Chapter 10: Prevention



Most doctors are attracted to medicine because they look forward to curing disease. But all things considered, most people would prefer never to contract a disease in the first place—or, if they cannot avoid an illness, they prefer that it be caught early and stamped out before it causes them any harm. To accomplish this, people without specific complaints undergo interventions to identify and modify risk factors to avoid the onset of disease or to find disease early in its course so that early treatment prevents illness. When these interventions take place in clinical practice, the activity is referred to as preventive care.

Preventive care constitutes a large portion of clinical practice [1]. Physicians should understand its conceptual basis and content. They should be prepared to answer questions from patients such as, “How much exercise do I need, Doctor?” or “I heard that a study showed antioxidants were not helpful in preventing heart disease. What do you think?” or “There was a newspaper ad for a calcium scan. Do you think I should get one?”

Much of the scientific approach to prevention in clinical medicine has already been covered in this book, particularly the principles underlying risk, the use of diagnostic tests, disease prognosis, and effectiveness of interventions. This chapter expands on those principles and strategies as they specifically relate to prevention.

Preventive Activities in Clinical Settings

In the clinical setting, preventive care activities often can be incorporated into the ongoing care of patients, such as when a doctor checks the blood pressure of a patient complaining of a sore throat or orders pneumococcal vaccination in an older person after dealing with a skin rash. At other times, a special visit just for preventive care is scheduled; thus the terms annual physical, periodic checkup, or preventive health examination.

Types of Clinical Prevention

There are four major types of clinical preventive care: immunizations, screening, behavioral counseling (sometimes referred to as lifestyle changes), and chemoprevention. All four apply throughout the life span.


Childhood immunizations to prevent 15 different diseases largely determine visit schedules to the pediatrician in the early months of life. Human papillomavirus (HPV) vaccinations of adolescent girls has recently been added for prevention of cervical cancer. Adult immunizations include diphtheria, pertussis, and tetanus (DPT) boosters and well as vaccinations to prevent influenza, pneumococcal pneumonia, and hepatitis A and B.


Screening is the identification of asymptomatic disease or risk factors. Screening tests start in the prenatal period (such as testing for Down syndrome in the fetuses of older pregnant women) and continue throughout life (e.g., when inquiring about hearing in the elderly). The latter half of this chapter discusses scientific principles of screening.

Behavioral Counseling (Lifestyle Changes)

Clinicians can give effective behavioral counseling to motivate lifestyle changes. Clinicians counsel patients to stop smoking, eat a prudent diet, drink alcohol moderately, exercise, and engage in safe sexual practices. It is important to have evidence that (i) behavior change decreases the risk for the condition of interest, and (ii) counseling leads to behavior change before spending time and effort on this approach to prevention (see Levels of Prevention later in the chapter).


Chemoprevention is the use of drugs to prevent disease. It is used to prevent disease early in life (e.g., folate during pregnancy to prevent neural tube defects and ocular antibiotic prophylaxis in all newborns to prevent gonococcal ophthalmia neonatorum) but is also common in adults (e.g., low-dose aspirin prophylaxis for myocardial infarction, and statin treatment for hypercholesterolemia).

Levels of Prevention

Merriam-Webster’s dictionary defines prevention as “the act of preventing or hindering” and “the act or practice of keeping something from happening” [2]. With these definitions in mind, almost all activities in medicine could be defined as prevention. After all, clinicians’ efforts are aimed at preventing the untimely occurrences of the 5 Ds: death, disease, disability, discomfort, and dissatisfaction (discussed in Chapter 1). However, in clinical medicine, the definition of prevention has traditionally been restricted to interventions in people who are not known to have the particular condition of interest. Three levels of prevention have been defined: primary, secondary, and tertiary prevention (Fig. 10.1).

Figure 10.1. Levels of prevention.

Levels of prevention.

Primary prevention prevents disease from occurring. Secondary prevention detects and cures disease in the asymptomatic phase. Tertiary prevention reduces complications of disease.

Primary Prevention

Primary prevention keeps disease from occurring at all by removing its causes. The most common clinical primary care preventive activities involve immunizations to prevent communicable diseases, drugs, and behavioral counseling. Recently, prophylactic surgery has become more common, with bariatric surgery to prevent complications of obesity, and ovariectomy and mastectomy to prevent ovarian and breast cancer in women with certain genetic mutations.

Primary prevention has eliminated many infectious diseases from childhood. In American men, primary prevention has prevented many deaths from two major killers: lung cancer and cardiovascular disease. Lung cancer mortality in men decreased by 25% from 1991 to 2007, with an estimated 250,000 deaths prevented [3]. This decrease followed smoking cessation trends among adults, without organized screening and without much improvement in survival after treatment for lung cancer.

