Recognizing disease patterns by personal attributes (e.g., age, sex, education, income, or immunization status) constitutes the fifth element in descriptive epidemiology. Reported incidence rate of spotted fever rickettsiosis by county: United States, 20002013. In fact, epidemiology is often described as the basic science of public health, and for good reason. This count of incident cases over time in a population is called incidence. In this chapter, additional guidelines for preparing these data displays will appear where the specific data display type is first applied. . Each spot in the plotting area represents the joint magnitude of the two variables. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests. Person attributes include age, sex, ethnicity/race, and socioeconomic status. Many definitions have been proposed, but the following definition captures the underlying principles and public health spirit of epidemiology: 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). Age-specific mortality rates per 100,000 population/year: United States, 1910, 1950, and 1998. Compiling and analyzing data by time, place, and person is desirable for several reasons. Generation periods between waves of an outbreak are usually longer than with simple person-to-person transmission because two sequential incubation periods, extrinsic in the vector and intrinsic in the human, are involved. Other relevant events supplementing a chronologic framework of a health problem include underlying environmental conditions, changes in health policy, and application of control and prevention measures. Align columns of numbers on the decimal point (or ones column). To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the Why and How of such events. 1a - Epidemiology 1b - Statistical Methods 1c - Health Care Evaluation and Health Needs Assessment 1d - Qualitative Methods Disease Causation and Diagnostic 2a - Epidemiological Paradigms 2b - Epidemiology of Diseases of Public Health Significance 2c - Diagnosis and Screening 2d - Genetics 2e - Health and Social Behaviour 2f - Environment epidemiologic transition theory was the suggestion that the causes of death that had dominated human history would be replaced by the chronic degenera . Description: Histogram shows each case represented by a square stacked into columns. Public Health Rep 1985;100:32933. A title that includes the what, where, and when that identifies the data it introduces. As noted above, time is plotted along the x-axis. There is a clear linear trend; countries with the . Return to text. Make sure overlapping plotting symbols are distinguishable. Dot chart (A) and bar chart (B) comparison of mean body mass index among adults, by age group and sex: Ajloun and Jerash Governorates, Jordan, 2012. Key terms in this definition reflect some of the important principles of epidemiology. Through this process of organization, inspection, and interpretation of data, descriptive epidemiology serves multiple purposes (Box 6.1). The most commonly studied rate is the attack rate . This demonstrates how review of secular trends can bring attention to key events, improvements in control, changes in policy, sociologic phenomena, or other factors that have modified the epidemiology of a disease. Significant spacetime clustering (assessed by the Knox test) of dengue cases in the city of Cairns, Australia, during JanuaryAugust 2003. The line indicates the rapid decrease in Aedes-infested houses (house index). Nonetheless, many epidemiologists still use the term disease as shorthand for the wide range of health-related states and events that are studied. 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. Source: Dowell SF. Aspect ratios (data space width to height) of approximately 2:1 work well. Return to text. 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. (for example, trends, outbreaks, etc. : Adapted from Ajloun Non-Communicable Disease Project, Jordan, unpublished data, 2017. The shape and other features of an epidemic curve can suggest hypotheses about the time and source of exposure, the mode of transmission, and the causative agent. Compute and plot rates for the smallest area possible. Consequently, they also accelerate and amplify epidemic development. Figure 1.6 shows the seasonal patterns of rubella, influenza, and rotavirus. aRotaShield, Wyeth-Lederle, Collegeville, Pennsylvania For other conditions, such as foodborne outbreaks, the relevant time scale is likely to be days or hours. Two important qualifications apply to person data assessments. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. trends in age-related diseases. Figure 1.15 Infant Mortality Rates for 2002, by Race and Ethnicity of Mother. In other words, the word epidemiology has its roots in the study of what befalls a population. To assess the epidemiological trends and hotspots of OID in mainland China, the data of OID including the number of cases and deaths, the incidence and mortality were stratified by date (month and year), age and region. 