Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. The frequency of many adverse health conditions increases with decreasing socioeconomic status. Differences in racial, ethnic, or other group variables may reflect differences in susceptibility or exposure, or differences in other factors that influence the risk of disease, such as socioeconomic status and access to health care. When interpreting spot maps, keep in mind the population distribution with particular attention to unpopulated (e.g., parks, vacant lots, or abandoned warehouses) or densely populated areas. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures. 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. 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. : Adapted from Ajloun Non-Communicable Disease Project, Jordan, unpublished data, 2017. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems ( 1 ). If known, sites that are relevant, such as probable locations of exposure (water pumps in Figure 1.1), are usually noted on the map. Data Source: Heymann DL, Rodier G. Global Surveillance, National Surveillance, and SARS. Descriptive epidemiology covers time, place, and person. Return to text. Some diseases such as influenza and West Nile infection are known to have characteristic seasonal distributions. Table 1.5 Deaths and Death Rates for an Unusual Event, by Sex and Socioeconomic Status, Table 1.6 Deaths and Death Rates for an Unusual Event, by Age and Socioeconomic Status. Rates are normally displayed on area maps (e.g., patch or choropleth). If using color, use increasing intensities of the same hue. 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. To show the time course of a disease outbreak or epidemic, epidemiologists use a graph called an epidemic curve. Some of the common types of time-related graphs are further described below. 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. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. The dot chart is the most versatile and the easier to understand, particularly as categories increase in number. For some conditions, displaying data by day of the week or time of day may be informative. Rates, Ratios, and Alternative Denominators. Reported incidence rate of spotted fever rickettsiosis by county: United States, 20002013. 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. Current Trends 375 Human Arboviral Activity United States, Caribbean, Central America International Notes 376 Quarantine Measures Epidemiologic Notes and Reports Follow-up on Vibrio cholerae infection Louisiana New York: Oxford University Press; 2001. p. 61. Liao Y, Tucker P, Okoro CA, Giles WH, Mokdad AH, Harris VB, et. Differences by hour are easily seen. Second, age is a strong independent determinant for many causes of morbidity and mortality. A moving average line underlying the data markers. definition: "Epidemiology is that field of medical science which is concerned with the relationship of various factors and conditions which determine the frequencies and . Consider the data in Tables 1.3 and 1.4. Rather than increase to a peak, however, this type of epidemic curve has a plateau. A lock (LockA locked padlock) Always check whether data sources are providing incident (new events among the population) or prevalent (an existing event at a specific point in time) cases. (More techniques for graphic presentation are discussed in Lesson 4.). If the denominator of the population unit is known, spots of different size or shading (Box 6.10) can represent rates or ratios. Therefore, the clinician and the epidemiologist have different responsibilities when faced with a person with illness. Much of the data that epidemiologists collect comes from self-reportfrom answers provided by people participating in a study. Tabulate the frequency of clinical signs, symptoms, and laboratory findings among children with chickenpox in Cincinnati, Ohio. The x-axis represents a period of interest. Thank you for taking the time to confirm your preferences. 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. Table 1.4 Reported Cases of SARS through November 3, 2004 United States, by High-Risk Area Visited, * 158 reported case-patients visited 232 areas. Presented at the Eastern Regional Epidemic Intelligence Service Conference, March 23, 2000, Boston, Massachusetts. Dictionary of epidemiology. A few adverse health conditions occur more frequently among persons of higher socioeconomic status. These cookies may also be used for advertising purposes by these third parties. Return to text. Use the smallest possible administrative area that the numerator and denominator will allow. Each person providing such an answer may interpret trouble hearing differently. Disease or unhealthy conditions also can be measured on a continuous scale rather than counted directly (e.g., body mass index [BMI], blood lead level, blood hemoglobin, blood sugar, or blood pressure). 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. These might include detailed administrative boundaries or a longitude-latitude grid. Contrast this with chronic diseases that can have exposures lasting for decades before development of overt disease. In Figure 1.7, farm tractor fatalities are displayed by days of the week. Fourth, the epidemiologist can identify areas or groups within the population that have high rates of disease. Contact between severe acute respiratory syndrome (SARS) cases among a group of relatives and health care workers: Beijing, China, 2003. Stacking different strata atop one another (as in Figure 6.7, which is not recommended) defeats attempts to compare the time patterns by group. These are widely dispersed, indicating that they did not acquire their infection from their local environs. Saving Lives, Protecting People, Principles of Epidemiology in Public Health Practice, Third Edition, http://cdc.gov/od/oc/media/presskits/sars/cases.htm, http://cancer.org/docroot/PRO/content/PRO_1_1_ Cancer_ Statistics_2005_Presentation.asp, http://www.cancer.org/Research/CancerFactsFigures/cancer-facts-figures-2005/, Deputy Director for Public Health Science and Surveillance, Center for Surveillance, Epidemiology, and Laboratory Services, Division of Scientific Education and Professional Development, U.S. Department of Health & Human Services. When the pattern of the spots forms a compact, linear pattern, suspect a strong association between the two variables. Lung cancer deaths in men is higher than for women but has been decreasing slightly since the early 1990s. You should match only one term per activity. Epidemiological trends were graphically shown and the statistical significance of differences was evaluated using a linear regression model and analysis of variance. The majority of cases occur in children aged 0-4 years. Age represents three different categories of determinants of disease risk (Box 6.11). Thus, incidence divided by an appropriate estimation of the population yields several versions of incidence rates. You should also use a logarithmic scale for comparing two or more population groups. These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. Description: Histogram shows each case represented by a square stacked into columns. Heyman DL, Rodier G. Global surveillance, national surveillance, and SARS. This information in turn provides important clues to the causes of the disease, and these clues can be turned into testable hypotheses. 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. The definition of a disorder also tends to change over time, however, making estimates more difficult. In surveillance systems, you might have only the report date or another onset surrogate. Saving Lives, Protecting People, Principles of Epidemiology in Public Health Practice, Third Edition, Deputy Director for Public Health Science and Surveillance, Center for Surveillance, Epidemiology, and Laboratory Services, Division of Scientific Education and Professional Development, U.S. Department of Health & Human Services, ____ 1. Rapid Assessment of Injuries Among Survivors of the Terrorist Attack on the World Trade Center New York City, September 2001. These three points should bracket the exposure period. Goodman RA, Smith JD, Sikes RK, Rogers DL, Mickey JL. aRotaShield, Wyeth-Lederle, Collegeville, Pennsylvania Using three or more significant figures interferes with comparison and comprehension. Secular (long-term) trends. Organize data by magnitude (sort) across rows and down columns. Recognizing disease patterns by personal attributes (e.g., age, sex, education, income, or immunization status) constitutes the fifth element in descriptive epidemiology. A Salmonella Enteriditis outbreak in Chicago. cDefined as current use of asthma medicine or one or more of the following symptoms during the previous 12 months: wheezing or whistling in the chest, awakening with a feeling of chest tightness, or attack of asthma. Socioeconomic status. People who work in this field are referred to as epidemiologists. 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