Heart disease mortality rates in men have decreased by half over the past several decades [4] not only because medical care has improved, but also because of primary prevention efforts such as smoking cessation and use of antihypertensive and statin medications. Primary prevention is now possible for cervical, hepatocellular, skin and breast cancer, bone fractures, and alcoholism.

A special attribute of primary prevention involving efforts to help patients adopt healthy lifestyles is that a single intervention may prevent multiple diseases. Smoking cessation decreases not only lung cancer but also many other pulmonary diseases, other cancers, and, most of all, cardiovascular disease. Maintaining an appropriate weight prevents diabetes and osteoarthritis, as well as cardiovascular disease and some cancers.

Primary prevention at the community level can also be effective. Examples include immunization requirements for students, no-smoking regulations in public buildings, chlorination and fluoridation of the water supply, and laws mandating seatbelt use in automobiles and helmet use on motorcycles and bicycles. Certain primary prevention activities occur in specific occupational settings (use of earplugs or dust masks), in schools (immunizations), or in specialized health care settings (use of tests to detect hepatitis B and C or HIV in blood banks).

For some problems, such as injuries from automobile accidents, community prevention works best. For others, such as prophylaxis in newborns to prevent gonococcal ophthalmia neonatorum, clinical settings work best. For still others, clinical efforts can complement community-wide activities. In smoking prevention efforts, clinicians help individual patients stop smoking and public education, regulations, and taxes prevent teenagers from starting to smoke.

Secondary Prevention

Secondary prevention detects early disease when it is asymptomatic and when treatment can stop it from progressing. Secondary prevention is a two-step process, involving a screening test and follow-up diagnosis and treatment for those with the condition of interest. Testing asymptomatic patients for HIV and routine Pap smears are examples. Most secondary prevention is done in clinical settings.

As indicated earlier, screening is the identification of an unrecognized disease or risk factor by history taking (e.g., asking if the patient smokes), physical examination (e.g., a blood pressure measurement), laboratory test (e.g., checking for proteinuria in a diabetic), or other procedure (e.g., a bone mineral density examination) that can be applied reasonably rapidly to asymptomatic people. Screening tests sort out apparently well persons (for the condition of interest) who have an increased likelihood of disease or a risk factor for a disease from people who have a low likelihood. Screening tests are part of all secondary and some primary and tertiary preventive activities.

A screening test is usually not intended to be diagnostic. If the clinician and/or patient are not committed to further investigation of abnormal results and treatment, if necessary, the screening test should not be performed at all.

Tertiary Prevention

Tertiary prevention describes clinical activities that prevent deterioration or reduce complications after a disease has declared itself. An example is the use of beta-blocking drugs to decrease the risk of death in patients who have recovered from myocardial infarction. Tertiary prevention is really just another term for treatment, but treatment focused on health effects occurring not so much in hours and days but months and years.

For example, in diabetic patients, good treatment requires not just control of blood glucose. Searches for and successful treatment of other cardiovascular risk factors (e.g., hypertension, hypercholesterolemia, obesity, and smoking) help prevent cardiovascular disease in diabetic patients as much, and even more, than good control of blood glucose. In addition, diabetic patients need regular ophthalmologic examinations for detecting early diabetic retinopathy, routine foot care, and monitoring for urinary protein to guide use of angiotensin-converting enzyme inhibitors to prevent renal failure. All these preventive activities are tertiary in the sense that they prevent and reduce complications of a disease that is already present.

Confusion about Primary, Secondary, and Tertiary Prevention

Over the years, as more and more of clinical practice has involved prevention, the distinctions among primary, secondary, and tertiary prevention have become blurred. Historically, primary prevention was thought of as primarily vaccinations for infectious disease and counseling for healthy lifestyle behaviors, but primary prevention now includes prescribing antihypertensive medication and statins to prevent cardiovascular diseases, and performing prophylactic surgery to prevent ovarian cancer in women with certain genetic abnormalities.

Increasingly, risk factors are treated as if they are diseases, even at a time when they have not caused any of the 5 Ds. This is true for a growing number of health risks, for example, low bone mineral density, hypertension, hyperlipidemia, obesity, and certain genetic abnormalities. Treating risk factors as disease broadens the definition of secondary prevention into the domain of traditional primary prevention.

In some disciplines, such as cardiology, the term secondary prevention is used when discussing tertiary prevention. “A new era of secondary prevention” was declared when treating patients with acute coronary syndrome (myocardial infarction or unstable angina) with a combination of antiplatelet and anticoagulant therapies to prevent cardiovascular death [5]. Similarly, “secondary prevention” of stroke is used to describe interventions to prevent stroke in patients with transient ischemia attacks.

