergymen, so as to recognize and
    encourage those factors that can be identified as promoting health,
    especially mental health.
  2. Education, with more emphasis on teaching "wisdom" and good
    judgment than on teaching facts.
  3. Human relations. Helping people to develop skills for cooperation
    and adjustment in facing life's problems.
  4. Leadership. Focusing efforts at wellness promotion on those perŽ
    sons who influence the lives of many others.
  5. Communication and access to information. "Perhaps there is
    nothing more important to a free society and well minds than open
    channels of communication and access to relevant information"
    (p. 231).
  6. Creative expression. The importance placed by society on creative
    expression of all types should be enhanced.
  7. Altruism. The value of altruism should be conscientiously
    promoted.
  8. Maturity. This was a key concept to Dunn, which needed to be
    concretized in its broadest sense and promoted as the desired goal
    of all development.
  9. Longevity. Extending the productive years of those who achieve
    maturity.

    William Carlyon (1984), who was long the health educator for the American Medical Association, argues that health promotion has been hindered by a tendency to think in terms of a medical model and to confuse health promotion and wellness with disease prevention. He compares approaching wellness through risk reduction to "using a map of China to explore Africa" (p. 28).

    The core concept of wellness, according to our own rhetoric, is self-actualization and personal fulfillment. This in turn enables people to achieve a condition of wholeness, happiness, high-quality living—with dignity, purpose and meaning, alive clear to your fingertips, tingling with vitality, (p. 28)

    Carlyon identifies the major barriers to wellness not as smoking or cholesterol, but as racism, sexism, and prejudice in all forms; bigotry and intolerance; social Darwinism; the combat approach to human relations—competitiveness, anti-intellectualism, nationalism, and militarism. He warns that many wellness enthusiasts display just these attitudes, which they should be fighting against.

    An epidemiology of wellness is emerging that can provide guidance to our efforts at health promotion but it will be concerned with far different health states than the mortality, morbidity, and disability measured by traditional disease-centered epidemiology. The epidemiology of wellness will be concerned with such health states and causal influences as love, creativity, humor, happiness, flexibility, self-esteem, and joy-of-living.

Recommended Readings

Carlyon, W. H. (1984). Disease prevention/health promotion—Bridging the gap to wellness. Health Values, 8(3), 27-30.

Duncan, D. F. (1985). The Peckham Experiment: A pioneering exploration of wellness. Health Values, 9(5), 40-43.

Duncan, D. F., & Gold, R. S. (Eds.). (1986). Special issue: Health promotion through the life cycle. Health Values, 10(3), entire issue.

Dunn, H. L. (1957). Points of attack for raising the levels of wellness. Journal of the National Medical Association, 49, 225-235.

Terris, M. (1975). Approaches to an epidemiology of health. American Journal of Public Health, 65,1037-1045.

Terris, M. (1980). Epidemiology as a guide to health policy. Annual Review of Public Health, 1, 323-344.

1The discussion in this and the following section is based largely on the contributions of the late Dr. Milton Terris, distinguished epidemiologist, past president of both the American Public Health Association and the National Association for Public Health Policy, and founding editor of the Journal of Public Health Policy.

2However, it is possible that some diseases normally thought of as noninfectious may actually have infectious agents. Cancer, for instance, may have a viral agent. The same is true of diabetes mellitus. If these hypotheses are true, then infectious diseases account for about one-third of all deaths.

(c) David F. Duncan, 2007
originally published by Macmillan Publishing Co., 1988


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