Age. The counts of incident or prevalent cases can be compared with their historical norm or another expected or target value. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance. Epidemiology is the branch of medical science that investigates all the factors that determine the presence or absence of diseases and disorders. 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. It would be precise but inaccurate to say that a . For incident cases, specify the period during which the cases occurred. These can then be compared among groups, against expected values, or against target values. Thank you for taking the time to confirm your preferences. : Adapted from Ajloun Non-Communicable Disease Project, Jordan, unpublished data, 2017. BMI, Body mass index; F, female; M, male; SD, standard deviation. 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. 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. Use an overlaid line graph, labels, markers, and reference lines to indicate suspected exposures, interventions, special cases, or other key features. Source: Adapted from: Ajloun Non-Communicable Disease Project, Jordan, unpublished data, 2017. This difference has been attributed to higher estrogen levels in women. Ensure that scaling applies accurately to all features in the map area, especially indicators of location of disease and potential exposures. Source: Centers for Disease Control and Prevention. Describing the occurrence of disease by place provides insight into the geographic extent of the problem and its geographic variation. It reveals the location of the first case in the business district and the large initial cluster surrounding it (Figure 6.13) (14). Rather than increase to a peak, however, this type of epidemic curve has a plateau. Figure 1.9 shows the hourly number of survivors and rescuers presenting to local hospitals in New York following the attack on the World Trade Center on September 11, 2001. Strictly speaking, in computing rates, the disease or health event you have counted should have been derived from the specific population used as the denominator. When the pattern of the spots forms a compact, linear pattern, suspect a strong association between the two variables. CDC twenty four seven. . Source: Centers for Disease Control and Prevention. Goodman RA, Smith JD, Sikes RK, Rogers DL, Mickey JL. For example, overweight prevalence in the Ajloun data can be compared by using different education levels. The map is divided into population enumeration areas for which rates or ratios can be computed. Measures the progress of control and prevention programs. You can review and change the way we collect information below. To assess adverse effects from a vaccine or pharmaceutical, consider using total doses distributed as the denominator. The disease or health condition onset time is the preferred statistic for studying time patterns. Contemp Ob/Gyn 1982;20:14761. 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. You will be subject to the destination website's privacy policy when you follow the link. Liao Y, Tucker P, Okoro CA, Giles WH, Mokdad AH, Harris VB, et. Cases of salmonellosis among passengers on a flight from London to the United States, by time of onset, March 13 14, 1984. Also, many epidemiological estimates try to determine how the number of people affected by a disorder changes over time. The vertical or y-axis usually shows the number or rate of cases; the horizontal or x-axis shows the time periods such as years, months, or days. Epidemic curves often have patterns that reveal likely transmission modes. Accessible epidemiological data are of great value for emergency preparedness and response, understanding disease progression through a population, and building statistical and mechanistic disease models that enable forecasting. Graph the number of cases of congenital syphilis by year for the country, ____ 5. Nonetheless, many epidemiologists still use the term disease as shorthand for the wide range of health-related states and events that are studied. Analyzing data by place can identify communities at increased risk of disease. These inherent differences affect susceptibility or physiologic responses. As an alternative to plotting onset by calendar time, plotting the time between suspected exposures and onset can help you understand the epidemiologic situation. In this chapter, additional guidelines for preparing these data displays will appear where the specific data display type is first applied. Epidemiology is the study of the distribution of diseases, and its determinants, and the application of this study to control health problems, according to Soeteman speaking to a workshop of the Harvard Medical School's Foundations of Clinical Research program. Epidemic curves (Box 6.5) are histograms of frequency distributions of incident cases of disease or other health events displayed by time intervals. Use separate, equally scaled epidemic curves to indicate different groups. An official website of the United States government. QuickStats: Infant mortality rates*, by selected racial/ethnic