Tabulate the frequency of clinical signs, symptoms, and laboratory findings among children with chickenpox in Cincinnati, Ohio. Introduction Epidemiology is the study of epidemics and the epidemiologic method was initially used to investigate, control, and prevent epidemics of infectious disease. These are updated as new data come in and thus are subject to change. Public health surveillance is defined as the ongoing systematic collection, analysis, interpretation, and dissemination of outcome-specific data essential to the planning, implementation, and evaluation of public health practice. 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). The major advantage of the prospective cohort study is that many different exposures can be considered and analyzed for influencing the outcome under study. Answer. The negative predictive value (NPV) is the probability of a patient not having the disease condition when the test is negative. The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. Principles of Epidemiology Public health workers use epidemiologic principles as the foundation for disease surveillance and investigation activities. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences. Epidemiology is the study (scientific, systematic, data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (patient is community, individuals viewed collectively), and the application of (since epidemiology is a discipline within public health) this study to the control of health problems. They are typically used when insights of a particular health issue are available, commonly from previous descriptive studies. Bias can be introduced in such a trial when either the participants or the investigator know which participants are in which group. 5) Biological gradient—Greater exposure generally results in greater incidence of the outcome. Given the high specificity of confirmatory tests, a positive result strongly implies that disease is present. For animal populations, “place” may refer to housing (eg, indoors vs outdoors, pen number or stall) or type of herd management (eg, intensive feedlot confinement vs extensive grazing). The overall shape of the epi curve can give clues to the type of exposure that resulted in the outbreak. 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. 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). Active surveillance is usually much more expensive and labor intensive; it typically is limited to short-term analyses of high-impact events. Measures of disease frequency: definition and calculation of prevalence, incidence, risk, rate, basic and net reproductive rate, choosing suitable measures, limitations of case and population definitions and their impact on measures of disease frequency. 3 From this perspective, epidemiology has focused on how infectious disease is distributed in populations and the factors that determine this distribution. Among the most salient are to observe historical health trends to make useful projections into the future, discover (diagnose) current health and disease burden in a population, identify specific causes and risk factors of disease, differentiate between natural and intentional events (eg, bioterrorism), describe the natural history of a particular disease, compare various treatment and prevention products/techniques, assess the impact/efficiency/cost/outcome of interventions, prioritize intervention strategies, and provide foundation for public policy. Principles of Epidemiology Lecture 7. CDC twenty four seven. How are they both important to public health? Public health officials investigate disease outbreaks to control them, to prevent additional illnesses, and to learn how to prevent similar outbreaks from happening in the future. Case reports are accounts of single or a few noteworthy health-related incidents (eg, an epidemiologic description of a case of human rabies). In this type of study, participants are selected from a population and randomly assigned to one of two groups, one being the study group and the other being the control group. The case definition defines a case in terms of person, place, and time. They typically take less time and are less expensive. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. Pattern refers to the occurrence of health-related events by time, place, and person. Incidence is a measure of the new occurrence of a disease event (eg, illness or death) within a defined time period in a specified population. 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. Finally, they are useful in generating information about the overall context of health, especially how it is affected by variables such as demographics, geography, and the social environment. 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. In the former, the investigator does not control the exposure between the groups under study and typically cannot randomly assign subjects to study groups. Whether an outbreak is foodborne in origin or from another infectious source, the methodology is similar. Sensitivity is the probability of a positive test result when the disease is actually present. A subset of an epidemic is an outbreak, when the higher disease occurrence occurs in a smaller geographic area and shorter period of time. New York: Oxford University Press; 2001. p. 61. Time: When and over what time period (hours, days, weeks, day vs night) does this disease occur? PRINCIPLES OF EPIDEMIOLOGY. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. For example, in a class of veterinary students in which 88 are female and 14 are male, the sex ratio of female students to male students is 88/14, or 6.3 to 1. Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied. A rate is another type of ratio in which the denominator involves the passage of time. Back to top 10.1: Principles of Epidemiology Sensitivity and specificity are inversely proportional, ie, when one increases, the other decreases. In other words, there is an important characteristic of the controls that make them different from the general population. Case definitions are usually based on either clinical signs or diagnostic test results. In this case, the relative risk would be 1.37/0.36 or 3.8. In a propagated source outbreak, the peaks of cases occur one incubation period apart. What has the literature said about the exposure-disease relationship? Identify risk factors for developing diseases 5. What is important about your exposure? This is important in epidemiology, because rates can be used to measure the speed of a disease event or to make epidemiologic comparisons between populations over time. Disadvantages include a potentially high possibility of selection bias, the fact that individuals may have difficulty recalling certain exposures (termed recall bias), and the requirement for the existence of medical and/or exposure records. The other category of studies that comprise analytical epidemiology are interventional studies. A concept is the idea behind the word or phrase we use to describe something. A major advantage of randomized controlled clinical trials is an inherently high validity for identifying differences in therapeutic efficacy of various interventions. Mark on a map the residences of all children born with birth defects within 2 miles of a hazardous waste site, ____ 4. In another example, consider a large veterinary practice in the southwest USA that frequently sees dogs with coccidioidomycosis. As the investigation ensues and more information becomes available, it may be necessary to revise the case definition. It is against these gold standards that newer, usually faster and more convenient, tests are measured in terms of sensitivity and specificity. Start studying Chapter 5: Principles of Epidemiology. Place variables commonly illustrate geographic differences in the occurrence of a particular disease. Ecologic studies have several advantages over other types of observational studies. An epidemic occurs when a disease occurs in larger numbers than expected in a given population and geographic area. It provides the background for interventions to reduce transmission of infecting organisms, reduce the number of healthcare-associated infections, and protect healthcare providers from infection. Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events. The former is more subjective than the latter but can be just as effective, especially in field epidemiologic conditions. For example, in a common point source outbreak, the investigation frequently identifies the event (eg, meal, social gathering, etc) when the exposure occurred. In clinical medicine, two additional diagnostic test parameters are relevant. Common place variables include comparisons across national, state, and municipal boundaries and between urban and rural communities. 2. Although the communities may be selected at random, the individuals within them obviously are not. Place: Where does this disease occur? The unit under study is a group of people or animals versus an individual. 3. Although epidemiologists and direct health-care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.” The clinician is concerned about the health of an individual; the epidemiologist is concerned about the collective health of the people in a community or population. Merck & Co., Inc., Kenilworth, NJ, USA is a global healthcare leader working to help the world be well. An example is the healthy worker effect, which refers to the phenomenon that employed groups have lower mortality than the general population. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. Identify control and/or preventive measures 7. In this type of study, the units are groups (or communities) of participants assigned to treatment or control conditions. In evaluating the causality of disease associations, analytical studies address the question of “why” as opposed to the “person/place/time” of descriptive studies. Koch’s postulates are four criteria designed to establish a causal relationship between a causative microbe and a disease. 2. Describe the distribution of health-related events in the population 3. Graph the number of cases of congenital syphilis by year for the country, ____ 5. There are two broad types of epidemiological studies: 1. Epidemiology is concerned with the distribution and determinants of health and disease, morbidity, injury, disability, and mortality in populations. Researchers began the study in 1948 by recruiting 5,209 men and women, 30–62 yr old, from the town of Framingham, Massachusetts. Centers for Disease Control and Prevention. Perhaps the major disadvantage is the high potential for ethical implications if an intervention with great potential benefit is intentionally withheld from the control group (eg, the historic Tuskegee Syphilis Study). For veterinary epidemiology, this intervention is … Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. The answer is no, because of the difference between average and median. Describe clinical patterns 4. a = True positives; the test has correctly diagnosed the disease, b = False positives; the test is positive but disease is absent, c = False negatives; the test is negative but disease is present, d = true negatives; the test correctly diagnosed the absence of disease, Sensitivity is the true positives divided by the sum of the true positives and the false negatives: a/(a +c), Specificity is the true negatives divided by the sum of the true negatives and the false positives: d/(b + d). Although