Public Health Exam 3 Textbook info

9 actual causes of death

1. Tobacco, poor diet and physical inactivity, alcohol consumption, microbial agents, toxic agents, motor vehicles, firearms, sexual behavior, illicit drug use. These nine actual causes of death account for approximately 50 percent of all deaths in the United States. The other half includes genetic factors, which were specifically excluded from the analysis, and other less clearly identifiable causes. Lack of access to health care was cited as a significant factor. This problem should be alleviated by the new health care law passed during the Obama administration. Presumably, many deaths could legitimately be attributed to old age. The nine identified factors are of particular public health significance because they cause premature deaths; they are often preceded by impaired quality of life; and many could be prevented by public health measures.

Stress and social support

A number of psychological factors have been found to influence health, some of which may have a role in the health effects of SES. One of these factors is stress, which is due to the adverse physical and social conditions associated with lower SES, which may act both directly, by affecting physiological processes, and indirectly, by influencing indi- vidual behavior. Early evidence of the health effects of stress came from observations that widows and widowers seemed to have an unusually high risk of dying soon after the death of their spouses. Several studies in the 1960s and 1970s found that mortality rates of survivors are 40 percent to 50 percent higher during the six months after the death of a spouse compared to the mortality of married people of the same age. These studies were expanded to include the effects of other stressful life events such as death of other family members, divorce, and loss of a job, all of which were found to increase the risk of illness or death.8 Stress is well established as a contributor to heart disease, a relationship that has been demonstrated in a variety of epidemiologic studies. A particularly convincing example is a study of the male employees of two banks. At first, the two groups were similar, but one bank changed its management policies to become commercial. The employees of the commercial bank had to deal with considerable competition, risk, and responsibility for investing funds; employees of the other bank, a semipublic sav- ings bank, had less competition and fewer responsibilities. Over a 10-year period, the employees of the commercial bank were found to have 50 percent higher rates of heart attacks and sudden death.9 Experiments on animals ranging from rats to baboons have found that various psychosocial stresses induce physiological changes such as decreased immune response and increased atherosclerosis. A 1991 experiment on humans demonstrated that stress suppresses the immune response in humans also. In that experiment, investigators measured levels of psychological stress in 420 healthy volunteers, then administered nasal drops containing cold viruses to all but a small control group. They found that the subjects whose stress levels were higher were more likely to be infected with cold viruses and more likely to develop colds, with symptoms including sneezing, coughing, eye watering, nasal discharge, sore throat, and increased use of tissues.10 A whole new field of research called psychoneuroimmunology has arisen to study the impact of stress on health. There are many reasons why lower SES exposes people to greater life stress. Daily hassles are greater at lower levels on the SES hierarchy: Cars break down, landlords complain about late rent checks, child care is unreliable, officials are rude. Members of racial and ethnic minorities may be exposed to incidents of racial prejudice. These minor but constant stresses may be as debilitating as such major life events as deaths in the family. Higher income and education provide resources that help to buffer the impact of life's hassles, thereby protecting health. A number of factors can help people cope with life's stresses. Money, of course, can solve a multitude of problems. Education is important because it provides the information and skills to solve problems. Family and friends can also help by providing both emotional and instrumental assistance. In fact, social support has proven to be surprisingly significant in determining an individual's health.

transtheoretical model,

A theory that has proved widely useful in health education is the transtheoretical model, which envisions change—for example, smoking cessation or adopting a healthy diet—as a process involving progress through a series of five stages: precontemplation, contemplation, preparation, action, and maintenance. People in the precontemplation stage have no intention to change their behavior; the first step in getting them to change involves consciousness- raising to increase their awareness that their behavior is unhealthy and should be changed. In the second, contemplation stage, the person is more aware of the benefits of change, but is also very aware of the difficulties and barriers to change and still is not ready to take action. The third step is preparation, when a person has decided to make the change and has planned concrete actions he or she could take, such as signing up for a class, discussing the plan with their physician, or buying a self-help book. The fourth step, action, requires that individuals actually modify their behavior by abstaining from smoking or adhering to a healthier diet. Finally, maintenance is the stage in which people have achieved the healthier behavior but must strive to prevent relapse.16 Knowing which stage an individual has reached can help a physician or health educator move him or her along to the next stage.

Attempt to eradicate an eradicable disease

An attempt to eradicate an eradicable disease can backfire if it is not conducted with sufficient political will, knowledge, and resources. This was the case with malaria, which was the target of an international eradication campaign in the 1950s and 1960s. There is no nonhuman reservoir for the malaria-causing parasites, but the route of transmission is a vector, a certain species of mosquito. The primary weapon in the eradication effort wasthepesticideDDT.Whilethecampaignproduceddramaticresults,fundingranout before the objective was achieved, and there was a resurgence of the disease with greater impact than ever. A combination of factors contributed to the calamity: DDT-resistant mosquitoes emerged; the pathogen developed resistance to the main antimalarial drug, chloroquine; and populations in former malarial areas lost their immunity to the disease because of lack of exposure.25 Now, malaria is one of the most widespread potentially fatal infectious diseases in the world, killing an estimated one million people annually, mainly children.26 The disease occurs mainly in tropical and subtropical areas and has been largely eliminated in the United States, but global climate change and international travel could contribute to the re-emergence of malaria as a public health problem in the South.

ecological model

An ecological model looks at how the social environment, including interpersonal, organizational, community, and public policy factors, supports and maintains unhealthy behaviors. The model proposes that changes in these factors will produce changes in individual behavior. The ecological model, illustrated in (Figure 14-2), describes five levels of influence that determine health-related behaviors; each level is a potential target for health promotion intervention. The first level—intrapersonal factors—encompasses the knowledge, attitudes, and skills of the individual. This is the level that has been explored by the psychological theories discussed earlier in this chapter. The second through fifth levels—interpersonal relations, institutional factors, community factors, and public policy—each have an impact on individual behavior both directly and indirectly, by interaction with the factors at other levels of influence. The second level of influence, interpersonal relations—including family, friends, and coworkers—has very important effects on health-related behavior. Families, of course, are the origin of many health behaviors, especially habits learned early in life such as tooth brushing, exercising, and eating patterns. In the teen years, pressure from peers becomes more significant in influencing individual behaviors, such as smoking, using alcohol and drugs, and engaging in other risk-taking behavior. On the positive side, family and peer relationships provide the social support discussed earlier in this chapter.

