Historical Evolution of Epidemiology (1976) PDF

Historical Evolution of Epidemiology Because Snow believed that water was a source of infection for cholera, he marked the location of water pumps on his spot map,...

Historical Evolution of Epidemiology Because Snow believed that water was a source of infection for cholera, he marked the location of water pumps on his spot map, then looked for a relationship between the distribution of households with cases of cholera and the location of pumps. He noticed that more case households clustered around Pump A, the Broad Street pump, Figure: Spot map of deaths from cholera in Golden Square area, than around Pump B or C. London, 1854 1  Scenario: Unexplained Pneumonia American Legion Health care provider at a veterans’ hospital Convention, in Philadelphia calls CDC to report cases Philadelphia, of severe respiratory illness among attendees Pennsylvania of the American Legion Convention August 2 August 2 July 21–24 July 26–Aug 1 (Morning) (Evening) 18 deaths 71 additional reported among cases reported conventioneers 2  Members of the American Legion gathered for the annual American Legion Convention held July 21 through 24, 1976, in Philadelphia. Soon after the convention began, a substantial number of attendees were admitted to hospital emergency departments or were examined in doctors’ offices with acute onset of fever, chills, headache, malaise, dry cough, and muscle pain. More troublesome is that during July 26 to August 1, a total of 18 conventioneers died, reportedly from pneumonia On the morning of August 2, a nurse at a veterans’ hospital in Philadelphia called CDC to report cases of severe respiratory illness among convention attendees. Subsequent conversations that day with public health officials uncovered an additional 71 cases among persons who had attended the convention. The goal was to find out why these conventioneers were becoming ill and, in some cases, dying 3 Legionnaires’ Disease, by Age Group Hotel A Residents Time: July 21–24, 1976 Frequency Unit size Age (yrs) Sick Total Percentage 39 3 44 6.8 40–49 9 160 5.6 50–59 27 320 8.4 60–69 12 108 11.1 70 11 54 20.4 Unknown 0 2 0 4  These cases of unexplained pneumonia were investigated and subsequently given the name Legionnaires’ disease because of the association with attendance at the American Legion Convention during July 1976. The chart depicts how CDC investigators focused on a particular hotel as the possible source of the outbreak because that was a common factor among all of the ill men. The investigators wanted to find out if any trends existed by age group among hotel guests who became ill. Here you can see the three elements that constituted the epidemiologic rates. We can calculate the rate at which each age group became ill after staying at or attending a meeting at Hotel A during the convention by using a basic formula. 5  Knowledge Check On Day 1 of a technology conference in San Diego, 15 presenters who were setting up for their sessions in Annex X became ill with flu-like symptoms. During the course of the conference, 20 participants who attended sessions in Annex X also became ill with the same symptoms. To begin calculating the rate of this outbreak, investigators should first determine A. the size of the conference population. B. the number of cases of illness. C. the number of days the conference was held. D. the location of the conference. 6  Topic 5 Epidemiology Approach and Methods 7  Epidemiology Study Types Experimental Epidemiology study Descriptive types Observational Analytic 8  In an experimental study, the investigators can control certain factors within the study from the beginning. An example of this type is a vaccine efficacy trial that might be conducted by the National Institutes of Health. In such a trial, the investigators randomly control who receives the test vaccine and who does not among a limited group of participants; they then observe the outcome to determine if it should to be used more widely In an observational study, the epidemiologist does not control the circumstances. These studies can be further subdivided into descriptive and analytic. Descriptive epidemiology is the more basic of these categories and is fundamental to what epidemiologists do. In a descriptive study, the epidemiologist collects information that characterizes and summarizes the health event or problem. 9  In the analytic study, the epidemiologist relies on comparisons between different groups to determine the role of different causative conditions or risk factors. 10 Descriptive and Analytic Epidemiology Descriptive Analytic epidemiology epidemiology When was the How was the population affected? population affected? Where was the Why was the population affected? population affected? Who was affected? 11 Fatalities Associated with Farm Tractors In 1982, the number of farm tractor-associated deaths was described in terms of time, place, and person by using records from an existing surveillance system 12  In 1982, an epidemiologist in the Georgia Department of Public Health became interested in the number of deaths associated with farm tractors. He determined he could examine this problem by using readily available data — death certificate records that were included in an existing surveillance system. He obtained the death certificate records for all deaths that had occurred in Georgia during 1971 through 1981 that were associated with farm tractor incidents. After collecting the data, he used the information to describe the problem in terms of time, place, and person and then generated a hypothesis for further study. 13 Fatalities Associated with Farm Tractors 14  This graph describes the when for 166 of the farm tractor-associated deaths. We can examine the data by looking at the time of day when the deaths occurred. What inferences can we make from this graph? Peaks in deaths occurred just before lunch and during late afternoon. We can infer that deaths occur when farmers are probably most fatigued right before lunch, which might lead to the increase in deaths in late morning. More deaths occur in late afternoon when children are home from school. Conversely, fewer deaths occur while the farmers are probably eating their lunch. 