This aggregation of cases seems to be unusual, but frequently the public (and sometimes the health agency) does not know the denominator. When designing a case-control study, you must consider a variety of other issues about controls, including how many to use. MacDonald KL, Spengler RF, Hatheway CL, Hargrett NT, Cohen ML. As a field investigator, you must have the appropriate scientific knowledge, supplies, and equipment to carry out the investigation before departing for the field. (34) The most cases occurred in Washburn (n=21) and Chippewa (n=17) Counties. Descriptive epidemiology describes the where and whom of the disease, allowing you to begin intervention and prevention measures. Generally, an exposure that has the following three characteristics or criteria is considered a strong suspect: Relative and attributable risk. In contrast to outbreak and epidemic, a cluster is an aggregation of cases in a given area over a particular period without regard to whether the number of cases is more than expected. Positive cerebrospinal fluid (CSF) antigen detection or positive culture. The answer is public health surveillance. Figure 6.7 Desk Locations of Persons with Nasal Swabs Positive for Bacillus anthracis, Hart Building Washington, DC, 2001. In addition, the p-value is exceedingly small, less than 0.001, and far less than the commonly used cutoff of 0.05. Diagnoses may be uncertain, particularly early in an investigation. Consider the following data from an outbreak of gastroenteritis among college football players. When is the likely dates of exposure, based on the minimum incubation period before the first case? First, review the clinical findings and laboratory results. Recover. Public health surveillance is "the ongoing, systematic collection, analysis, and interpretation of health-related data essential to planning, implementation, and evaluation of public health practice." Field Epidemiology These materials provide an overview of public health surveillance systems and methods. Table 6.2 Epidemiologic Steps of an Outbreak Investigation. Alternatively, they may conduct active surveillance by telephoning or visiting the facilities to collect information on any additional cases. Source Ramsey AH, Belongia EA, Gale CM, Davis JP. Jernigan DB, Raghunathan PL, Bell BP, Brechner R, Bresnitz EA, Butler JC, et al. An intermittent common-source epidemic (in which exposure to the causative agent is sporadic over time) usually produces an irregularly jagged epidemic curve reflecting the intermittence and duration of exposure and the number of persons exposed. Sample size formulas are available to help you make this decision. Even if the cases turn out to be the same disease, the number of cases may not exceed what the health department normally sees in a comparable time period. Why are some groups with particular age, sex, or other person characteristics at greater risk than other groups with different person characteristics? Occasionally, you may be asked to draw an epidemic curve when you dont know either the disease or its incubation time. Eosinophilia-myalgia syndrome New Mexico. Whether an apparent problem should be investigated further is not strictly tied to verifying the existence of an epidemic (more cases than expected). For example, acquired immunodeficiency syndrome (AIDS) and severe acute respiratory syndrome (SARS) both began with relatively specific case definitions. Review the six case report forms in Figure 6.1. When an outbreak occurs, whether it is routine or unusual, consider what questions remain unanswered about that particular disease and what kind of study you might do in this setting to answer some of those questions. Solna, Sweden: Smittskyddsinstitutet [updated 2004 Sep 27; cited 2006 Sep 22]. They help us to know which pages are the most and least popular and see how visitors move around the site. Fortunately, potential controls are usually plentiful. A communications plan must be established. This audit has two main purposes; firstly, it ensures that you have the quality management system is in place and is ready to audit. Outliers cases that dont fit into the body of the curve may provide important clues. Surveillance identifies new cases and detects importation of wild poliovirus The four steps of surveillance are: 1. But every step you take will make you a little bit safer than average. Discovery and. Making a change shouldn't be a one time action. The attack rate is low among those not exposed, so the difference or ratio between attack rates is high. The plan should include how often and when to have conference calls with involved agencies, who will be the designated spokesperson, who will prepare health alerts and press releases, and the like. Renault (Claude Rains) to his policemen after Rick Blaine (Humphrey Bogart) had just shot a Nazi officer, Casablanca, 1942. This sounds pretty obvious but youd be surprised. The case definition may be restricted by time (for example, to persons with onset of illness within the past 2 months), by place (for example, to residents of the nine-county area or to employees of a particular plant) and by person (for example, to persons with no previous history of a positive tuberculin skin test, or to premenopausal women). The two most commonly described host characteristics are age and sex because they are easily collected and because they are often related to exposure and to the risk of disease. You could calculate a p-value that is not less than 0.05 and consequently fail to reject the null hypothesis, which may turn out to be true. By asking about drug use in a second