The renowned medical historian Henry Sigerist, writing in 1941, listed the main items that must be included in a national health program. The first three items were free education, including health education, for all; the best possible working and living conditions; and the best possible means of rest and recreation. Medical care rated only fourth on his list (Terris, 1992a). For Sigerist (1941), medical care was

Many people working in the fields of medical care and public health believe that “prevention has broken down” too often because society has dedicated insufficient resources and commitment to prevention.

Primary prevention seeks to avert the occurrence of a disease or injury (e.g., immunization against polio; taxes on the sale of cigarettes to reduce their affordability, and thereby their use). Secondary prevention refers to early detection of a disease process and intervention to reverse or retard the condition from progressing (e.g., Pap smears to screen for premalignant and malignant lesions of the cervix, and mammograms for early detection of breast cancer).

The promotion of good health and the prevention of illness encompass three distinct levels or strategies (Terris, 1986; Table 11-1):

1. 
   

   The first and broadest level includes measures to address the fundamental social determinants of illness; as evidence presented in Chapter 3 shows, lower income is associated with higher morbidity and mortality rates. Improvement in the standard of living and social equity (e.g., through job creation programs to reduce or eliminate unemployment) may have a greater impact on preventing disease than specific public health programs or medical care services.

   
   
2. 
   

   The second level of prevention involves public health interventions to reduce the incidence of illness in the population as a whole. Examples are water purification systems, the banning of cigarette smoking in the workplace, and public health education on human immunodeficiency virus (HIV) prevention in the schools. These strategies generally consist of primary prevention. The 2.6% figure cited in the opening paragraph represents these public health activities.

   
   
3. 
   

   The third level of prevention involves individual health care providers performing preventive interventions for individual patients; these activities can be either primary or secondary prevention. The US Preventive Services Task Force and other organizations have established regular schedules for preventive medical care services (US Preventive Services Task Force, 2014).

Until modern times, the conditions that produced the greatest amount of illness and death in the population were infectious diseases. The initial decline of infectious disease mortality rates took place even before the cause of these illnesses was understood. In the 18th and 19th centuries, food production increased markedly throughout the Western world. By the early 19th century, infectious disease mortality rates were dropping in England, Wales, and Scandinavia, probably as a result of improved nutrition that allowed individuals, particularly children, to resist infectious agents. Thus, the initial success of illness prevention took place through the improvement of overall living conditions rather than from specific public health or medical interventions (McKeown, 1990).

In the 19th century, scientists and public health practitioners discovered many of the agents causing infectious diseases. By comprehending the causes (such as bacteria and viruses) and the risk factors (e.g., poverty, overcrowding, poor nutrition, and contaminated water) associated with these illnesses, public health measures (such as water purification, sewage disposal, and pasteurization of milk) were implemented that drastically reduced their incidence. This was the first epidemiologic revolution (Terris, 1985).

From 1870 to 1930, the death rate from infectious diseases fell rapidly. Medical interventions, whether immunizations or treatment with antibiotics, were introduced only after much of the decline in infectious disease mortality had taken place. The first effective treatment against tuberculosis, the antibiotic streptomycin, was developed in 1947, but its contribution to the decrease in the tuberculosis death rate since the early 19th century has been estimated to be a mere 3%. For whooping cough, measles, scarlet fever, bronchitis, and pneumonia, mortality rates had fallen to similarly low levels before immunization or antibiotic therapy became available. Pasteurization and water purification were probably the main reason for the decline in infant mortality rates (McKeown, 1990).

Some illnesses are exceptions to the rule that infectious disease mortality is influenced more by improved living standards and public health measures than by medical interventions. Immunization for smallpox, polio, and tetanus and antimicrobial therapy for syphilis had a substantial impact on mortality rates from those illnesses. Considering infectious diseases as a group, however, medical measures probably account for less than 5% of the decrease in mortality rates for these conditions over the past century (McKinlay et al., 1989; McKeown, 1990).

As infectious diseases waned in importance during the first half of the 20th century and as life expectancy increased, rates of noninfectious chronic illness grew rapidly. Eleven infectious diseases accounted for 40% of total deaths in the United States in 1900, but less than 10% in 1980. In contrast, heart disease, cancer, and stroke (cerebrovascular disease) caused 16% of total deaths in 1900 but 64% by 1980 (McKinlay et al., 1989).

Fifty years ago, epidemiologists did not understand the causes of noninfectious chronic diseases.

During the second epidemiologic revolution, it was learned that the major illnesses in the United States have a few central causes and are in large part preventable. In 2013, 2.6 million people died in the United States (Table 11-2). A surprisingly small number of risk factors are implicated in 40% of these deaths. It has been estimated that use of tobacco causes 480,000 fatalities, an unhealthful diet and inactivity contributes to 460,000 more, and alcohol is responsible for 88,000 deaths annually in the United States (Centers for Disease Control and Prevention, 2014). By discovering and educating the population about the risk factors of smoking, unhealthful diet, and lack of exercise, the second epidemiologic revolution has already shown success. From 1980 to 2006, age-adjusted mortality rates for coronary heart disease (CHD) declined by an astonishing 67% (Fig. 11-2). This decline was associated with reduced rates of tobacco use and lowered mean serum cholesterol levels in the population. As with infectious diseases a century earlier, this decline was mostly related to public health interventions regarding smoking and diet. The unfortunate side of this success story is that those in the poorest socioeconomic position and the least education have considerably higher mortality rates than those with higher socioeconomic status (Zheng, 2012).

Chronic disease prevention may be viewed from two distinct perspectives: that of the individual and that of the population (Rose, 1985). The medical model seeks to identify high-risk individuals and offer them individual protection, often by counseling on such topics as smoking cessation and low-fat diet. The public health approach seeks to reduce disease in the population as a whole, using such methods as mass education campaigns to counter drinking and driving, the taxation of tobacco to drive up its price, and the labeling of foods to indicate fat and cholesterol content. Both approaches have merits but the medical model suffers from some drawbacks.

The individual-centered approach of the medical model may produce tunnel vision regarding the causation, and thus the prevention, of disease. Let us take the example of cholesterol.

Ancel Keys (1970) performed a famous study comparing CHD in different nations. In east Finland, CHD was common, 20% of diet calories came from saturated fat, and 56% of men aged 40 to 59 years had cholesterol levels greater than 250 mg/dL. In Japan, CHD was rare, 3% of calories were provided by saturated fat, and only 7% of men aged 40 to 59 years had cholesterol levels above 250 mg/dL. If we compared two individuals in east Finland who eat the same diet, one with a cholesterol level of 200 mg/dL and the other with a level of 300 mg/dL, we might conclude that variation in cholesterol levels among individuals is caused by genetic or other factors, but not diet. If, on the other hand, we look at entire populations, studying the average cholesterol level and the percentage of fat in the diet in east Finland and in Japan, we will conclude that high-fat diets correlate with high levels of cholesterol and with high rates of CHD.

Individual variations within each country are often of less importance than variations between one nation and another. The clues to the causes of diseases “must be sought from differences between populations or from changes within populations over time” (Rose, 1985).