Tests used for primary, secondary, and tertiary prevention, as well as for diagnosis, are often identical, another reason for confusing the levels of prevention (and confusing prevention with diagnosis). Colonoscopy may be used to find a cancer in a patient with blood in his stool (diagnosis); to find an early asymptomatic colon cancer (secondary prevention); remove an adenomatous polyp, which is a risk factor for colon cancer (primary prevention); or to check for cancer recurrence in a patient treated for colon cancer (a tertiary preventive activity referred to as surveillance).

Regardless of the terms used, an underlying reason to differentiate levels among preventive activities is that there is a spectrum of probabilities of disease and adverse health effects from the condition(s) being sought and treated during preventive activities, as well as different probabilities of adverse health effects from interventions that are used for prevention at the various levels. The underlying risk of certain health problems is usually much higher in diseased than healthy people. For example, the risk of cardiovascular disease in diabetics is much greater than in asymptomatic non-diabetics.

Identical tests perform differently depending on the level of prevention. Furthermore, the trade-offs between effectiveness and harms can be quite different for patients in different parts of the spectrum. False-positive test results and overdiagnosis (both discussed later in this chapter) among people without the disease being sought are important issues in secondary prevention, but they are less important in treatment of patients already known to have the disease in question. The terms primary, secondary, and tertiary prevention are ways to consider these differences conceptually.

Scientific Approach to Clinical Prevention

When considering what preventive activities to perform, the clinician must first decide with the patient which medical problems or diseases they should try to prevent. This statement is so clear and obvious that it would seem unnecessary to mention, but the fact is that many preventive procedures, especially screening tests, are performed without a clear understanding of what is being sought or prevented.

For instance, physicians performing routine checkups on their patients may order a urinalysis. However, a urinalysis might be used to search for any number of medical problems, including diabetes, asymptomatic urinary tract infections, renal cancer, or renal failure. It is necessary to decide which, if any, of these conditions is worth screening for before undertaking the test.

One of the most important scientific advances in clinical prevention has been the development of methods for deciding whether a proposed preventive activity should be undertaken [6]. The remainder of this chapter describes these methods and concepts.

Three criteria are important when judging whether a condition should be included in preventive care (Table 10.1):

Table 10.1. Criteria for Deciding Whether a Medical Condition Should Be Included in Preventive Care

1. How great is the burden of suffering caused by the condition in terms of:
Death Discomfort
Disease Dissatisfaction
Disability Destitution
2. How good is the screening test, if one is to be performed, in terms of:
Sensitivity Safety
Specificity Acceptability
3. A. For primary and tertiary prevention, how good is the therapeutic intervention in terms of:
  • Effectiveness
  • Safety
  • Cost-effectiveness
B. For secondary prevention, if the condition is found, how good is the ensuing treatment in terms of:
  • Effectivenes
  • Safety
  • Early treatment after screening being more effective than later treatment without screening, when the patient becomes symptomatic
  • Cost-effectiveness
  1. The burden of suffering caused by the condition.
  2. The effectiveness, safety, and cost of the preventive intervention or treatment.
  3. The performance of the screening test.

Burden of Suffering

Only conditions posing threats to life or health (the 5 Ds in Chapter 1) should be included in preventive care. The burden of suffering of a medical condition is determined primarily by (i) how much suffering (in terms of the 5 Ds) it causes those afflicted with the condition, and (ii) its frequency.

How does one measure suffering? Most often, it is measured by mortality rates and frequency of hospitalizations and amount of health care utilization caused by the condition. Information about how much disability, pain, nausea, or dissatisfaction a given disease causes is much less available.

The frequency of a condition is also important in deciding about prevention. A disease may cause great suffering for individuals who are unfortunate enough to get it, but it may occur too rarely—especially in the individual’s particular age group—for screening to be considered. Breast cancer is an example. Although it can occur in much younger women, most breast cancers occur in women older than 50 years of age.

For 20-year-old women, annual breast cancer incidence is 1.6 in 100,000 (about one-fifth the rate for men in their later 70s) [7]. Although breast cancer should be sought in preventive care for older women, it is too uncommon in average 20-year-old women and 70-year-old men for screening. Screening for very rare diseases means not only that, at most, very few people will benefit, but screening also results in false-positive tests in some people who are subject to complications from further diagnostic evaluation.

The incidence of what is to be prevented is especially important in primary and secondary prevention because, regardless of the disease, the risk is low for most individuals. Stratifying populations according to risk and targeting the higher-risk groups can help overcome this problem, a practice frequently done by concentrating specific preventive activities on certain age groups.