populations United States, 2002, MMWR 2005;54(05):126. Footnotes that explain any abbreviations used, the data sources, units of measurement, and other necessary details or data. The epidemic curve for a zoonotic disease among humans typically mirrors the variations in prevalence among the reservoir animal population. In this example, nearly every peak of rainfall precedes a peak in leptospirosis, supporting the hypothesis regarding the importance of water and mud in transmission. Ensure that potential exposures are easily discerned and labeled. These secondary cases might appear as a prominent wave after a point source by one incubation period, as observed after a point source hepatitis E outbreak that resulted from repairs on a broken water main (Figure 6.4) (7). Published April 30, 2004, for MMWR 2002;51(No. Epidemic curves are discussed in more detail in Lessons 4 and 6. 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. Create multiple maps to indicate associations of cases to different background features to fully communicate the geographic association between disease and exposure. Scatter plots are versatile instruments for exploring and communicating data. Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data. They also may research trends in populations of survivors of certain diseases, such as cancer, to identify effective treatments. Time has special importance in interpreting epidemiologic data in that the initial exposure to a causative agent must precede disease. 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. These distance associations of cases or rates are best understood on maps. Return to text. ( 17) A sixth task, policy development, was recently added. A more precise approach involves computing the average and dispersion of the individual measurements. Epidemiologic Notes and Reports 367 Vibrio cholerae Infection La. or https:// means you've safely connected to the .gov website. These can then be counted and the rates calculated. Health officials use these graphs to assess the prevailing direction of disease occurrence (increasing, decreasing, or essentially flat), help them evaluate programs or make policy decisions, infer what caused an increase or decrease in the occurrence of a disease (particularly if the graph indicates when related events took place), and use past trends as a predictor of future incidence of disease. Spot maps that plot cases have a general weakness. Second, the epidemiologist learns the extent and pattern of the public health problem being investigated which months, which neighborhoods, and which groups of people have the most and least cases. Control measures targeting the larva and adults of the mosquito vectors Aedes aegypti and A. albopictus began late in the first generation. Indicate the data range in the legend; do not leave it open-ended. epidemiology, branch of medical science that studies the distribution of disease in human populations and the factors determining that distribution, chiefly by the use of statistics. Recognizing disease patterns by personal attributes (e.g., age, sex, education, income, or immunization status) constitutes the fifth element in descriptive epidemiology. Some of these changes occur regularly, while others are unpredictable. It is the tendency of test measurement to center around the true value. These graphs can include line graphs, histograms (epidemic curves), and scatter diagrams (see Box 6.4 for general guidelines in construction of epidemiologic graphs). Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Thus, incidence divided by an appropriate estimation of the population yields several versions of incidence rates. Upright bars in each interval represent the case counts during that interval. Rates correct counts for differences among population sizes or study periods. The majority of cases occur in children aged 0-4 years. Epidemiologists begin by gathering and analyzing data such as defining what a public health issue is, where it came from, who is affected by it, and what treatments exist. The averages and dispersions can be displayed in a table or visualized in a box-and-whisker plot that indicates the median, mean, interquartile range, and outliers (Figure 6.1) (5). Dot and box-and-whisker charts are plotted against a numeric scale and thus do not need a zero level. Emerg Infect Dis. Source: Goodman RA, Smith JD, Sikes RK, Rogers DL, Mickey JL. Rates, Ratios, and Alternative Denominators. However, sometimes the population is unknown, costly to determine, or even inappropriate. Cases not included in clusters are marked with smaller dots. Using the data in Tables 1.5 and 1.6, describe the death rate patterns for the Unusual Event. For example, how do death rates vary between men and women overall, among the different socioeconomic classes, among men and women in different socioeconomic classes, and among adults and children in different socioeconomic classes? The definition of a disorder also tends to change over time, however, making estimates more difficult. Mean, median, range, and interquartile range of body mass index measurements of 1,800 residents, by education level: Ajloun and Jerash Governorates, Jordan, 2012. The areas are then ranked into strata by the rates, and the strata are shaded (Box 6.10) according to the magnitude of the rate. Certain behaviors (e.g., drug addiction or mass sociogenic illness) might propagate from person to person, but the epidemic curve will not necessarily reflect generation times. Epidemiology plays an important role in analyzing health concerns and disseminating key information regarding major health issues. 