Morbidity is the measure of illness in a population, and numbers and rates are calculated in a similar fashion as with incidence and prevalence. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. Greenwood M.Epidemics and crowd-diseases: an introduction to the study of epidemiology, Oxford University Press; 1935. Establishing a working case definition is the method by which public health officials define what individuals are included as official cases in the outbreak and illustrate the boundaries of the outbreak. 4) Temporality—The outcome must occur after the exposure. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences. 7) Coherence—Agreement between epidemiologic and laboratory findings increases the likelihood of a causal effect. Selection bias results from the identification of subjects/cases from a subset that is not representative of the entire population at risk. The answer is no, because of the difference between average and median. The case definition defines a case in terms of person, place, and time. In this scenario, the prevalence of coccidioidomycosis at the time of the serosurvey would be 237/6,821 or 0.035 (3.5%); the incidence in September would be 97 cases, and the incidence rate would be 97/6,821 or 0.014 (1.4%). Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. 2. They are relatively quick, easy, and inexpensive. 2) Consistency—Repeatedly similar findings observed by different persons in different places with different samples strengthen the likelihood of a causal effect. Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. We do not control or have responsibility for the content of any third-party site. In summary, descriptive epidemiology serves to describe the occurrence of disease in a population. In clinical medicine, two additional diagnostic test parameters are relevant. Therefore, studies are designed in ways that minimize the sources and effects of bias. This site complies with the HONcode standard for trustworthy health information: In epidemiology, variables are either associated or they are not. Type I error, also known as a false positive, is when the null hypothesis is rejected when it actually should have been accepted. That is why some investigators “match” cases and controls. Surgeon General’s now-standard warnings. What is important about your disease? It is the cornerstone of public health, and informs policy decisions and … 10.1: Principles of Epidemiology - Biology LibreTexts By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health. Summary. First, the measurement of many exposures is imprecise, especially of large groups in which the influence(s) of those exposures is difficult to define or not equally exerted. Observer bias: The investigator, having knowledge of the outcome(s), might record exposures differently between cases and controls. A rate is another type of ratio in which the denominator involves the passage of time. Although knowledge of the complete natural history is not absolutely necessary for treatment and control of disease in a population, it does facilitate the most effective interventions. Describe the distribution of health-related events in the population 3. Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Passive surveillance occurs when individual health care providers or diagnostic laboratories send periodic reports to the public health agency. Cates W. Epidemiology: Applying principles to clinical practice. Dictionary of epidemiology. Answer. epidemiology: The branch of a science dealing with the spread and control of diseases, computer viruses, concepts, etc., throughout populations or systems. Last JM, editor. The applications of epidemiology are diverse and include identifying causal mechanisms of disease, diagnostic testing, determining prognosis, and testing new treatments. Consider the relationship between animal bites and rabies; we know they are causally associated. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. Bias can be introduced in such a trial when either the participants or the investigator know which participants are in which group. The former is more subjective than the latter but can be just as effective, especially in field epidemiologic conditions. Describe clinical patterns 4. Graph the number of cases of congenital syphilis by year for the country, ____ 5. For example, establishing a working case definition typically begins while the diagnosis is in the process of being verified and continues through the initial process of systematic case finding. In other words, this is the error of accepting an alternative hypothesis (the real hypothesis of interest) when the results can actually be attributed to chance. Analytical studies are applied to study the etiology of disease, to identify a causal relationship between exposures and health outcomes. Finally, a pandemic occurs when an epidemic becomes global in scope (eg, influenza, HIV/AIDS). , DVM, MPH, DACVPM, Lincoln Memorial University; , DVM, MPVM, DACVPM, Department of Pathobiology, College of Veterinary Medicine, Auburn University. Infectious Disease Epidemiology. Researchers began the study in 1948 by recruiting 5,209 men and women, 30–62 yr old, from the town of Framingham, Massachusetts. The investigators jump back in time to identify a cohort of individuals at a point in time before they developed the outcomes of interest, and try to establish their exposure status at that point in time. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. ORs are calculated using a 2 × 2 frequency table ( Calculating an Odds Ratio. 4th ed. Further, at a single point in time (perhaps based on the results of a serosurvey of dogs in the practice area), 237 dogs of 6,821 dogs with active records in the practice had the disease. Concepts of Epidemiology: Integrating the Ideas, Theories, Principles and Methods of Epidemiology, 2nd Edition: By Raj Bhopal ISBN-10: 0-1995-4314-3, ISBN-13: 978-0-1995-4314-4, Oxford University Press, Inc. If so, they can analyze the exposure(s) that may have contributed to those outcomes. Recall bias: Cases and controls may remember an exposure differently (and non-randomly). How are they both important to public health? What is important about your disease? An epidemic occurs when a disease occurs in larger numbers than expected in a given population and geographic area. In medical research, these exposures typically include interventions such as vaccines, therapeutic drugs, surgical techniques, or medical devices. An attack rate is an incidence rate; however, the period of susceptibility is very short (usually confined to a single outbreak). 