the risk in an epidemiological investigation is usually minimal, most people who take part gain no personal benefit. Observational studies – we do not interfere in the process of the disease, but simply observe the disease and the associated factors. Dona Schneider, PhD, MPH, FACE Concepts in Infectious Epidemiology. Distribution implies that diseases and other health outcomes do not occur randomly in populations; determinants are any factors that cause a change in a health condition or other defined characteristic; morbidity is illness due to a specific disease or health condition; mortality is death due to a specific disease or health condition; and the population at risk can be people, animals, or plants. Identify at least two different data sources relevant to your profile. Usually, cases remember exposures more clearly than controls. In epidemiology, variables are either associated or they are not. When the period of the study is from the present into the future, the study is a prospective cohort study. In other words, the study did not have adequate power to detect an association between a variable and an outcome when the association actually existed. False-negative test results do not affect the PPV. 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. Therefore, if the PPV of a test is 100%, the validity of a negative test result is still unknown. When the study ended, productivity went back to prestudy levels. 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. Person criteria typically include vulnerability factors such as age, sex, signs/symptoms, or attendance at certain meals or public functions. An attack rate is an incidence rate; however, the period of susceptibility is very short (usually confined to a single outbreak). When analyzing results of an epidemiologic study, there are two categorical types of error when either accepting or rejecting the null hypothesis. 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. Conversely, an RR >1 means the outcome is more likely to occur in the exposed group than in the unexposed group. Principles of Epidemiology Scope of epidemiology: definition, descriptive and analytical epidemiology, contribution to population health. In summary, descriptive epidemiology serves to describe the occurrence of disease in a population. Note that this assumption of no association is made even though the epidemiologist often thinks that some association actually exists. 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. These studies are commonly undertaken to assess the quality and effectiveness of educational programs, behavioral changes, or mass interventions such as water fluoridation. Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Learn vocabulary, terms, and more with flashcards, games, and other study tools. This course [book] was developed by the Centers for Disease Control and Prevention (CDC) as a self-study course. They are then compared in a retrospective way to identify differences in their exposures that might explain the differences in outcomes. Additionally, their application is limited to the study of one outcome. Be the first to answer! Recall bias: Cases and controls may remember an exposure differently (and non-randomly). • Epidemiology is scientific discipline of public health to study diseases in the community to acquire knowledge for health care of the society. Count health-related events 2. Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website. Descriptive methods are commonly applied to little-known diseases; they use preexisting data, address the questions of who/where/when, and identify potential associations for more in-depth analytical studies. Type I error, also known as a false positive, is when the null hypothesis is rejected when it actually should have been accepted. 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 a branch of research dedicated to understanding the causes and prevention of diseases. For diseases of high prevalence, the PPV of a test will be high and the NPV will be low. In other words, the word epidemiology has its roots in the study of what befalls a population. What has the literature said about the exposure-disease relationship? 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. NPV is calculated as true negatives divided by the sum of the true negatives and the false negatives: d/(c + d). Although a higher OR indicates a stronger association between exposure and outcome, it does not necessarily imply statistical significance and, by itself, is not enough to prove causality. Discuss data from these sources and their relation to the issue or community. In descriptive epidemiology, diseases are classified according to the variables of person, place, and time. 4) Temporality—The outcome must occur after the exposure. The purpose is to describe and identify opportunities for intervention. An example of the former was a spurious conclusion drawn from a study of the relationship between alcohol consumption and heart disease. That is why some investigators “match” cases and controls. The applications of epidemiology are diverse and include identifying causal mechanisms of disease, diagnostic testing, determining prognosis, and testing new treatments. An effective case definition is critical because it may be confusing, especially in the absence of definitive diagnostics, to differentiate between actual disease cases and those ill from other causes. The difference is that epidemiologists tend to use synonyms for the 5 W’s: diagnosis or health event (what), person (who), place (where), time (when), and causes, risk factors, and modes of transmission (why/how). What are the gaps? For veterinary epidemiology, this intervention is to enhance not only health but also productivity. You should match only one term per activity. 