15 Fatalities Associated with Farm Tractors An increase in the number of deaths occurred among older persons, which again, is part of the descriptive analysis. 16 Fatalities Associated with Farm Tractors Most of the deaths occurred in the northern areas of Georgia, which has a more mountainous terrain. Fewer deaths occurred in south-central Georgia, which is characterized by much flatter farmlands. 17  Knowledge Check Choose the correct answer from the following choices: A. Qualitative B. Experimental C. Observational C. Observational An epidemiologist is doing a study on the sleep patterns of college students but does not provide any intervention. What type of study is this? 18  Knowledge Check Match each term to the correct example below. A. Descriptive B. Analytic B. Analytic 1. A study of heart disease comparing a group who eats healthy foods and exercises regularly with one who does not in an effort to test association A. Descriptive 2. A study to describe the eating habits of adolescents aged 13–18 years in Community X 19  Topic 6 Epidemiology Data Sources and Study Design 20  Data Sources and Collection Methods Source Method Example Individual persons Questionnaire Foodborne illness outbreak Survey Health data on U.S. residents Environment Samples from the Collection of water — check environment (river for chemical water, soil) Sensors for environmental changes Health care Notifications to health Report cases of meningitis to providers department if cases of health department certain diseases are observed Nonhealth–related Sales records Cigarette sales sources (financial, Court records Intoxicated driver arrests legal) 21 Conducting Studies Studies are conducted in an attempt to discover associations between an exposure or risk factor and a health outcome 22 Cross-Sectional Study Patient studied based on being part of a group. Ex. Newyorkers women Tall people 23  Cross-Sectional Study Frequency of disease and risk factors identified - how many have lung cancer - how many smoke Patient not followed for month/years The main outcome of this study is prevalence -50% of New Yorker smoke -25% of New Yorkers have lung May have more than one group -50% of men have lung cancer and 25% of women have lung cancer Group not followed over time 24  Cross-Sectional Study Example 1: New Yorkers were surveyed to determine whether they smoke and whether they have a morning coffee the study found a smoking prevalence of 50% among responders 25 percent reported morning coffee what type of study? what can be determined? 25  Cross-Sectional Study Example 2: using a national u.s. database rates of lung cancer were determined among New Yorkers Texans and Californians lung cancer prevalence was 25% in New York 30% in Texas and 20% in California the researchers concluded that living in Texas is associated with higher rates of cancer so some key points here because there are different groups this might confuse you and make you think that this is some type of case control or cohort study but it's not note that there is a lack of a time frame 26  Cross-Sectional Study Example 3: researchers discover a gene that they believe leads to development of diabetes a sample of 1000 patients is randomly selected all patients are screened for the gene presence or absence of diabetes is determined from a patient questionnaire it is determined that the gene is strongly associated with diabetes key points here note the lack of a time frame they're not following patients for years so this makes it very likely it's a cross-sectional study note that the patients are not selected by disease or exposure which is the way they're selected for cohort and case-control studies 27  Cohort Study compare a group with exposure to a group without and it's very important that you remember that this is the way patients are identified they are identified by exposure so for example if we wanted to whether smoking causes lung cancer we would identify patients based on whether they smoke or not. by monitoring them over time whether exposure changes the likelihood of disease 28  Cohort Study most cohort studies are what's called prospective it means they identify patients with/without the exposure and monitor them going forward in time sometimes they're done retrospectively so you can look back in time and see whether or not they had disease 29  Cohort Study the main outcome measure of a cohort study is a relative risk which is defined by the risk ratio represents how much exposure increases the risk of disease an example of the results you might get from a cohort study you might find that 50% of smokers get lung cancer within five years 10% of non-smokers get lung cancer within 5 years this would give you a risk ratio of 50 divided by 10 and this means that smokers are 5 times more likely to get lung cancer than non-smokers 30  Cohort Study Example: a group of 100 New Yorkers who smoke were identified based on a screening questionnaire at a local hospital these patients were compared to another group that reported no smoking both groups received follow-up surveys asking about development of lung cancer annually for the next three years the prevalence of lung cancer was 25 percent among smokers and 5 percent among non-smokers. what type of study ? it's a prospective cohort study 31 Case-Control Study Subjects identified as having a disease or condition are compared with subjects without the same disease or condition 32  Case-Control Study the opposite of a cohort study instead of identifying exposure and looking for disease in this case we're looking for disease first and then exposure an example of a case control study might be people with lung cancer and your cases have to have a mixture of exposed and unexposed you can't just identify smokers with lung cancer you've got to have some smokers and some non-smokers and then you've got to go and find a control group and the control group also has to contain a mixture of smokers and non- smokers exposed or unexposed patients once you've 33 QUESTIONS? 34