case-control study, the investigators implicated marijuana as the likely vehicle. Because the Fisher Exact Test is tedious to calculate, let Epi Info or another computer program perform the calculations for you. Third, summarize the clinical features using frequency distributions. If patient information is disclosed to unauthorized persons without the patients permission, the patient may be stigmatized or experience rejection from family and friends, lose a job, or be evicted from housing. : Yes; Hospital Alerted: Yes; Lab Results: WB IgM+, WB IgG+;Comments: Erythema migrans, arthritis, fatigue, sweats, fever; Physician Reporting: Dr. Farr; Phone: 555-1313; Date of Report: 11/24/06. Outliers also can provide important clues. Some interventions are aimed at blocking the mode of transmission. Peterson LR, Marshall SL, Barton-Dickson C, Hajjeh RA, Lindsley MD, Warnock DW, et al. Patients from the same physician practice or hospital who do not have the disease in question. The data showing the relationship between an exposure and disease are often displayed in a two-by-two table. Thus, a line listing contains key information on every case and can be scanned and updated as necessary. This is a common mistake. In addition, no illness was reported among students who did not go on the field trip, and no cases of E. coli O157 were reported in the community that week. Source: Treadwell TA, Koo D, Kuker K, Khan AS. Research for a new drug begins in the laboratory. Supply chains now account for nearly 25 percent of pharmaceutical costs and more than 40 percent of medical-device costs. Finally, particularly in areas with sudden changes in population size such as resort areas, college towns, and migrant farming areas, changes in the numerator (number of reported cases) may simply reflect changes in the denominator (size of the population). The population attributable risk percent for beef was 76.7% (see Table 6.8), much higher than that for any other food. How is it usually transmitted? You must arrange travel, lodging, and local transportation. Step 3: Work on the plan as a team. Is the attack rate low among persons not exposed to that item? Reporting may rise because of changes in local reporting procedures, changes in the case definition, increased interest because of local or national awareness, or improvements in diagnostic procedures. Most of the case-patients were exposed to the item, so that the exposure could explain or account for most, if not all, of the cases. Most, perhaps all, used cell phones. New cases are added to a line listing as they are identified. Depression. Typically, hypotheses in a field investigation are evaluated using a combination of environmental evidence, laboratory science, and epidemiology. Interruption of direct transmission may be accomplished by isolation of someone with infection, or counseling persons to avoid the specific type of contact associated with transmission. Presented at Northeast Regional Epidemic Intelligence Service Conference, March 14, 2002, New York City. A questionnaire could be distributed to determine the true occurrence of clinical symptoms, or laboratory specimens could be collected to determine the number of asymptomatic cases. [Note that persons infected with E. coli O157 typically experience severe abdominal cramps, bloody diarrhea, and low grade fever after a 1 to 8day incubation period (usually 24 days). : Yes; Lab Results: WB IgG+; Comments: Arthritis, arthralgias, headache, fatigue, sweats, chills; Physician Reporting: Dr. Howard; Phone: 555-1950; Date of Report: 11/24/06. Using the dates of onset listed below, draw an epidemic curve. This part includes the STEPS Instrument as well as the question-by-question guide, the show cards, and . Collectively, these systems provide raw data for descriptive epidemiology that is vital for a number of important public health functions, including: Monitoring and reporting on the health status and health related behaviors in . (24) Here you can see the different categories that PAHO uses for this diagnosis. Early (and continuing) analysis of descriptive data helps you to become familiar with those data, enabling you to identify and correct errors and missing values. J Infect Dis 1992;165: 7369. If criminal or bioterrorist intent is suspected, law enforcement agencies and the Federal Bureau of Investigation (FBI) may be in charge, or at least involved. Potentially correlated events can be noted on the graph. A spot map may even plot sites of recreational or other outdoor exposures. Step 10: Maintain Surveillance The characterization often provides clues about etiology, source, and modes of transmission that can be turned into testable hypotheses (see Step 7). From this characterization you can identify or infer the population at risk for the disease. In theory, a propagated epidemic one spread from person-to-person with increasing numbers of cases in each generation should have a series of progressively taller peaks one incubation period apart, but in reality few produce this classic pattern. For example, while investigating an outbreak of diarrhea on a cruise ship, investigators usually try to identify the causative organism from stool samples from a few afflicted persons. Environmental studies are equally important in some settings. Frequently, one person with an illness knows or hears of others with the same illness. 