self efficacy

Another important concept in understanding health behavior is self-efficacy, the sense of having control over one's life. People who are confident that they can control their lives are said to have high self-efficacy. People who believe their lives are subject to chance or external forces are said to have low self-efficacy. Self-efficacy is often added as a fifth factor in the health belief model. People are more likely to adopt healthy behavior if they are confident that they have the ability to do so.13 A sense of control is beneficial for health in a number of ways. Clearly, it reduces stress. A number of studies in both humans and animals have shown that an individual's perception of the stressfulness of an adverse event can be reduced by two factors: knowledge of when the stressful event will occur and the ability to regulate the timing and intensity of the event. This knowledge and ability give the individual a sense of control, or self-efficacy. The lowest self-efficacy is seen in people (or animals) who have experience of being unable to avoid noxious events, especially if they have repeatedly tried and failed. They may develop a pattern of "learned helplessness," a pattern described as a "numbed acceptance of a negative situation, so that an individual no longer tries to change that situation for the better because he or she does not expect those efforts to make any difference."14(p.44) A number of studies have shown that people with high self-efficacy are more likely to engage in health-promoting behavior than those with low self-efficacy. An attitude of learned helplessness is common in people who have repeatedly tried and failed to quit smoking or lose weight. A great deal of research has been focused on how to increase people's self-efficacy, thereby helping to motivate them to practice healthy behaviors. An individual's self- efficacy is increased by previous successful performance of the behavior in question. It may also be increased by seeing others successfully perform the behavior, especially if the observed behavior is being performed by someone similar to themselves. For example, the most successful school drug prevention programs include role-modeling, small group exercises, and skills practice to teach students how to identify and resist internal and external pressures to use drugs. These programs have been found to be much more effective in enhancing students' self-efficacy to resist drugs if they are led by older teens, with whom they can identify, rather than by adult health educators.15

social norms approach

Another variation on health education that has become popular with college adminis- trators to curb high-risk student drinking is the social norms approach. This approach is based on an influential study from the 1980s, which surveyed students about their perception of the frequency and amount of drinking among their peers. It turned out that students generally believed that other students drank more than they actually did. The remedy to the misperception that "everyone is doing it" is to advertise the actual norms on campus. Institutions could reduce high-risk drinking by up to 20 percent over a relatively short period of time by conducting surveys on campus and advertising the results.13 Although use of the social norms approach is in an early stage, its proponents believe it can be used for a variety of other issues, such as tobacco prevention, seat-belt use, and prevention of high-risk sexual activity.

Health promotion programs

As social and behavioral scientists gain a better understanding of how people's behavior is affected by their own beliefs and by the various levels of influence in their social environment, theories such as the health belief model and the ecological model are being used to design more effective public health and disease prevention programs. A good example is provided by an AIDS prevention program targeted at gay men in San Francisco in the mid-1980s.18 Prevention of infection through behavior change was and is still the most effective approach to AIDS control because there is as yet no biomedical solution to the problem—no vaccine and no proven cure.

The fifth level: public policy

At the fifth level, public policy encompasses the regulations and limitations on behavior that have been discussed previously. These are the most explicit and controversial measures that local, state, and national governments take to promote healthy behaviors. Such measures include smoking restrictions, age limits on alcohol sales, seat-belt laws, and so forth.

Because health is so strongly affected by behavior

Because health is so strongly affected by behavior, it is important for public health advocates to understand what influences people to behave in healthy or unhealthy ways. The social and behavioral sciences offer insights into why people behave as they do, and they provide a basis for developing interventions aimed at persuading people to change their behavior.

Public health has had great success in controlling infectious diseases.

Classic public health measures prevent transmission of disease-causing bacteria, viruses, and parasites by inter- rupting the chain of infection. Measures employed at various links in the chain include killing the pathogen, eliminating the reservoir that harbors the pathogen, preventing transmission from one host to another or from reservoir to host, and increasing the resistance of hosts by immunization.

Contact tracing

Contact tracing is also routinely used for controlling sexually transmitted diseases, such as syphilis and gonorrhea. Syphilis, which tends to affect the poor, the homeless, drug users, and prostitutes, can be diagnosed by a blood test. Because it has few symptoms in the early stages, it may go untreated and is easily spread. The challenge for public health is to identify those with the disease through screening programs carried out, for example, in a city jail. Once a case is identified, public health workers try to discreetly alert those who have been exposed. The public health worker asks the person who has been diagnosed to identify sexual contacts; the worker then notifies the contacts that they have been exposed without identifying the source of the exposure. Syphilis is readily cured by penicillin. If untreated, it may cause long-term damage to the heart and brain; congenital syphilis in infants born to infected mothers can be lethal.

chain of infection

Control of infectious diseases is still an important component of public health. The public health approach to controlling infectious diseases is to interrupt the chain of infection. The chain of infection, a term used to describe the pattern by which an infectious disease is transmitted from person to person, is composed of several links

Education approach

Education about health includes simply informing people about risks, which can be an effective strategy when new knowledge becomes available, as occurred with the 1964 Surgeon General's report called Smoking and Health. Food labeling is also part of an educational effort to encourage Americans to eat a healthier diet.

How were epidemics controlled?

Epidemics of smallpox and cholera swept through the city every few years, killing many people in each wave. In the mid-19th century, background mortality rates—largely from tuberculosis, typhoid, and miscellaneous respiratory and gastrointestinal diseases—were double what they became by 1930. These infectious diseases were largely conquered through public health mea- sures, including purification of water, proper disposal of sewage, pasteurization of milk, and immunization, as well as improved nutrition and personal hygiene. The discovery and introduction of antibiotics in the 1940s also played a role. In fact, by the 1960s, the threat of infectious diseases seemed to have been reduced to a minor nuisance.

Epidemiologic surveillance

Epidemiologic surveillance is the system by which public health practitioners watch for disease threats so that they may step in and break the chain of infection, halting the spread of disease. In the early history of public health, the solution was often quarantine— isolation of the patient to prevent him or her from infecting others. Quarantine is still used occasionally, when the disease is serious and there is no effective vaccine. For example, a patient diagnosed with tuberculosis—which is slow to respond to medication—might be ordered to stay home for 2 to 4 weeks after treatment is started until the disease is no longer infectious. More often, the public health response when an outbreak is detected by surveillance is to locate people who have had contact with the infected individual and to immunize them or give them medical treatment, as appropriate. For tuberculosis, contact tracing is used in addition to quarantine: people who have been exposed to the patient are given prophy- lactic doses of antibiotics. Tuberculosis has presented new and more difficult problems to the public health system in recent years because of the development of drug-resistant strains of the bacteria.

Small pox

For some infectious diseases, however, no bacterial agent could be found. Smallpox, for example, was known to be transmitted from a sick person to a healthy one by something in the pus of the patient's lesions. Yet attempts to isolate a microorganism were unsuc- cessful. The agent that caused the disease could pass through the finest available filters and could not be observed in any existing microscope. Smallpox was recognized to be one of a number of diseases caused by such "filterable agents" or viruses. It was not until 1935, when the American scientist W. M. Stanley crystallized tobacco mosaic virus, that the nature of viruses was demonstrated.

Means of transmission: Gastrointestinal infections

Gastrointestinal infections such as cholera, cryptospiridiosis, and diphtheria are generally spread by the fecal-oral route, by which fecal matter from an infected person reaches the mouth of an uninfected person. This may occur as a result of poor personal hygiene or by contamination of drinking water because of inadequate sanitary systems. Vector-borne diseases, including malaria, yellow fever, and West Nile encephalitis, gener- ally use a more complex route from one person to another, most often through an insect.

regulation

Governments have always regulated people's behavior by passing and enforcing laws. The regulatory approach is clearly warranted when its intent is to restrain people from harming others. Laws against murder and assault are in effect public health laws, and there is no question about their legitimacy. Traffic laws—also aimed at protecting public health—are clearly accepted as necessary. Though not scrupulously obedient, everyone recognizes the importance of stopping at red lights, keeping to the right side of the road (in the United States), and driving at speeds appropriate to the conditions.