1. However, in some cases, the mere presence of the exposure, without regard to its magnitude, can trigger the effect. Why would it be important to find the right cause of the disease? Like the practice of medicine, the practice of epidemiology is both a science and an art. In the previous example, the incidence rate would be 13 cases per quarter/102 students, or 0.127 cases per quarter per student. In analytical studies, this conjecture is termed the null hypothesis, meaning that the default assumption is that there is no association between the exposure in question and the disease outcome. At its core, nutritional epidemiology seeks to understand the underlying biological basis of nutrition and the mechanisms by which diet can influence health. In this type of study, subjects are selected as either having a particular outcome (cases) or not having the outcome (controls). Those tests or diagnostic procedures known to produce the absolute best results are termed “gold standard” tests. Common person variables include age, sex, race, socioeconomic status, marital status, religion, smoker/nonsmoker, etc. Below are three key terms taken from the definition of epidemiology, followed by a list of activities that an epidemiologist might perform. Introduction Epidemiology is the study of epidemics and the epidemiologic method was initially used to investigate, control, and prevent epidemics of infectious disease. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. In this case, the peak of cases occur one incubation period after the exposure event. Identify risk factors for developing diseases 5. Consider a study comparing library usage between students at two universities. Therefore, the clinician and the epidemiologist have different responsibilities when faced with a person with illness. Common time variables include secular trends (changes over long periods of time), seasonal/cyclic periods, and specific points in time (eg, outbreaks, epidemics, clusters, etc). The results of interventional studies can be very powerful in proving causality or identifying efficacy of various interventions. What literature gaps is your study acknowledging (how is it unique?) A negative test result, therefore, strongly implies that disease is absent, whereas a positive result may require additional, confirmatory testing. Be the first to answer this question. Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Dr. Peter Davies of the Veterinary Manual Editorial Board discusses the importance of veterinarian... © 2020 Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, Epidemic curve common intermittent source, Calculating Test Sensitivity and Specificity. In addition to outbreaks having common sources, they can have propagated sources, in which cases can directly infect other cases separate from the initial source. 3. The proportion of female dogs among those found to have parasite infections would be 643/(889 + 643), or 0.42. A disease is considered endemic when it is constantly present within a given geographic area. Why would it be important to find the right cause of the disease? If the variables are associated, that relationship can be either positive or negative. The resulting rate allows epidemiologists to compare disease occurrence across different populations. Time: When and over what time period (hours, days, weeks, day vs night) does this disease occur? The 5 W’s are the essential components of a news story because if any of the five are missing, the story is incomplete. What is important about your exposure? Therefore, they are not independent. If the variables are not associated, there is no relationship; they are independent. In general, bias in descriptive studies is not as prevalent or significant as bias in analytical studies. One of the most famous medical prospective cohort studies is the Framingham Heart Study. Case reports are accounts of single or a few noteworthy health-related incidents (eg, an epidemiologic description of a case of human rabies). Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site, ____ 4. This could be stated as “Neutered male dogs would be nearly four times as likely as intact male dogs to develop prostate cancer.”. The natural history begins before infection (prepathogenesis period) when the agent simply exists in the environment, includes the factors that affect its incidence and distribution, and concludes with either its disappearance or persistence (endemnicity) in that environment. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.(2). Epidemiology is concerned with the frequency and pattern of health events in a population: Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population. Significant differences might result if students from one university were queried over the phone regarding library visits, whereas students at the other university were directly observed for actual usage. Epidemiology was originally focused exclusively on epidemics of communicable diseases (3) but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. In the case of animals, equivalent variables may include species, breed, reproductive status (eg, intact vs neutered, pregnant vs nonpregnant), function (eg, meat/milk/fiber production, race horse vs working horse vs pleasure horse, companion dog vs military working dog), and wild/feral vs domesticated (cats). One of the most basic ethical principles of medicine and epidemiology is the moral obligation to cause no harm to participants (non-malfeasance), whether physical or psychological. For example, when a patient with diarrheal disease presents, both are interested in establishing the correct diagnosis. Results showed that productivity increased during the course of the study regardless of the changes in light; the workers just performed better because of the attention. They are inherently retrospective, so they are relatively quick and inexpensive. Several sets of systematic criteria for determining causality have been proposed: 1) Strength—Although a small association does not mean that there is not a causal effect, the larger the association, the more likely that it is causal. In fact, in epidemiology, the term ratio is applied when the numerator is not a subset of the denominator. Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. image source: s-media-cache-ak0.pinimg.com There are a number of definitions of epidemiology described by different authors but the most suitable definition is that epidemiology may be defined as the detailed scientific study of the distribution and determinants of disease or disability in society. Chapter 2 (7 th ed) Principles of Epidemiology I. The other category of studies that comprise analytical epidemiology are interventional studies. Contemp Ob/Gyn 1982;20:147–61. When the period of the study is from the past to the present, the study is a retrospective cohort study. Although it did not prove causality alone, it was instrumental in the U.S. Start studying Chapter 5: Principles of Epidemiology. The negative predictive value (NPV) is the probability of a patient not having the disease condition when the test is negative. Relative risk is calculated by dividing the incidence rate of the disease or outcome in the exposed individuals by the incidence rate in the unexposed individuals. Epidemiology is applied in many areas of public health practice. Epidemiology is a population science that underpins health improvement and health care, and is concerned with the pattern, frequency, trends, and causes of disease. The numerator and denominator may be independent of each other. If two variables are positively associated, the values of both variables increase or decrease together. Place may also relate to risk of exposure to infectious animals at sale barns or during shipment or to external factors such as severe weather and natural disasters. The objectives of epidemiology include the following: to identify the etiology or cause of disease. In an example regarding the class of veterinary students, if 13 of them developed influenza over the course of 3 mo (one quarter), the incidence would be 13 cases per quarter. Two main types of bias in descriptive epidemiology are selection bias and observation bias. Focused studies can help assist epidemiologists to determine why those differences have occurred and to identify specific risk factors. Consider an example in which the incidence of prostate cancer among neutered male dogs was found to be 1.37%, and the incidence in intact male dogs was 0.36%. The positive predictive value (PPV) of a test is the probability of a patient actually having the disease condition when the test is positive. NPV is calculated as true negatives divided by the sum of the true negatives and the false negatives: d/(c + d). 1 2 3. Similarly, the epidemiologist uses the scientific methods of descriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community. It is usually associated with public health because it studies disease patterns and their impact… An RR of 1 means there is no difference in risk between the two groups. For this reason, it can be very difficult to legally use human participants in many such trials. to study the progression of disease. The unit under study is a group of people or animals versus an individual. As a discipline within public health, epidemiology includes the study of the frequency, patterns, and causes of health-related states or events in populations, and the application of the information gained to public health issues. Principles of Epidemiology Lecture 7. Key terms in this definition reflect some of the important principles of epidemiology. In the former, the investigator does not control the exposure between the groups under study and typically cannot randomly assign subjects to study groups. However, this is done judiciously, because changes to the case definition result in changes to the epidemic curve. PPV is calculated as true positives divided by the sum of the true positives and the false positives: a/(a + b). Case series are listings of a larger number of cases, usually presented consecutively (eg, a characterization of dog bite incidents in a population of veterinarians and/or technicians over time). Evaluate programs 10. PRINCIPLES OF EPIDEMIOLOGY. 3) Specificity—Causation is more likely in a very specific population at a specific site and disease with no other likely explanation. Epidemiology is a branch of research dedicated to understanding the causes and prevention of diseases. Confounding: In epidemiologic studies, a confounder is a variable that is not considered in the study design but is associated with the exposure and exerts an effect on the outcome. Epidemiology is concerned with the distribution and determinants of health and disease, morbidity, injury, disability, and mortality in populations. Rates are typically expressed as a measure of the frequency with which an event occurs in a defined population in a defined time (eg, the number of foodborne Salmonella infections per 100,000 people annually in the USA). The horizontal axis represents the date when an individual became ill, also called the date of onset. Because the cases have already been identified, they are appropriate for studying rare diseases and examining multiple exposures. False-negative test results do not affect the PPV. An OR >1 means the exposure is associated with a higher odds of the outcome, and an OR <1 means the exposure is associated with a lower odds of the outcome. Time variables are important to describe when disease occurs in relation to various factors of potential exposure and vulnerability. The Merck Veterinary Manual was first published in 1955 as a service to the community. This book, then, aims to explain the ideas underlying the language, principles, and basic methods in epidemiology. Innumerable factors influence the temporal waxing and waning of disease. As the investigation ensues and more information becomes available, it may be necessary to revise the case definition. The legacy of this great resource continues as the Merck Veterinary Manual in the US and Canada and the MSD Manual outside of North America. The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. Raccoon rabies was epidemic throughout the eastern USA for much of the 1980s and 1990s. However, while the clinician usually focuses on treating and caring for the individual, the epidemiologist focuses on identifying the exposure or source that caused the illness; the number of other persons who may have been similarly exposed; the potential for further spread in the community; and interventions to prevent additional cases or recurrences. Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. The epi curve is complex and may be limited by information deficiencies and inaccurate case definitions. Ideally, cases and controls should be as similar as possible in all characteristics except the outcome in order to make the comparisons simpler and more meaningful. A concept is an idea, but the word is usually reserved for complex, or interrelated, ideas. Principles of Epidemiology Public health workers use epidemiologic principles as the foundation for disease surveillance and investigation activities. 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