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. The population attributable risk percent describes the proportion of illness in the entire study population that could be attributable to a given exposure, assuming that those who became ill in the unexposed group and a similar proportion in the exposed group must be attributable to something else. Snow; Phone: 555-1200; Date of Report: 11/24/06. The average incubation period for coccidioidomycosis is 12 days, with a minimum incubation period of 7 days. The World Health Organization (WHO) defines public health surveillance as the "continuous, systematic collection, analysis and interpretation of health-related data needed for the planning, implementation, and evaluation of public health practice. This graph, called an epidemic curve, or epi curve for short, provides a simple visual display of the outbreaks magnitude and time trend. Figure 6.2d shows the same data one more time, but with stacks of squares that each represent one case. This is usually health care providers who provide clinical care, such as doctors, nurses, clinical officers, etc. Some cities have placed cameras on stop lights as a way to help prevent people from speeding or from going through a red light. Figure 6.4 Number of Cases of Acute Hemorrhagic Conjunctivitis, By Month and Week of Report Puerto Rico, August 7October 30, 2003. For a case-control study, the measure of association of choice is the odds ratio. quadrant, offices of Senators A & B and the hallway outside. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. Subtract the time of onset of the median case from the time of exposure to estimate the median incubation period. The hypothesis that the locally produced ground beef was the vehicle could easily be tested by asking case-patients and controls (persons without thyrotoxicosis or other thyroid disease) whether they ate ground beef from the same source. The following two-by-two table shows the data for beef and gastroenteritis. Consider convening a meeting of the case-patients to look for common links or visiting their homes to look at the products on their shelves. A case classified as probable usually has typical clinical features of the disease without laboratory confirmation. The health departments first responsibility is to protect the publics health, so if appropriate control measures are known and available, they should be initiated even before an epidemiologic investigation is launched. The Surveillance, Epidemiology, and End Results (SEER) Program provides information on cancer statistics in an effort to reduce the cancer burden among the U.S. population. The odds ratio for Grocery Store A is calculated as: An odds ratio of 11 is quite large, indicating that shopping at Grocery Store A was strongly associated with developing legionellosis. Description: Name: Clifton, R; Age: 46; Phone: 555-2110; Address: 361 Chander St., Springdale, VA; County: Columbia; Sex: Male; Race: White; Disease: Lyme Disease; Date of Onset: 8/1/2006; Lab Confirmed? In addition, investigators must consider logistical issues, such as how to contact potential controls, gain their cooperation, ensure that they are free of disease, and obtain appropriate exposure data from them. The investigators asked case-patients and controls how much time they spent in the store and where they went in the store. This information forms the basis for predicting whether more or fewer cases will occur in the near future. Unfortunately, analytic studies sometimes are unrevealing. A systematic difference between cases and controls that results in a mistaken estimate of the association between exposure and disease is called a bias. The lesson learned is that when the epidemiology does not fit the usual or natural patterns of transmission, investigators should think about intentional modes of transmission. Lukacs SL, Hsu V, Harper S, Handzel T, Hayslett J, Khabbaz R, et al. The date of onset of the first case was during the week of October 28. To test an association for statistical significance, assume first that the exposure is not related to disease, i.e., the relative risk (RR) equals 1.0. 67(36 ,1 ,19(67,*$7,1* $1 287%5($. Privacy and Surveillance The ACLU works in courts, legislatures, and communities to defend and preserve the individual rights and liberties that the Constitution and the laws of the United States guarantee everyone in this country. These clinical frequency distributions are considered so important in establishing the credibility of the diagnosis that they are frequently presented in the first table of an investigations report or manuscript. Saving Lives, Protecting People, Principles of Epidemiology in Public Health Practice, Third Edition, Section 2: Purpose and Characteristics of Public Health Surveillance, Section 3: Identifying Health Problems for Surveillance, Section 4: Identifying or Collecting Data for Surveillance, Section 5: Analyzing and Interpreting Data, Section 6: Disseminating Data and Interpretations, Section 7: Evaluating and Improving Surveillance, Summary, References, Further Reading, and Websites, Appendix D. Major Health Data Systems in the United States, Appendix E. Limitations of Notifiable Disease Surveillance and Recommendations for Improvement, 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, List the essential activities of surveillance, List the desirable characteristics of well-conducted surveillance activities, Describe sources of data and data systems commonly used for public health surveillance, Describe the principal methods of analyzing and presenting surveillance data, Describe selected examples of surveillance in the United States, Given a scenario and a specific health problem, design a plan for conducting surveillance of the problem.
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