Doctor visit

Health education messages may also be delivered by a medical professional during an office visit. Doctors who care for people with chronic diseases such as diabetes and asthma know that they can keep their patients healthier if they include a health education component in their treatment plans. Studies have shown that, while patients do not always follow the doctor's orders, a physician's recommendation can increase the likelihood that people will change their behavior.14

individual belief and behaviors

In accordance with the recognition that individual beliefs and behaviors occur in a social context and that health promotion may be more effectively achieved through changing the social environment, so-called ecological models have been proposed for understanding health behavior.17

Health promotion program example

In the 1980s, San Francisco was the city with the second highest number of AIDS cases in the United States. Most of the cases occurred in gay men, and the primary means by which the virus was transmitted was by sexual intercourse between men. Almost as soon as this was understood, a prevention campaign was launched by the city health department in collaboration with community-based AIDS organizations and a research group from the University of California. They mounted an intensive media effort to inform at-risk individuals about the practice of safer sex. However, researchers understood that merely providing knowledge was not sufficient to change people's behavior. By interviewing small groups of gay men, they identified key beliefs that must be addressed if the messages were to be acted on by the target population. This approach combines elements of three theories discussed above: the health belief model, self-efficacy, and the ecological model. The campaign's goals were to promote the following beliefs among high-risk individuals: 1. Belief in personal threat (i.e.,"I am susceptible to infection"). 2. Belief in response efficacy (i.e.,"There is something I can do that will lessen the threat of infection"). 3. Belief in personal efficacy (i.e.,"I am capable of making these changes"). 4. Beliefthatnewbehaviorsareconsistentwithgroupnorms(i.e.,"Mypeerssupport new behaviors"). The first belief was relatively easy to achieve because of the extensive publicity about AIDS in the general media. News and entertainment media aimed at gay men, including gay newspapers, comic books and leaflets, and telephone hot lines could be used to focus more on the second and third beliefs. Gay organizations held small group training sessions to teach skills in the use of condoms as well as interpersonal communication skills such as the ability to negotiate safer sex practices with prospective sex partners; this helped to enhance perceptions of self-efficacy among those at risk. To achieve the fourth belief, messages sought to encourage the perception that low-risk behaviors could be pleasurable and satisfying.

Means of transmission: infectious diseases

Infectious diseases are spread by a variety of routes, directly from one person to another or indirectly by way of water, food, or vectors such as insects and animals. Bacteria and viruses that cause respiratory infections, including colds, influenza, and tuberculosis, are transmitted through the air on aerosols, water droplets produced when an infected person coughs or sneezes. They can also be transmitted from an infected person to objects he or she touches, such as doorknobs, utensils, or towels, to be picked up by the next person to touch the contaminated object and transferred by hand to the nose. The early European settlers made use of this route of transmission to inflict a primitive form of germ warfare on the Native American people, giving them blankets that had been used by patients suf- fering from smallpox. The disease decimated Native American populations because they had no immunity to the virus.

The association is seen at all levels of the socioeconomic scale,

It is not only the effects of poverty that account for socioeconomic variations in health, however. The association is seen at all levels of the socioeconomic scale, the very rich being healthier than the rich, who are healthier than the middle class, and so on. In a study of British civil servants called the Whitehall Study, mortality rates over a 10-year period were compared across four employment grades. Top administrators were compared with executives and professionals, the clerical staff, and unskilled laborers.3 As seen in (Figure 14-1), higher employment status was associated with a lower risk of dying.

What is chapter 9 primarily about?

It will discuss the causes of infectious diseases, how they are transmitted, and how classic public health measures have brought them under control.

Measles

Measles, another viral disease that could in theory be eradicated, offers an example of what happens when public health relaxes its vigilance. Before a vaccine was available, almost all children contracted measles, causing 400 to 500 deaths a year in the United States and 4000 cases of chronic disability from measles encephalitis.20 A vaccine became available in 1963, and the number of cases in the United States dropped precipitously. In 1978, the U.S. Department of Health and Human Services set a goal to eradicate measles from this country by 1982. That ambition proved overly optimistic. One problem was that outbreaks of measles began to occur among high school and college students who had been vaccinated as babies. It became clear that the immunity conferred by vaccination in infancy wears off and that a booster vaccination is necessary in older children, a practice that is now recommended at the age of 4 to 6. The booster should be given to adolescents if they did not receive it earlier. Implementation of the new recommendations was widespread in the 1990s, and measles cases in the United States declined to low levels. In fact, measles was declared eliminated from the United States in 2000, meaning that all cases could be traced to individuals who contracted the disease outside the country and brought it here.20 However, in 2011, 222 measles cases were reported to the CDC, compared to a median of 60 per year during 2001 to 2010.21 Of the 2011 cases, 196 were American residents, the majority of them children, and 86 percent of them were unvaccinated or had unknown vaccination status. Of the 66 children who were unvaccinated but should have been, 50 were unvaccinated because of philosophical or religious beliefs, discussed later in this chapter. The year 2014 proved to be a bad year for measles. Six hundred forty-four cases were reported from 27 states, more than half of them among unvaccinated Amish children in Ohio.22 Then in December, a large outbreak began in California that spread across the country.23 The first reported case was an 11-year-old girl who had visited a Disney theme park in southern California during the exposure period and was hospitalized. She had not been vaccinated. The source of the exposure has not been identified, but the strain of the virus was the same as one that had recently caused a large outbreak in the Philippines and has also been detected in other countries. Disney theme parks attract many international visitors, one of which presumably carried the virus to California in 2014. Public health leaders had hoped that when and if polio is eradicated, the organizational and medical resources that had been mobilized in that campaign could then be used in a vaccination campaign against measles. Given the uncertainties with polio eradication and the difficulties with achieving universal immunization in the United States, the prospect for measles eradication worldwide is doubtful. Measles is still endemic in some European countries as well as at higher levels in Africa and Southeast Asia. However, progress has been made. The number of estimated deaths from measles has been reduced from 562,000 in 2000 to 122,000 in 2012.24

An extension of the educational approach to changing behavior is the use of advertising to reinforce the public health message.

Most people are subjected to large doses of media messages promoting unhealthy behavior, including cigarette ads in magazines, beer commercials on television, and movie portrayals of unsafe sex. The occasional public service announcements meant to convey countervailing messages are feeble weapons in the battle for public health, although there is evidence that counter advertising about the dangers of smoking helped to reduce smoking rates in the 1960s. The "Just Say No" antidrug campaign during the Reagan administration was strong enough to make an impression; whether it persuaded people to change their behavior is doubtful. Recently there have been efforts to develop more effective approaches to conveying public health messages in the media. One of these was the successful Harvard School of Public Health campaign to persuade several television producers to write "designated drivers" into their sitcom scripts as a way of advocating an alternative to drinking and driving.12

Education

Most simply, education informs the public about healthy and unhealthy behavior. Many people who are concerned about their health and that of their families do in fact adjust their behavior in accordance with new information. the focus of government educational programs on nutrition has shifted to the prevention of the major killers—cancer, cardiovascular disease, and diabetes, which tend to be associated with nutritional excesses. Research over the past several decades has led to a greater understanding of the importance of overall dietary pattern in the onset of these diseases. The government's educational efforts have stressed the importance of eating less fat (especially saturated fat), less salt, and more fruits, vegetables, and grains. The FDA has revised its labeling requirements to provide consumers with the information that will allow them to follow its guidelines. There is evidence that Americans have responded to the message that they should cut down on fat in their diet and that this behavior may have helped bring down the high rates of heart disease over the past 40 years.