2003;10:1735. This puts each stratum on a flat baseline, enabling undistorted comparisons. As an alternative to plotting onset by calendar time, plotting the time between suspected exposures and onset can help you understand the epidemiologic situation. Age represents three different categories of determinants of disease risk (Box 6.11). A more precise approach involves computing the average and dispersion of the individual measurements. Available from: http://cancer.org/docroot/PRO/content/PRO_1_1_ Cancer_ Statistics_2005_Presentation.asp. On an arithmetic scale, represent equal numerical units with equal distances on an axis. A moving average line underlying the data markers. Descriptive epidemiology uses observational studies of the distribution of disease in terms of person, place, and time. Dot plots, box plots, and bar charts are easier to understand and read if aligned horizontally (with the numeric axis horizontal). For diseases that occur seasonally, health officials can anticipate their occurrence and implement control and prevention measures, such as an influenza vaccination campaign or mosquito spraying. Fourth, the epidemiologist can identify areas or groups within the population that have high rates of disease. Cookies used to make website functionality more relevant to you. Cookies used to make website functionality more relevant to you. Thank you for taking the time to confirm your preferences. The following sections describe certain kinds of epidemic situations that can be diagnosed by plotting cases on epidemic curves. Decrease the time interval size as case numbers increase. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website. For example, the consistent time interval between rotavirus vaccination and onset of intussusception (Table 6.1) helped build the hypothesis that the vaccine precipitated the disease (1). Do not stack columns for different groups atop one another in the same graph. Or they may in part reflect an interdependent relationship that is impossible to untangle: Does low socioeconomic status contribute to disability, or does disability contribute to lower socioeconomic status, or both? Usually epidemiologists begin the analysis of person data by looking at each variable separately. For example, Figure 1.14 shows the differences in lung cancer rates over time among men and women. not-set Epidemiological trends were difficult to assess. Use graphic designs that reveal the data from the broad overview to the fine detail. To compare two lines, plot their difference directly. Describing the occurrence of disease by place provides insight into the geographic extent of the problem and its geographic variation. Second, age is a strong independent determinant for many causes of morbidity and mortality. For these larger areas, stratifying the epidemic curves by smaller subunits can reveal the underlying periodicity. However, epidemiologists tend to use synonyms for the five W's listed above: case definition, person, place, time, and causes/risk factors/modes of transmission. Random or uniform distributions indicate that the exposure lies outside the group. They begin with a single or limited number of cases and increase with a gradually increasing upslope. If a rapidly acting intervention was taken early enough to prevent cases, discount the contribution of the last cases to this estimation. A Salmonella Enteriditis outbreak in Chicago. Voice: (800) 241-1044 The x-axis represents a period of interest. Seasonal patterns may suggest hypotheses about how the infection is transmitted, what behavioral factors increase risk, and other possible contributors to the disease or condition. 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. Rates correct counts for differences among population sizes or study periods. These graphs can include line graphs, histograms (epidemic curves), and scatter diagrams (see Box 6.4 for general guidelines in construction of epidemiologic graphs). 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. You will be subject to the destination website's privacy policy when you follow the link. The last two factors listed in the box will lead to irregular peaks during the progression of the outbreak and precipitous decreases. They assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, or other so-called potential risk factors. These three points should bracket the exposure period. In Figure 1.7, farm tractor fatalities are displayed by days of the week. People who work in this field are referred to as epidemiologists. The rapid increase, plateau, and precipitous downslope all appeared with a salmonellosis outbreak from cheese distributed to multiple restaurants and then recalled (Figure 6.5). Establishing a case definition and finding cases; . Epidemiologic Criteria. Return to text. This propagated pattern has four principal characteristics (Box 6.6). These tasks are described below. However, sometimes the population is unknown, costly to determine, or even inappropriate. 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. 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. A number of factors that also vary with age include: susceptibility, opportunity for exposure, latency or incubation period of the disease, and physiologic response (which affects, among other things, disease development). 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. This expected or target case count is now corrected for the population and can be compared with the actual observed case counts. Place numbers close together, which might require using abbreviations in column headings. To answer this question, different age groups are needed. Rash or poxvirus-like lesions, which may be: Macular, papular, vesicular, or pustular The difference is that epidemiologists tend to use synonyms for the 5 Ws: diagnosis or health event (what), person (who), place (where), time (when), and causes, risk factors, and modes of transmission (why/how). You should match only one term per activity. Summarize with average rates, average counts, or totals for all the Januarys, Februarys, and so on for each of the 12 months. Topics of study may include comparative healthcare systems, medical informatics, and survey and . These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data. 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