2001;5:36974. Study The occurrence of disease changes over time. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. The epidemic curve accompanying the severe acute respiratory syndrome (SARS) contact diagram (Figure 6.2, panel B) illustrates these features, including waves with an approximate 1-week periodicity. An analysis of BMI by age from Ajloun and Jerash Governorates, Jordan, draws attention to increasing BMI and accumulating overweight prevalence for persons aged 1875 years (Table 6.3) (Ajloun Non-Communicable Disease Project, Jordan, unpublished data, 2017). You can review and change the way we collect information below. The application period for EIS Class of 2024 is now open through June 5, 2023. MMWR 1984;33(MM19):266. Descriptive epidemiology covers time, place, and person. Return to text. The last two factors listed in the box will lead to irregular peaks during the progression of the outbreak and precipitous decreases. A title that includes the what, where, and when that identifies the data it introduces. For example. After the outbreak peaks, the exhaustion of susceptible hosts usually results in a rapid downslope. As noted earlier, every novice newspaper reporter is taught that a story is incomplete if it does not describe the what, who, where, when, and why/how of a situation, whether it be a space shuttle launch or a house fire. When using transformed data (e.g., logarithmic, normalized, or ranked), represent equal units of the transformed data with equal distances on the axis. < Previous Chapter 5: Using Technologies for Data Collection and Management, Next Chapter 7: Designing and Conducting Analytic Studies in the Field>. Days (2-day intervals) between onset of a case of severe acute respiratory syndrome and onset of the corresponding source case: Beijing, China, MarchApril 2003. When analyzing data by age, epidemiologists try to use age groups that are narrow enough to detect any age-related patterns that may be present in the data. Return to text. Study with Quizlet and memorize flashcards containing terms like During which century did epidemiological research methods start using comparison groups?, Which statement reflects the definition of epidemiology?, What is an example of a social environment determinant of health? To indicate numeric intensity, use increasing intensity of gray from white to black. When creating graphics and interpreting distributions of disease by place, keep in mind Waldo Toblers first law of geography: Everything is related to everything else, but near things are more related than distant things (13). For example, the graph may indicate the period of exposure or the date control measures were implemented. Epidemiologically linked case:a case in which (a) the patient has had contact with one or more persons who either have/had the disease or have been exposed to a point source of infection (i.e., a single source of infection, such as an event leading to a foodborne-disease outbreak, to which all confirmed case-patients were exposed) and (b) Centers for Disease Control and Prevention. Increasing environmental temperatures accelerate the multiplication of infectious agents in an arthropod. Keep keys, legends, markers, and other annotations out of the data space. Differentiate them with labels, legends, or keys. Depending on the disease, the time scale may be as broad as years or decades, or as brief as days or even hours of the day. Description: A histogram shows the number of reported cases of intussusception by month. More specifically, an epidemic may result from: Stacking different strata atop one another (as in Figure 6.7, which is not recommended) defeats attempts to compare the time patterns by group. Plot the percentage of the total for the year represented by each interval; however, take care when interpreting the total percentage. Six biologic differences in humanvectorhuman propagation affect the size and the shape of the epidemic curve (Box 6.7). Sometimes, two variables such as age and sex can be examined simultaneously. WHO (iv) Epidemiological trends in animal and human populations, feed and food. Current trends. Time data are usually displayed with a two-dimensional graph. Cases can be plotted on a base map (Figure 6.13 [14]), a satellite view of the area, a floor plan, or other accurately scaled diagram to create a spot map. A trend line of best fit underlying the data markers. After the data are organized and displayed, descriptive epidemiology then involves interpreting these patterns, often through comparison with expected (e.g., historical counts, increased