Focus of Public health

Nevertheless, public health must find ways to improve the health of groups that have historically been disadvantaged economically, educationally, and politically. The federal government predicts that by 2050, nearly half of Americans will belong to racial and ethnic minorities. If the health disparities are not remedied, the overall health of the U.S. population is likely to decline.7 Public health interventions aimed at improving the health of minority groups include efforts to influence their health behaviors. These efforts begin with attempts to understand what factors influence health and health behavior, how these factors may affect people of various ethnic and racial groups differently, and what kind of interven- tions can be effective in modifying these factors. This chapter and later chapters that consider specific health behaviors will examine how minority groups differ from the majority white population and how those differences may be related to the observed disparities in health.

Why are people with higher SES are healthier

Part of the reason that people with higher SES are healthier seems to be that people with more education behave in healthier ways. For example, in 2013, 25.8 percent of Americans without a high school diploma smoked, while of those with a bachelor's degree or higher, only 7.7 percent smoked. Those with more education were also more physically active.4(Tables 52,63) Similarly, the Whitehall Study questioned subjects about their habits and found that those in higher employment grades were less likely to smoke, more likely to exercise, and more likely to eat a healthful diet that included skim milk, whole grains, and fresh fruits and vegetables.3

chain of infection pathogen component

Pathogen. The pathogen is a virus, bacterium, or parasite that causes the disease in humans.

Polio Virus

Poliovirus, like smallpox virus, infects human beings only, and polio similarly has the potential to be eradicated. In 1988, at a time when 350,000 children were being paralyzed each year, WHO set a goal of eradicating polio by the year 2000.16 This goal was not met, but substantial progress has been made against this crippling disease: polio has been essentially eliminated from the Western Hemisphere, Europe, Southeast Asia, and the Western Pacific, and by 1999, annual polio cases were reduced by 99 percent worldwide.17 Only three countries continue to have endemic polio—Nigeria, Pakistan, and Afghani- stan—but eradication from these countries has proven extremely difficult. Rumors spread in 2003 among Muslims, especially in Nigeria, that the polio vaccine had been deliberately contaminated to cause AIDS or infertility. Several Nigerian states halted vaccinations, the number of cases in Nigeria jumped to 800 in 2004, and the virus spread to several other African countries that had previously been polio free. Under pressure from WHO, Nigeria resumed polio immunizations the following year.16 However, as long as the disease exists anywhere, it tends to spread to neighboring countries; several countries, including Cam- eroon, Equatorial Guinea, Syria, and Iraq, have reestablished transmission.18 There are several reasons why polio is proving more difficult to eradicate than small- pox.19 Unlike smallpox, there are many "invisible" cases of polio, in which children may be infected, able to spread the virus by the fecal-oral route but not show symptoms. Thus it is not possible to focus on small outbreaks as was done with smallpox. The vaccine is imper- fect and must be administered several times to become effective. India has made major effort to vaccinate children with repeated rounds of National Immunization Days each year, but in poverty-stricken areas of the country children suffering from other intestinal infections tend not to develop immunity even after multiple doses of the vaccine. Politi- cal upheaval has interfered with immunization campaigns in some countries. In Pakistan and Nigeria, for example, polio vaccinators have been killed by Islamic extremists. Some experts have argued that the goal of eradicating polio is unrealistic and that efforts should be focused on "control" rather than eradication.19 They say that other vaccine-preventable diseases are being neglected because of the intensive effort on polio, that the campaign has been going on too long and has become too expensive. However, India was removed from the list of endemic countries in 2012, giving hope that success can be achieved elsewhere, and the effort continues.

Public health measures to control the spread of disease are aimed at

Public health measures to control the spread of disease are aimed at interrupting the chain of infection at whichever links are most vulnerable. At link 1, the pathogen could be killed, for example, by using an antibiotic to destroy the disease-causing bac- teria. At link 2, one could eliminate a reservoir that harbors the pathogen. For example,controlling rat populations in cities by picking up garbage is a way of preventing the spread of plague to humans. Adequate water and sewage treatment prevents the spread of water-borne diseases, and proper food-handling methods eliminate reservoirs of food-borne pathogens. At link 3, transmission from one host to another could be prevented by quarantin- ing infected individuals, for example, or by warning people to boil their water if the water supply becomes contaminated. Hand washing is an important way to prevent the spread of disease: it prevents restaurant workers from contaminating food, hospital workers from carrying pathogens from one patient to another, and allows all individu- als to protect themselves against pathogens they may pick up from the environment and put in their mouth. The spread of sexually transmitted diseases can be prevented by use of a condom, a simple matter of blocking the movement of the pathogens to the uninfected person. At link 4, the resistance of hosts can be increased by immunization, which stimulates the body's immune system to recognize the pathogen and to attack it during any future exposure. Vaccination not only keeps the individual from contracting a disease but also makes it harder for the pathogen to find susceptible hosts. In some cases, it may even be possible to completely eliminate a pathogen from the earth by eliminating the susceptibility of its potential hosts. This was accomplished in the case of smallpox, as discussed below. Other links are often included separately as part of the chain of infection when it is useful to consider them as sites for public health intervention. For example, the port of entry into the host for a mosquito-borne disease would be the skin, a link that could be interrupted if the potential host wears long sleeves and gloves. Similarly, the place of exit is the route by which the pathogen leaves the host.

Public health measures to control the spread of infectious disease include both

Public health measures to control the spread of infectious disease include both routine prevention measures and emergency measures to control an outbreak once it has begun. Many of the measures referred to above—especially those concerning links 2 and 3— come under the category of "environmental health." Immunization—link 4—is a major weapon that has had great success against the dread diseases that created the epidemics of the past. However, vaccines do not exist for all diseases—notably, a vaccine has not yet been developed against AIDS. Even when vaccines do exist, some diseases are too rare to justify the trouble and expense of vaccinating everyone. This is where surveillance is especially important.

Public health's mission

Public health's mission is to prevent disease, while medicine traditionally focuses more on treatment and cure. However, the fact that the medical profession can—and often does—play an important role in communicating public health messages about healthy behavior means that public health has a role to play in educating medical providers about health risks and health-related behaviors.

controlling a disease: rabies

Rabies is an example of a disease that has been successfully controlled in the United States by public health measures. Immunization of dogs is the primary barrier protecting humans from the reservoir of the virus, which is wild animals. By maintaining surveillance and intervening with vaccination when a person has been exposed to a possibly rabid animal, public health has kept the number of human deaths from rabies very low. SARS,a new, highly communicable disease first recognized in Asia in 2003, was successfully controlled by the classic public health measures of surveillance, isolation, and quarantine.

