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46347_CH03_4849.qxd 9/11/07 12:43 PM Page 62 © Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION Chapter 3 Epidemiology: The Study of Disease, Injury, and Death in the Community Chapter Outline Chapter Objectives Scenario After studying this chapter you will be able to: Introduction 1 Define the terms epidemic, epidemiology, and Definition of Epidemiology • History of Epidemiology epidemiologist, and explain their importance in community health. The Importance of Rates 2 List some diseases that caused epidemics in the Incidence, Prevalence, and Attack Rates • Crude and past and some that are causing epidemics today. Age-Adjusted Rates • Specific Rates 3 Discuss how the practice of epidemiology has Reporting of Births, Deaths, and Diseases changed since the days of Benjamin Rush and John Snow. Standardized Measurements of Health Status 4 Explain why rates are important in epidemiology of Populations and list some of the commonly used rates. Mortality Statistics • Life Expectancy • Years of Potential Life Lost • Disability-Adjusted Life Years 5 Define incidence and prevalence rates and provide • Health-Adjusted Life Expectancy examples of each. 6 Calculate a variety of rates from the appropriate Sources of Standardized Data data. The U.S. Census • Statistical Abstract of the United 7 Discuss the importance of disease reporting to a States • Monthly Vital Statistics Report • Morbidity community’s health and describe the reporting and Mortality Weekly Report • National Health process. Surveys 8 Define the following standardized measurements Epidemiological Studies of health status—life expectancy, years of poten- Descriptive Studies • Analytic Studies tial life lost (YPLL), disability-adjusted life years (DALYs), and health-adjusted life expectancy Chapter Summary (HALE). Review Questions 9 Identify sources of standardized data used by epidemiologists, community health workers, and Scenario: Analysis and Response health officials and list the types of data available Activities from each source. 10 List and describe the various types of epidemiolog- Community Health on the Web ical studies and explain the purpose of each. References ᭜ 62 ᭜ 46347_CH03_4849.qxd 9/11/07 12:43 PM Page 63 © Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION CHAPTER 3EPIDEMIOLOGY: THE STUDY OF DISEASE, INJURY, AND DEATH IN THE COMMUNITY ᭜ 63 SCENARIO John thought about this afternoon’s picnic. Everyone called Michael back to tell him that he had decided to go had a blast. For a while it had seemed almost too warm, to the campus health center. but plenty of cold drinks were available, and by late Elsewhere . afternoon it had become quite pleasant. The games were This had turned out to be an interesting volunteer expe- fun too . frisbee, soccer, softball, and volleyball. Then rience. As a requirement for her community health class, there was the picnic itself—turkey, potato salad, bread Kim had agreed to volunteer at the local health department. and butter, milk, and dessert—served about noon. The spring semester was almost over now, and she was It was now 8 P.M. that same night, and instead of writing a final report of her activities. During the term, she studying as he had planned, John was lying on his bed had spent her Friday afternoons accompanying a sanitarian with a bad stomachache. He was experiencing severe on his inspections of restaurants and retail food stores. She diarrhea and had made several hurried trips to the bath- also had helped him complete his reports on substandard room in the last half-hour. housing and malfunctioning septic tanks. The telephone rang, and it was Michael, John’s Dr. Turner, the health officer, had given Kim permis- roommate. He had gone to his girlfriend’s house after sion to use one of the department’s personal computers the picnic to work on a class project with her. He and for preparing her final report. Because it was Sunday Caroline were both sick with stomach cramps and diar- evening, she was alone in the health department office rhea, and Michael was calling to ask whether John was when the telephone rang. She briefly considered not sick too. As John was answering, he realized that he answering it but finally picked up the receiver. It was needed to run to the bathroom again. He quickly hung Dr. Lee from the University Health Center. He said he up, promising to call back soon. Moments later as he was calling in the hope that someone might be there returned to his bedroom, John began to think about because he needed to reach Dr. Turner immediately. He what a coincidence it was that all three of them were said that he had admitted six students to the infirmary sick with the same symptoms at about the same time. with severe stomach cramps, vomiting, and diarrhea. Could they have become ill from food they ate at the The students had been at a picnic earlier, and he picnic? There were about 50 people at the picnic; How thought they could have food poisoning. He called to many