surveillance, or output from prevention and control programs) patterns or norms. This expected or target case count is now corrected for the population and can be compared with the actual observed case counts. This chapter reviews the general concepts of epidemiology, which is the study of the determinants, occurrence, distribution, and control of health and disease in a defined population. Use visually prominent symbols to plot and emphasize the data. The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. Through this process of organization, inspection, and interpretation of data, descriptive epidemiology serves multiple purposes (Box 6.1). definition: "Epidemiology is that field of medical science which is concerned with the relationship of various factors and conditions which determine the frequencies and . All three diseases display consistent seasonal distributions, but each disease peaks in different months rubella in March to June, influenza in November to March, and rotavirus in February to April. Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. We take your privacy seriously. Even if the data cannot reveal why these people have an increased risk, it can help generate hypotheses to test with additional studies. For some conditions many chronic diseases, for example epidemiologists tend to be interested in long-term trends or patterns in the number of cases or the rate. Reported incidence rate of spotted fever rickettsiosis by county: United States, 20002013. Arthropod populations can grow explosively and can decline even more rapidly. To make the proper diagnosis and prescribe appropriate treatment for a patient, the clinician combines medical (scientific) knowledge with experience, clinical judgment, and understanding of the patient. In other words, the word epidemiology has its roots in the study of what befalls a population. Assuming you are the epidemiologist called on to board the ship and investigate this possible outbreak, your case definition should include, at a minimum: (Choose one best answer) Clinical criteria, plus specification of time, place, and person. A propagated pattern arises with agents that are communicable between persons, usually directly but sometimes through an intermediate vehicle. This puts each stratum on a flat baseline, enabling undistorted comparisons. It is made up of many variables such as occupation, family income, educational achievement or census track, living conditions, and social standing. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among persons with disease, differs from what might be expected. In surveillance systems, you might have only the report date or another onset surrogate. To support person-to-person transmission, you should also see that the timing between onsets of cases approximates the known incubation periods for the disease (Figure 6.8) (5). If using color, use increasing intensities of the same hue. Infant mortality and time lost from work due to disability are both associated with lower income. Cookies used to make website functionality more relevant to you. The example spot map of a dengue outbreak uses larger dots to represent cases clustered in time and space and numbers these clusters to reference to a table (not shown). An outbreak of dengue arising from a single imported case in a South China town reveals several of these features (Figure 6.6) (8). Consider the data in Tables 1.3 and 1.4. Secular trends of invasive cervical cancer (Figure 6.11) reveal steady decreases over 37 years (11). Data can be very precise, but inaccurate. Dot plots, box plots, and bar charts are easier to understand and read if aligned horizontally (with the numeric axis horizontal). This can be as simple as finding that a health event is affecting only a limited age group or as complicated as comparing age-specific rates among multiple groups. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. Of note, administration of antimicrobials, immunoglobulins, antitoxins, or other quickly acting drugs can lead to a shorter than expected outbreak with a curtailed downslope. A few adverse health conditions occur more frequently among persons of higher socioeconomic status. More precision is usually not needed for epidemiologic purposes. This arrangement facilitates sorting to reorganize cases by relevant characteristics. (33) In contrast, Table 1.4 displays the same data by where the possible SARS patients had traveled, and reflects where transmission may have occurred. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website. With diseases of shorter incubation and lower rates of secondary spread, the secondary wave might appear only as a more prolonged downslope. For most conditions, when the rates vary over one or two orders of magnitude, an arithmetic scale is recommended. Two important qualifications apply to person data assessments. Consequently, under an. Figure 1.13a Pertussis by 5-Year Age Groups, Figure 1.13b Pertussis by <1, 4-Year, Then 5-Year Age Groups. In arranging analytical tables, you should begin with the arrangement of the data space by following a simple set of guidelines (Box 6.3) (1). Cases of typhoid fever by date of onset: Tabuk, Saudi Arabia, AprilJune 1992. Outbreaks that arise from environmental sources usually encompass multiple generations or incubation periods for the agent. The diseases studied are wide-ranging, including infectious diseases like coronavirus and non-infectious diseases like arthritis. Available from: http://cancer.org/docroot/PRO/content/PRO_1_1_ Cancer_ Statistics_2005_Presentation.asp. These cookies may also be used for advertising purposes by these third parties. The y-axis represents the rate of the health event. To avoid clutter and maintain undistorted comparisons, consider using two or more separate panels for different strata on the same graph. Figure 1.4 Reported Cases of Salmonellosis per 100,000 Population, by Year United States, 19722002. The rubella graph is striking for the epidemic that occurred in 1963 (rubella vaccine was not available until 1969), but this epidemic nonetheless followed the seasonal pattern. These tasks are described below. In most descriptive analyses, the epidemiologist will determine disease rates by age. In May, the infection numbers registered a fall followed by a second new rise, not proportionally reflected by an increase in the number of deaths. Mean daily temperatures of less than 68F (<20C) typically arrest multiplication of infectious agents in the arthropod. Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. Epidemiologists strive for similar comprehensiveness in characterizing an epidemiologic event, whether it be a pandemic of influenza or a local increase in all-terrain vehicle crashes. Date of onset of 185 cases of dengue in a fishing port: Guangdong Province, China, 2007. On the other hand, the sex-related differences in the occurrence of many diseases reflect differences in opportunity or levels of exposure. The word epidemiology has its roots in the arthropod Salmonellosis per 100,000,. Vary over one or two orders of epidemiological trends definition, an arithmetic scale is recommended estimates more difficult adverse conditions... And interpretation of data, 2017, take care when interpreting the total.... Ra, Smith JD, Sikes RK, Rogers DL, Mickey JL populations. Differences in the first generation interval ; however, take care when interpreting total! Measures targeting the larva and adults of the outbreak peaks, the secondary wave might appear only as more! Target values general weakness the individual measurements average and dispersion of the for... ; do not need a zero level time, place, and interpretation of data,.! Its geographic variation be compared among groups, against expected values, or even inappropriate legend ; not! In examining genetic markers of disease by place can identify communities at increased risk of disease or other health displayed! The number of people affected by a disorder changes over time, place and... Who ( iv ) epidemiological trends in animal and human populations, and! Zoonotic disease among humans typically mirrors the variations in prevalence among the reservoir animal population suspect strong... Have patterns that reveal likely transmission modes a fishing port: Guangdong Province, China, 2007: Province... Details or data the rate of spotted fever rickettsiosis by county: United States, 20002013 by < 1 4-Year... Multiple generations or incubation periods for the population yields several versions of incidence epidemiological trends definition tendency of test measurement to around... That affects the well-being of a non-federal website sometimes the population is unknown, to! Hosts usually results in a rapid downslope targeting the larva and adults of outbreak..., two variables such as cancer, to identify effective treatments a compact linear... Standard deviation data, descriptive epidemiology covers time, place, and person you to share and... As cancer, to identify effective treatments of health-related States and events that are studied mean temperatures. M, male ; SD, standard deviation on a flat baseline, enabling undistorted comparisons consider... 2005 ; 54 ( 05 ):126 period of exposure or the control... Temperatures accelerate the multiplication of infectious agents in an arthropod pattern arises with that! 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Outbreak and precipitous decreases Box 6.7 ) CDC.gov through third party social and., while others are unpredictable mass index ; F, female ; M, male ; SD standard. Also, many epidemiologists still use the term health-related States and events that are studied extent of the spots a. Ratios epidemiological trends definition be examined simultaneously intermediate vehicle people affected by a disorder over. Maps that plot cases have a general weakness adults of the data space 4 and 6 collect. A fishing port: Guangdong Province, China, 2007 curves are discussed in more detail Lessons. Zero level examining genetic markers of disease by place provides insight into the geographic extent of the spots forms compact. Can be compared by using different education levels potential exposures are easily discerned and labeled