Rabies Virus

Rabies, a fatal disease of the nervous system caused by a virus, kills an estimated 60,000 people around the world each year, usually contracted through a dog bite. In the United States, transmission of the disease to humans is very effectively prevented by routine pub- lic health measures. Although there is an effective human vaccine against rabies, routine immunization of everyone is not recommended. Human exposure to the rabies virus in this country is relatively rare, and the vaccine is expensive and inconvenient to deliver, requiring several injections over a period of approximately a month. The rabies virus infects only mammals, and it is almost always transmitted when a rabid animal bites another animal or a human. Since the animal most likely to bite a human is the dog, mandatory immunization of dogs against rabies is the first line of defense in the protection of people. Wild animals serve as the reservoir of rabies, and dogs are most likely to be exposed by being bitten by a rabid wild animal. Domestic cats are also at risk for exposure to rabies from wildlife, and immunization is recommended for them as well. The public health system has defined clear guidelines for responding to a report of a person's being bitten by a domestic or wild animal, depending on the likelihood that the animal is rabid. Because immunization of dogs is widespread in the United States, less than 100 cases of rabies occur annually in the 60 million dogs in this country, and a dog bite is considered unlikely to transmit the disease. If the biting dog (or cat) appears to be healthy, it need only be observed for 10 days to ensure that it remains healthy. Rabies virus affects the brain and from there travels to the salivary glands and is secreted in saliva.An animal capable of transmitting the virus in its saliva will already have brain involvement, exhibit symptoms, and be dead within a few days. That is sufficient time for the bitten person to be given the series of vaccinations that will protect him or her from the disease. If the biting animal is wild, or if there is other reason to suspect that it is rabid, it must be killed and its brain tested for signs of rabies virus infection. There is no way to determine definitively whether a living animal has rabies. If the test shows the animal to be rabid, the bite victim receives the vaccinations. If no sign of rabies is found, no vaccinations are given. There is no room for error in these tests, because once symptoms of rabies appear, it is too late to save the victim. Public health laboratories take this responsibility very seriously. Generally, immunizations are given to anyone who is bitten by a wild animal that cannot be captured and tested. To control rabies, public health practitioners conduct surveillance for rabies in wildlife. When raccoons, skunks, and foxes in a geographic area are infected with the virus, they are likely to be a threat to humans and domestic animals. In Europe and in some parts of the United States, public health officials are attempting to control rabies in wildlife by distributing bait containing an oral rabies vaccine. Bats are the most dangerous rabies threat to humans. Even in parts of the country where the disease is not endemic among most wildlife, rabid bats are likely to be found. Because the animals are nocturnal and elusive, contact with bats may go unnoticed. By the time the puppy was diagnosed, the animals had been dispersed to 16 states around the country. Concerned that the puppy might have bitten other animals in the group, federal and state public health workers tracked them all down, vaccinated them and placed them in quarantine for six months.11 As a result of this incident, the Centers for Disease Control and Prevention (CDC) issued new regulations on the importation of animals to the United States.12

Regulation Approach

Regulation is another effective approach to promoting behavioral change, although it is often unpopular. Historically, the most ambitious attempt to regulate Americans' behavior was Prohibition, which did in fact improve their health by reducing the rate of cirrhosis of the liver. Whether the Prohibition-like approach currently used for control of illegal drugs is effective has not been demonstrated.

Results from education

Results of efforts to modify dietary and smoking behaviors, while showing some success, also illustrate the limitations of the educational approach. The impact of both messages has been limited. While the percentage of Americans who smoke has declined, almost one in five adults maintains the habit despite widespread knowledge about the dangers of tobacco.8 Evidence of dietary improvement is difficult to verify, since surveys of people's eating habits are notoriously unreliable. While the decline in heart disease is encouraging, the prevalence of obesity has increased, casting doubt on the extent to which Americans have really improved their eating habits. Educational efforts to modify health-related behavior can be controversial, even when the messages seem benign and obvious. For decades the tobacco industry used all its political and economic power to dispute the evidence that smoking was harmful. Even the government's policy on diet has generated opposition, for example, from the meat industry, which has fought to delay the release of proposed recommendations that people eat less meat and more fruits, vegetables, and grains—recommendations that, if widely followed, would financially harm the industry.9 Similarly, the sugar industry has fought government recommendations that people should reduce sugar in the diet.10 The educational messages most guaranteed to generate controversy, however, are those concerning sexual behavior. American attitudes about sex are notoriously ambiva- lent. Though movies and television shows frankly depict sexual activity, many people are puritanically reluctant to talk about how people can protect themselves against the natural consequences of that activity: unintended pregnancy and sexually transmitted diseases. For example, the tenure of Joycelyn Elders as President Clinton's Surgeon General was extremely controversial because she spoke out openly on these issues, recommending condom use and masturbation, until she was forced by political pres- sures to resign her office. Schools are naturally a prime site for health education programs. The goal is to teach children from an early age how to live healthy lives, providing information, for example, on diet, exercise, and the dangers of smoking, alcohol use, and drug abuse. Studies have shown that school education programs are effective in teaching children the facts about health and safety. It is less clear, however, that they actually influence young people to behave in healthier ways. Sex education in the schools is highly controversial. Opponents have argued for years that teaching young people about sex encourages them to indulge in immoral behavior. When AIDS came along, the controversy became more intense because it meant that sexual behavior could be a matter of life and death. Many proponents of explicit education about safe sex argue that young people have sex no matter what they are taught and that they should be informed about how to protect themselves. Opponents argue that condoms are only partially effective in preventing pregnancy and sexually transmitted diseases and that young people should be taught that they can protect themselves only by abstinence. This was the policy of the George W. Bush administration, which allocated hundreds of millions of dollars of federal funds for abstinence-only education. Many of these programs commonly contained multiple scientific and medical inaccuracies. According to Richard Daines, the New York State Commissioner of Health, "the Bush administration's abstinence-only program is an example of a failed national health-care policy directive, based on ideology rather than on sound scientific evidence that must be the cornerstone of good public health-care policy."11 In fact, a number of studies have shown that students who have received compre- hensive sex education in school delay initiation of sex, reduce the number of partners, and are more likely to use contraception when they do have sex. And while the use of condoms cannot guarantee protection against pregnancy and HIV transmission, con- doms do reduce risk. Nevertheless, the controversy continues in many communities. The decision on what students should be taught about sex is made by local school boards and depends on "community standards."

Technique to classify bacteria

Robert Koch, a German physician, developed techniques to classify bacteria by their shape and their propensity to be stained by various dyes. Theserules,called"Koch'spostulates,"are(1)theorgan- ism must be present in every case of the disease; (2) the organism must be isolated and grown in the laboratory; (3) when injected with the laboratory-grown culture, susceptible test animals must develop the disease; and (4) the organism must be isolated from the newly infected animals and the process repeated. Koch applied these rules in his proof that tubercle bacilli were the cause of tuber- culosis, the leading cause of death in Europe at that time. Bacilli are bacteria that appear rod-shaped when observed under the microscope. Koch identified another bacillus, Vibrio cholera, as the cause of cholera. Other disease-causing bacilli identi- fied during that period were those that cause plague, typhoid, tetanus, diphtheria, and dysentery. Round-shaped bacteria, called cocci, include streptococci, which cause strep throat and scarlet fever; staphylococci, which cause wound infections; and pneumococci, which cause pneumonia. Syphilis is caused by a corkscrew-shaped bacterium called a spirochete. All these bacteria were identified by the beginning of the 20th century.

nonhuman reservoirs

Smallpox, measles, and polio are viral diseases against which effective vaccines have been developed and which have no nonhuman reservoir. In theory, therefore, they could be eliminated from the earth. This has been accomplished with smallpox, with only two known stocks of the virus remaining. Polio has been eliminated from the United States and many other parts of the world, and a campaign is underway to eradicate it, although progress has been erratic and some experts doubt that the goal is realistic. The prospects for measles eradi- cation are even less clear. The United States has had periodic epidemics of measles, including one in 2014-2015, that occur when infected people enter this country from endemic areas. Reluctance by some parents to vaccinate their children weakens herd immunity and threatens to cause outbreaks of infectious diseases that could have been controlled.