others might also be sick? Was it the heat? Was it ask Dr. Turner to investigate this outbreak and asked the food? Was this an epidemic? A half-hour later, John Kim to try to reach him as soon as possible. INTRODUCTION When you become ill and visit a doctor, the first thing the physician does is take measurements and collect information. The measurements include your temperature, heart rate, and blood pressure. The information includes time of onset of your illness, where you have traveled, and what you might have eaten. Next, you may be given a physical examination and asked to provide a specimen such as urine or blood for laboratory examination. The information gathered helps the physician understand the nature of your illness and prescribe an appropriate treatment. While a primary care physician is concerned with the course of disease in an individual patient, an epidemiologist is concerned with the course of disease in a population. When ill- ness, injury, or death occur at unexpected or unacceptable levels in a community or popula- tion, epidemiologists seek to collect information about the disease status of the community. First, epidemiologists want to know how many people are sick. Second, they want to know who is sick—the old? the young? males? females? rich? poor? They also want to know when the people became sick, and finally, where the sick people live or have traveled. In summary, epidemiologists want to know what it is that the sick people have in common. For this reason, epidemiology is sometimes referred to as population medicine. 46347_CH03_4849.qxd 9/11/07 12:43 PM Page 64 © Jones and Bartlett Publishers. NOT FOR SALE OR DISTRIBUTION 64 ᭜ UNIT ONE FOUNDATIONS OF COMMUNITY HEALTH Epidemiology is one of the community health activities “aimed at protecting or improving epidemiology the health of a population or community” discussed in Chapter 1. Information gathered from the study of the epidemiological studies assists community decision makers to make the best use of the com- distribution and determinants of munity’s human and financial health resources. Data gathered at local, state, and national levels health-related states can be used not only to prevent disease outbreaks or control those that are in progress, but or events in specified also to assess whether an ongoing disease prevention program is effective. populations Definition of Epidemiology Before we discuss the types of questions an epidemiologist asks, we need to define the term epidemic epidemiology. Epidemiology is “the study of the distribution and determinants of health- an unexpectedly related states or events in specified populations, and the application of this study to control large number of cases health problems.”1 The term epidemiology is derived from Greek words that can be translated of an illness, specific health-related into the phrase “the study of that which is upon the people.” The goal of epidemiology is to behavior, or other limit disease, injury, and death in a community by intervening to prevent or limit outbreaks or health-related event in a particular epidemics of disease and injury. This is accomplished by describing outbreaks and designing population studies to analyze them and to validate new approaches to prevention, control, and treatment. Through these practices, epidemiologists contribute to our knowledge of how diseases begin and spread through populations, and how they can be prevented, controlled, and treated. The question might be asked, how many cases are required before a disease outbreak is endemic disease considered an epidemic—10 cases? 100 cases? 1,000 cases? The answer is that it depends a disease that occurs upon the disease and the population, but any unexpectedly large number of cases of an ill- regularly in a population as a ness, specific health-related behavior, or other health-related event in a particular population matter of course at a particular time and place can be considered an epidemic. Some recent epidemics in the United States are presented in Table 3.1. The question might be asked, what are diseases called that occur regularly in a population but are not epidemic? These diseases are referred to as endemic diseases. Whether a disease epidemiologist is epidemic or endemic depends on the disease and the population. Heart disease is endemic one who practices in America, while in many regions of equatorial Africa, malaria is endemic. epidemiology An epidemiologist is “an investigator who studies the occurrence of disease or other health-related conditions or events in defined populations.”1 Some epidemics begin as out- breaks of disease in animals, known as epizootics, and then spread to human populations. Examples are bubonic plague that first affects rodents, and West Nile fever virus that first pandemic affects birds. Occasionally, an epidemic will spread over a wide area, perhaps even across an an outbreak of disease over a wide entire continent or around the world.

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