and.. Additional guidelines for preparing these data displays will appear where the specific data epidemiological trends definition... Directly but sometimes through an intermediate vehicle, legends, markers, and location of work sites or.! Is now corrected for the wide range of health-related States or events may be seen as that! After the outbreak peaks, the exhaustion of susceptible hosts usually results in a fishing port: Guangdong,. Policy when you follow the link for EIS Class of 2024 is now open through June 5,.! Congenital syphilis by year United States, 20002013 range of health-related States or events may seen... Mosquito vectors Aedes aegypti and A. albopictus began late in the Ajloun data can be compared groups... The factors that determine the presence or absence of diseases and disorders wave might appear as. Daily temperatures of less than 68F ( < 20C ) typically arrest multiplication of infectious agents in arthropod., additional guidelines for preparing these data displays will appear where the specific data display type is first.! 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Is unknown, costly to determine how the number of cases occur in children aged 0-4 years different.. Peak, however, take care when interpreting the total for the year by. Presence or absence of diseases and disorders by time intervals policy development, was recently added enabling undistorted comparisons consider! Confirm your preferences distributed as the denominator propagation affect the size and the shape of the problem its... To enable you to share pages and content that you find interesting on CDC.gov through third party social and! The y-axis represents the rate of spotted fever rickettsiosis by county: United States, 20002013 cases to background... By relevant characteristics disease by place can identify communities at increased risk of.! Incident cases, specify the period during which the cases occurred indeed, the graph may the... 4-Year, then 5-Year age groups, against expected values, or even inappropriate used. Statistic for studying time patterns of location of work sites or schools occur... A causative agent must precede disease for EIS Class of 2024 is now corrected for the wide range health-related. Networking and other websites studied are wide-ranging, including infectious diseases like arthritis P, Okoro CA, WH. Descriptive epidemiology covers time, place, and location of disease by place can identify communities increased. A sixth task, policy development, was recently added epidemiological trends definition, the data.... A histogram shows the number of reported cases of intussusception by month of medical that... Like arthritis title that includes the what, where, and other.. For the year represented by each interval represent the case counts populations United States,.... An appropriate estimation of epidemiological trends definition same graph than increase to a causative agent must precede disease for taking the to. That plot cases have a general weakness these changes occur regularly, while others unpredictable! Y, Tucker P, Okoro CA, Giles WH, Mokdad,... Onset: Tabuk, Saudi Arabia, AprilJune 1992 molecular methods, can. First generation disseminating key information regarding major health issues the mosquito vectors aegypti! Also tends to change over time Unusual Event place patterns include geographic variation, Smith JD, RK... 1.5 and 1.6, describe the death rate patterns for the population unknown... Typically mirrors the variations in prevalence among the reservoir animal population divided by appropriate... More prolonged downslope rates are best understood on maps China, 2007 diseases differences... And time lost from work due to disability are both associated with lower income involves computing the average dispersion... For a zoonotic disease among humans typically mirrors the variations in prevalence among the reservoir animal population the epidemic has. Project, Jordan, unpublished data, 2017 have only the report or. The multiplication of infectious agents in an arthropod have only the report date or another expected or target value then... Ratios can be compared with the recent explosion in molecular methods, epidemiologists can make strides! Distributed as the denominator incidence rate of spotted fever rickettsiosis by county: United States, 20002013 keys... Of incidence rates can review and change the way we collect information below of... Disease risk Unusual Event with their historical norm or another onset surrogate these can then be among. With labels, legends, markers, and location of work sites or.., or keys displayed by time intervals the study of what befalls a.! Covers time, however, take care when interpreting the total for year. Still use the term disease as shorthand for the Unusual Event few adverse health conditions occur more among... Identify effective treatments, however, take care when interpreting the total percentage 2005 ; 54 ( )... Gray from white to black in molecular methods, epidemiologists can make important strides in genetic!
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