Human behavior is strongly affected by

Social environment This accounts, at least in part, for the fact that diseases tend to be distributed in the population according to certain patterns: Certain groups have characteristic disease patterns that remain constant over time even when individuals in the group change. From a public health perspective, it may be more efficient to try to change the social environment that influences people to behave in unhealthy ways than to try to change people's behavior one individual at a time. Another reason to consider the social environment in studying health behavior is that when the focus is on the individual, the conclusion is likely to be that the person is to blame for his or her illness. Unhealthy behaviors may be maintained and reinforced by aspects of the social environment that are beyond the individual's control. It may be more appropriate for public health intervention programs to focus on these social aspects or at least consider them in designing programs aimed at promoting healthy behavior.

Success in controlling infectious diseases

Success in controlling infectious diseases requires adequate resources and political will to maintain effective immunization programs and ongoing epidemiologic surveillance.

success of Aids prevention program

The San Francisco AIDS prevention program was highly successful. Surveys done between 1984 and 1988 found that gay men had dramatically reduced their high-risk sexual behaviors during that period. The early success of AIDS prevention programs among gay men, in the rest of the country as well as in San Francisco, was attributable largely to the fact that the gay community was in general well educated and politically astute. The epidemic's potential victims tended to be of high SES, motivated to preserve their health and able to mobilize resources to cope with the impending threat. Thus, they were more receptive to the health promotion campaign than other groups at risk for HIV. However, the success at reducing high-risk behavior has not been maintained. Ongoing studies of gay men in San Francisco found that the prevalence of unprotected anal intercourse had increased from 31 percent in 1998 to 46.6 percent in 2011.21,22 Despite continuing HIV prevention programs, the prevalence of HIV-positive status among gay men in San Francisco has stabilized at about 24 percent Public health workers attribute the resurgence of sexual risk behaviors to the advent of highly active antiretroviral therapy in 1995. Because of the remarkable effectiveness of the new drug treatments, many younger gay men saw HIV infection as a less severe threat (a factor in the health belief model) than did older gay men. The growing number of infected individuals, who are living longer because of therapy, and the persistence of unsafe sexual behaviors have led to a high rate of new infections, which more than replace the number of gay men who die from AIDS, which remains stable

Fear of vaccines

The benefits of vaccination are obvious to public health and medical professionals. How- ever, just as Muslim leaders in Nigeria resisted polio vaccination with the rumor of infertil- ity, so suspicion has spread in the United States that measles immunization causes autism. Autism often becomes apparent at about the age when the vaccine is given. Consequently, some parents refused to allow their children to be vaccinated against measles. Similarly, unfounded stories about side effects of the pertussis (whooping cough) vaccine—that it might cause sudden infant death syndrome (SIDS)—led many parents to resist that vaccine. The measles outbreaks in 2011 and 2014, discussed above, illustrate the dangers of leaving children unvaccinated. Most of the cases were linked to people who had traveled abroad or visited from another country and spread the virus to unvaccinated children in this country. It is often in wealthy communities that parents refuse to subject their chil- dren to the small risk of immunization. They count on the fact that most other children are vaccinated to protect their own children from being exposed. However, much of the protection afforded by a high rate of immunization in a population comes from "herd immunity,"the phenomenon by which even infants too young to be vaccinated and people with weakened immune systems for various reasons, as well as those who refuse to be immunized, are unlikely to be exposed to a disease because the majority of the population is immune. If the percentage of immunity in the population falls too low, however, outbreaks are likely. Then even vaccinated people are at risk, because no vaccine is perfect. In Orange County, California, where Disneyland is located, some private schools have immunization rates as low as 60 percent. Parents of children with cancer and other condi- tions that preclude vaccination are becoming increasingly angry at the risk their children are being exposed to as a result of other parents' refusal to vaccinate their children.32 The news about the Disneyland measles outbreak led California to put an end to the personal belief exemption in 2015.33 Another drawback of people's fear of vaccines is that pharmaceutical companies have become reluctant to invest in developing them. Parents' tendency to blame a recent immunization for any serious health problem suffered by their children leads them to sue the company that made the vaccine. This experience, together with the fact that prices that can be charged for vaccines tend to be low, has caused many companies to drop vaccine production altogether.While immunization is considered the most effective intervention for preventing disease and promoting health, it is not clear that even the current vaccines will continue to be available. The example of the former Soviet Union stands as a warning to us. Diphtheria is virtually unknown in the West now, but in the 1980s, when the public health system in Russia was in chaos and immunizations stopped, the disease surged, with 200,000 cases and 5000 deaths there.33

health belief model.

The classic frame of reference for understanding health behavior, and especially behavior change, is the health belief model. Assuming that people act in rational ways, the health belief model specifies several factors that determine whether a person is likely to change behavior when faced with a health threat. These factors are (1) the extent to which the individual feels vulnerable to the threat, (2) the perceived severity of the threat, (3) perceived barriers to taking action to reduce the risk, and (4) the perceived effectiveness of taking an action to prevent or minimize the problem. Based on the health belief model, the public health approach to changing behavior would be to convince people that they are vulnerable, that the threat is severe, and that certain actions are effective preventive measures. For example, surveys of low-income minority women who had not had mammograms found that many had misperceptions about the disease. Some women underestimated their susceptibility to breast cancer (factor 1); others were embarrassed or afraid of the pain or radiation involved in a mammogram (factor 3); and others felt that cancer was not curable and therefore there would be no point in diagnosing it early (factor 4). Screening rates among these women could be improved by counseling that included personally tailored messages that addressed the women's beliefs and concerns.13

The evidence indicates that health promotion programs are most effective when

The evidence indicates that health promotion programs are most effective when they target individuals at many different levels of influence.

first three elements of aids campaign

The first three elements of the campaign targeted individual health beliefs and self-efficacy. The fourth element addressed interpersonal and community influences. The campaign targeted community influences by providing educational programs for bartenders in establishments frequented by gay men. Condoms were made widely available in bars and small group meetings and were distributed by volunteers on street corners. The public policy, government level of influence was brought in through provision by the city of free, confidential testing for the human immunodeficiency virus (HIV) antibody. Because public bathhouses were a frequent site of high-risk behavior, there was pressure on the city government to close them, as was done in New York City. However, the campaign as a whole was so successful in changing the behavior of gay men that business at the bathhouses fell off, and public health officers were satisfied with merely posting warnings to the clientele about safe sex.19

The health belief model and the transtheoretical model

The health belief model and the transtheoretical model are not contradictory; they are merely alternative ways of looking at what may be the same psychological factors. Both models can be useful in designing public health messages aimed at changing behavior.

Human diseases

The human diseases caused by viruses include smallpox, yellow fever, polio, hepatitis, influenza, measles, rabies, and AIDS, as well as the common cold. Human diseases can also be caused by protozoa, or single-celled animals that can live as parasitesinthehumanbody.Malaria,spreadbymosquitoes;cryptospiridiosis,whichcaused the Milwaukee diarrhea epidemic described earlier in this text; and giardiasis, also known as "beaver fever" are examples of protozoal diseases. Other parasites, such as roundworms, tapeworms, hookworms, and pinworms, are the most common source of human infection in the world. Except for pinworms, they are not common in the United States today.