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. We do not control or have responsibility for the content of any third-party site. 1. Incidence rates are usually expressed by a multiplier that makes the number easier to conceptualize and compare. 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%. What is important about your exposure? In animals, time may refer to milking shift, breeding season, lambing/calving season, at weaning, during shipment, on arrival at the feedlot, dry vs wet season, etc. The same is true in characterizing epidemiologic events, whether it be an outbreak of norovirus among cruise ship passengers or the use of mammograms to detect early breast cancer. Epidemiology is the study of the patterns, causes, and effects of health and disease conditions in defined populations. Cates W. Epidemiology: Applying principles to clinical practice. That is, no test can eliminate the potential for false-positive and false-negative results. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. 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. For instance, animal rabies is endemic in the USA. 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. When corrected for the effects of this confounder, no association was found between alcohol consumption and heart disease. 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. To calculate the sensitivity and specificity of a test, consider the following 2 × 2 table (see Table: Calculating Test Sensitivity and Specificity). If the variables are associated, that relationship can be either positive or negative. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures. It is the cornerstone of public health, and informs policy decisions and … 10.1: Principles of Epidemiology - Biology LibreTexts Additionally, they can address rare outcomes, because the cases are selected after having already developed the disease or outcome. Passive surveillance is useful for longterm trend analysis (if reporting criteria remain consistent) and is much less expensive than active surveillance. The practice diagnosed 542 clinical cases in a particular year, 83 of which died from the disease in the course of that year. For example, when a patient with diarrheal disease presents, both are interested in establishing the correct diagnosis. Type II error, also known as a false negative, is when the null hypothesis is accepted when it actually should have been rejected. In contrast to observational studies, the investigator using an interventional approach can intentionally change some form of exposure between several groups to determine differences in outcome(s). ORs are calculated using a 2 × 2 frequency table ( Calculating an Odds Ratio. Therefore, the clinician and the epidemiologist have different responsibilities when faced with a person with illness. What are the principles of epidemiology? A nonmedical example of selection bias would occur in a voter survey, intended to predict the outcome of a political election, but drawn from a sample of voters from either high- or low-income status, neither of which would be representative of the overall voting population. 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). Principles of EPIDEMIOLOGY Second Edition An Introduction to Applied Epidemiology and Biostatistics 12/92 U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service Centers for Disease Control and Prevention (CDC) Epidemiology Program Office Public Health Practice Program Office Atlanta, Georgia 30333 Principles of Epidemiology: A Self-Teaching Guide consists of a series of problem-solving exercises designed to introduce and guide readers toward an understanding of the principles and methods of epidemiology, rather than the epidemiology of specific diseases or subject areas such as ""infectious disease"" or ""chronic disease"" epidemiology. 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. Chapter 2 (7 th ed) Principles of Epidemiology I. In fact, in epidemiology, the term ratio is applied when the numerator is not a subset of the denominator. Therefore, if a test was reported to have an NPV of 100%, the validity of a positive test result is still unknown. Analytical epidemiology is accomplished through either observational studies or interventional studies. PPV and NPV are clinically relevant, because they are directly related to the prevalence of disease. Key terms in this definition reflect some of the important principles of epidemiology. Compare food histories between persons with, ____ 2. When two variables are associated, it is sometimes obvious as to whether it is causal. In the latter case, cause-specific mortality is expressed as the case fatality rate (CFR), which is the number of deaths due to a particular disease occurring among individuals afflicted with that disease in a given time period. Cross-sectional studies are one-time assessments of the incidence or prevalence of a disease in a defined population, which is usually selected at random from a larger population at risk (eg, a serosurvey of veterinarians for the presence of antibodies to Bartonella henselae organisms to determine risk factors and for cat scratch disease). What is important about your disease? It is a cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. The trusted provider of veterinary information since 1955, Role of the Veterinarian in Public Health/One Health, Significant National Public Health Achievements, Incidence and Impact of Foodborne Diseases, Role of Food Animal Veterinarians in Control of Foodborne Pathogens. Risk factors group has no size limitation but must be taken into account interpreting. 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