The fourth level: The larger community

The larger community—the fourth level—can be a significant influence on behavior. Organizations can work together in a community to jointly promote healthy goals. An understanding of community organization and networks can offer insight into promising avenues for health promotion. For example, churches are the social centers for many black and rural communities and may provide a focal point for health-related interventions. Conversely, community factors may sabotage public health efforts to promote healthy behavior. In the South, where tobacco is a pillar of local economies, public health advocates may find it difficult to even raise the issue of the health consequences of smoking.

The most effective public health intervention programs influence people's beliefs at

The most effective public health intervention programs influence people's beliefs at several levels with the goal of creating a social environment favorable to healthy behavior. The San Francisco AIDS prevention program is an example of an effective program that succeeded in significantly reducing the transmission of HIV early in the epidemic. Evidence shows, however, that in order to maintain the success of such a program, intensive public health efforts must be maintained, both to prevent relapses into unhealthy behavior and to educate new generations of at-risk people. Increasingly, public health advocates realize that the most effective ways of improving health-related behavior of individuals is to focus on involving whole communities in improving the social and physical environment to be more conducive to healthy behavior.

SES

The most important predictor of health is socioeconomic status (SES), a concept that includes income, education, and occupational status, factors that tend to be strongly associ- ated with each other. SES accounts in part, though not entirely, for the health differences by race, sex, and marital status. For example, blacks tend to be less healthy than whites, and they generally have lower SES than whites. However, even wealthy, educated blacks have higher mortality rates than whites of comparable SES.1 Groups with the lowest SES have the highest mortality rates, a fact that is true in many different countries and has been true for centuries, for reasons known and unknown.2 In London in 1665, the poor were more likely to die in the plague epidemic because of poor nutrition and sanitation and because they could not flee the city to escape infection as the wealthy did. In the United States today, the health of the poor is threatened by the adverse environmental conditions of the inner cities, such as lead paint and air pollution, crime, and violence. Poor people also have poorer nutrition, less access to medical care, and more psychological stress.

chain of infection method of transmission component

The pathogen must have a way to travel from one host to another, or from a reservoir to a new host. The flea is a vector for plague, transfer- ring the plague bacillus from rat to human by sucking it up when it bites the rat and then injecting it into a human host with a second bite. Food-borne diseases are transmitted when a person eats contaminated food; water-borne diseases are transmitted when someone drinks contaminated water. Many respiratory diseases are transmitted by aerosol. AIDS, syphilis, gonorrhea, and a number of other dis- eases are transmitted by sexual contact.

chain of infection reservoir component

The reservoir is a place where the pathogen lives and multiplies. Some pathogens spread directly from one human to another and have no other reservoir. Others, however, may infect nonhuman species, spreading from them to humans only occasionally. Plague, for example, is a disease of rodents that is transmitted to humans by the bite of a flea. Rats are the reservoir of plague. Raccoons and bats are reservoirs for rabies, which spreads to humans only through the bite of a rabid animal. Contaminated water or food may also serve as reservoirs for some human diseases.

The third level of influence

The third level of influence is significant because people spend one-third to one-half of their waking lives in institutional settings, especially schools and workplaces, which may have profound effects on their health and health-related behavior. In the workplace, employees may encounter hazardous chemicals or risks from injuries and accidents. Stress may be a problem. Alternatively, organizations may provide a corporate culture that supports positive behavior change. Workplace or school cafeterias may provide health-conscious menus; exercise facilities may be available and their use encouraged; smoking restrictions may prevail. Schools and workplaces provide ideal settings for public health intervention.

Theories of health behavior

Theories of health behavior include the health belief model and the theory of self- efficacy. Both theories focus on the individuals' attitudes and beliefs as determinants of their behavior. The transtheoretical model of stages of change can be used in health education programs to promote behavior change.A broader perspective is provided by the ecological model of health behavior. This model considers all the levels of influence that may affect the individual's attitudes and beliefs, including interpersonal relationships such as family and friends, institutional influence such as school and work, the larger community and its values and beliefs, and public policy including laws and regulations.

Factors that influence health

There is evidence that factors such as race, gender, marital status, and especially SES influence health, and the reasons for these differences are likely to be social. Life expectancy, infant mortality, and mortality rates from a variety of diseases vary profoundly among different racial and ethnic groups. Stress, which may be brought on by social factors, has an adverse effect on health for a number of reasons. Social support has been found to have a positive effect on health, probably in part by providing a buffer against stress. The health of black Americans tends to be poorer than that of the white majority. Health data on the population is usually analyzed by race and ethnicity, and public health efforts focus on understanding the disparities and trying to eliminate them.

Explanation of findings

They concluded that the differences could not be explained by illness-induced weight loss or residual confounding by smoking, and they reaffirmed the findings of the 2005 study.5 The evidence is still strong that excess weight increases risks for heart disease, diabetes, high blood pressure, and some kinds of cancer. One possible explanation for the findings is that medical care has become increasingly effective in preventing deaths from these diseases. Despite the controversy, public health professionals continue to regard excess weight and obesity as a major threat to people's health.

health promotion and disease prevention programs cannot be done once and for all.

They must be repeated for every generation and every new at-risk group.

leaded causes of death

They observed that the leading causes were not, in fact, root causes but were merely the diagnoses identified at the time of death. These diseases result from a combina- tion of inborn (largely genetic) and external factors. The panel of experts undertook to identify, where possible, the underlying causes of death from each of the leading diseases. They came up with a list of nongenetic factors that they called the leading actual causes of death.1 While the mortality figures were only estimates, they were based on the best data available. These factors are highly significant for public health because they are preventable causes of death and disability and because they provide targets for public health intervention. In 2000, CDC scientists repeated the analysis with new data and found some changes, although the order of importance is almost the same.2 (Table 13-3) shows the leading actual causes of death in 2000, which are still presented as valid on the CDC's website.3

Socioeconomic differences

Variable access to medical care is another factor that has been blamed for some of the socioeconomic differences in health. In the United States, where 15 percent to 20 percent of the population—mostly those in low socioeconomic groups—lacks health insurance, it was often argued that universal health insurance could reduce health inequalities. However, the SES differences in mortality are also seen in Britain, Scandinavian nations, and other countries that have national health programs. The British civil servants in the Whitehall Study all had the same medical coverage by the National Health Service; yet the mortality risks were still higher at lower employment grades, even when behavioral factors were taken into consideration.

Early successes of public health, in its mission to prevent death and disability

often came from focusing on specific diseases or groups of diseases, seeking particular causes, and finding ways to interrupt the cause-and-effect relationships. Public health professionals learned to break the chains of infection, most often by removing etiologic agents (bac- teria, viruses, parasites) from the environment (water, food) or by developing vaccines to immunize potential hosts.

means of transmission: time phase

ome diseases are most likely to be transmitted during the most symptomatic phase, for example, when a patient suffering from tuberculosis or the common cold is most actively coughing and sneezing. Others, such as measles and mumps, are most communicable during the day or two before noticeable symptoms develop.A few diseases can exist in a carrier state, in which the infected person can transmit the disease without having symptoms, as demonstrated by the infamous case of Typhoid Mary.

top three actual causes of death

re smoking, poor diet and physical inactivity, and alcohol consumption. Other behavioral factors that are among the top nine causes of death are firearms, sexual behavior, motor vehicles, and the illicit use of drugs. For public health to significantly reduce the death rates beyond what it can achieve in controlling infectious diseases, it must find ways to promote behavioral change.

Decline in infectious diseases

reported that death rates for 13 infectious diseases were at all-time lows; for nine of them, including whooping cough, polio, and diphthe- ria, deaths and hospitalizations declined by more than 90 percent since vaccines against them were approved.34 However, it has become clear that infectious diseases are far from being conquered. The development of resistance to the chemical arsenal for combating disease is discussed elsewhere together with other new and emerging problems in infec- tious diseases.

Smallpox

While constant vigilance is required to protect people from rabies because wild animals serve as a reservoir of the disease, some pathogenic viruses, including measles and polio, have no nonhuman reservoir. It is a possibility, therefore, that universal immunization against these diseases could eliminate the measles and polio viruses from the earth. This has been achieved with smallpox, one of public health's greatest victories. Smallpox was a particularly feared disease that is believed to have first emerged in Asia about the time of Christ and tended to spread in major epidemics that claimed mil- lions of lives in China, Japan, the Roman Empire, Europe, and the Americas.2 It was highly contagious, spread by aerosol or by touch. The concept of vaccination originated with smallpox: the observation that survivors of the disease were immune to future infection inspired the idea that people could be protected against serious illness by inoculating them with small amounts of infected matter from a person suffering a mild case.While the procedure was not entirely safe, the practice became widespread in the American colonies, and George Washington ordered his entire army to be inoculated. In 1796, the practice of immunization became less risky when the British physician Edward Jenner—inspired by the observation that milkmaids appeared to be immune to smallpox—proved that inoculation with cowpox matter, which was harmless to humans, provided immunity against smallpox.13 By 1958, routine immunization had eliminated smallpox in the United States and other industrialized countries. However, it was still widespread in 33 underdeveloped countries, killing two million people per year. With support from both the United States and the Soviet Union, WHO developed plans for a program to eliminate smallpox. Between 1967 and 1977, medical teams traveled all over the world in search of outbreaks of the disease. Local governments were mobilized to vaccinate residents of areas where an outbreak was occurring. Because the lesions of smallpox were so conspicuous, it was possible for the investigators to track outbreaks by showing pictures of victims and asking people if they knew of anyone with this disease. Once a patient was located, he or she could be quarantined and everyone in the vicinity vaccinated, sometimes by force. The last case was found in Somalia in October 1977.2 Now the smallpox virus officially remains in only two places, stored in laboratories at the CDC and in a Russian laboratory in Siberia. By international agreement, genetic studies were being conducted, after which both stocks of the virus were scheduled to be destroyed in 1999. The decision to destroy the virus was controversial, with some scientists believing that valuable information might be gained in future studies using techniques that werenotyetknown.In1999,WHOdecidedtodeferthedestructionforafewmoreyears.14 Meanwhile, word was leaking out of the former Soviet Union that the Soviets had been working on smallpox as a bioweapon. There were fears that they had shared their stocks of the virus with rogue states such as Iraq and North Korea. The anthrax attacks of 2001 further raised fears about bioterrorism. Plans for destruction of the smallpox virus were put on hold, and research priorities have focused on developing an improved vaccine and finding drugs that would be effective against the virus. As of 2014, the debate over smallpox virus destruction was still ongoing. Some scien- tists believe that valuable lessons remain to be learned by studying the virus. Others agree with D. A. Henderson, leader of the WHO's eradication effort, who says,"Let's destroy the virus and be done with it... We would be better off spending our money in better ways." One concern is that the molecular sequence of the virus is publicly known, meaning that, even if all smallpox viruses are eliminated, someone could synthesize it in a laboratory and loose it on the world.15

The major epidemic diseases are caused by....

bacteria, viruses, or parasites

There are two obvious approaches that the government has traditionally taken to promote healthy behavior:

education and regulation. Both of these approaches have had successes and both have had failures. Both continue to be important components of public health's struggle to accomplish its mission.

n trying to prevent premature death and disability, public health must focus on these nine factors.

two of them—microbial agents and toxic agents—have traditionally been public health issues. The other seven are rooted in the behavioral choices of individuals. This is the biggest challenge now faced by public health. How can people be persuaded to behave in healthier ways in a democratic society, where every step is fraught with political, economic, and moral controversy?

chain of infection suscepitible host component

ven if the pathogen gains entry, a new potential host may not be susceptible because the host has immunity to the pathogen. Immunity may develop as a result of previous exposure to the pathogen, or the host may naturally lack susceptibility for a variety of reasons. Most microorganisms are specifically adapted to infect certain species. Canine distemper virus, for example, does not infect humans. Even within species, susceptibility to specific viruses varies among individuals. Scientists have been puzzled why a very few people who have been repeatedly exposed to the human immunodeficiency virus (HIV) do not become infected; recent studies have found a genetic mutation that makes them resistant to the virus.

Application of the ecological model at the interpersonal level

would lead to differ- ent strategies in a teen drug prevention program depending on the nature of the teens' social relationships. A teen who belongs to a dense, homogeneous network will be more influenced by the norms and values of that group than a teen who relates individually to a number of separate individuals. In the close-knit group, drug prevention programs would have to focus on changing the norms about drug use within the existing network. When social networks are more loosely organized, the program might focus on creating drug-free networks, encouraging teens to associate with those networks, and reducing the desirability of membership in drug-using networks.

Focus on social and physical environment

to make it easier for people to behave in healthy ways. For example, there are many fewer deaths from motor vehicle crashes now than there were three decades ago. This public health success comes less from educational programs about safe driving than it does from safer design of highways and automobiles. Similarly, the San Francisco HIV researchers suggest that social biases against homosexuality may contribute to the AIDS epidemic. They propose that recognition of same-sex marriage might encourage more stable relationships among gays, reduce the number of sexual partners by each individual, and thereby reduce the individual's risk of being infected. Public policy affects risk of HIV infection among intravenous drug users by providing access to needle exchange programs, which are illegal in some communities. Environmental factors influence people's diet and activity patterns, which are the second most important factor in Americans' poor health. The government recommends that people eat five servings daily of fresh fruit and vegetables, but educating people who live in poor areas of the inner city will not help improve their diets if they do not have access to supermarkets or produce stands. Similarly, federal policies that since World War II have favored a suburban lifestyle must bear much of the blame for Americans' lack of exercise: People live in their cars because most places are not within walking distance. The environmental perspective forces people to think of public health problems as social and political issues that require collective action. Instead of blaming smokers for lack of will power, public opinion has shifted its focus to the tobacco industry and the enormous resources the industry has put into making their product attractive to young people, a way of thinking that has led to a remarkable change in public attitudes toward smoking. People take action, as black activists did against the alcoholic beverage industry when it began aggressively marketing high-powered malt liquors to young black males.24 This approach may lead to confrontations with very powerful economic interests, and it will not always be successful. However, when whole communities become involved, it has the potential of being the most effective way to bring about major changes in health and behavior.