Epidemiology Lecture Notes PDF

A L M ash r e q U ni v e r si t y College Of Pharmacy Epidemiology DI L AN ZA KA R IA C l i n i cal P h ar ma cy S p eci a l i s t ( F IB M S )  A PUBLIC HEALTH APPROACH Public health problems are diverse and can include infectious disease, chronic...

A L M ash r e q U ni v e r si t y College Of Pharmacy Epidemiology DI L AN ZA KA R IA C l i n i cal P h ar ma cy S p eci a l i s t ( F IB M S )  A PUBLIC HEALTH APPROACH Public health problems are diverse and can include infectious disease, chronic disease, emergencies, injuries, environmental health problems, as well as other health threats. Regardless of the topic, we take the same approach to a public health problem by following four general steps Public Health Core sciences ▪ To implement the public health approach, practitioners use and apply scientific methods. These methods come from a series of core sciences that provide the foundation. ▪ These sciences include Public Health Surveillance, which we use to monitor a public health situation. ▪ Epidemiology enables us to determine where diseases originate, how or why they move through populations, and how we can prevent them. ▪ Public Health Laboratories support public health by performing tests to confirm disease diagnoses. Laboratories also support public health by conducting research and training. ▪ As we continue to move from the use of paper documents to electronic health records, Public Health Informatics continues to increase in importance. Informatics deals with the methods for collecting, compiling, and presenting health information. It enables us to use electronic data effectively when addressing a public health situation. ▪ Prevention Effectiveness is closely linked to public health policy. Prevention effectiveness studies provide important economic information for decision makers to help them choose the best option available. ▪ these five core sciences can help us protect and promote the public’s health by giving public health practitioners the answers they need. Public health is better able to respond to the situation by using contributions from each of these sciences. One science alone cannot answer the questions and provide a solution WHAT IS EPIDEMIOLOGY? The branch of medicine that deals with the study of the occurrence and distribution of health-related disease or events in specified populations. Including the study of the determinants influencing such states, and the application of this knowledge to control the health problem. Study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems. Epidemiology purposes in Public Health Practice Discover the agent, host, and environmental factor that affect health Determine the relative importance of causes of illness, disability, and death Identify those segments of the population that have the greatest risk from specific causes of ill health Evaluate the effectiveness of health programs and services in improving population health  Solving Health Problem Step 1 Step 1 - Data Surveillance; determine collection time, place, and person Step 2 Step 2 Assessment Inference Solving health problems Step 3 Step 3 Hypothesis Determine how and why testing Step 4 Step 4 Action Intervention Action First, data are collected about health problems occurring among the population through public health surveillance. The data collected include information about when the problem occurred, as well as where and who were affected (that is, time, place, and person). This is known as descriptive epidemiology. Next, the epidemiologist establishes inferences on the basis of the collected data and draws initial conclusions on the basis of those data. From there, he or she uses the information to generate hypotheses about what might be causing the health problem Then, the how and why of a condition is determined by conducting tests or studies to determine if the hypothesis is accurate. This determination of how and why is known as analytic epidemiology. Finally, the epidemiologist takes action. In public health, that action is known as an intervention. We take action to intervene to prevent the condition from spreading further or to promote healthy behaviors. The epidemiologist recommends or implements some form of action at the population level (for example, a community intervention.)  Epidemiology key Terms ……. Epidemic or outbreak: disease occurrence among a population that is in excess of what is expected in a given time and place. Cluster: group of cases in a specific time and place that might be more than expected.  Epidemiology key Terms Endemic: disease or condition present among a population at all times. Pandemic: a disease or condition that spreads across regions. Rate: number of cases occurring during a specific period; always dependent on the size of the population during that period.  Comparing Population Characteristics Rates help us compare health problems among different populations that include two or more groups who differ by a selected characteristic  Rate Formula To calculate a rate, we first need to determine the frequency of disease, which includes the number of cases of the illness or condition the size of the population at risk the period during which we are calculating the rate 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, than around Pump B or C. Figure: Spot map of deaths from cholera in Golden Square area, London, 1854  Scenario: Unexplained Pneumonia American Legion Health care provider at a veterans’ hospital in Convention, Philadelphia calls CDC to report cases Philadelphia, of severe respiratory illness among attendees of the Pennsylvania American Legion Convention August 2 August 2 July 21–24 July 26–Aug 1 (Morning) (Evening) 18 deaths reported 71 additional cases among reported conventioneers Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297:1189–97.  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  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 Fraser DW, Tsai, T, Orenstein W, et al. Legionnaires’ disease: description of an epidemic of pneumonia. New Engl J Med 1977;297:1189–97.  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.  Legionnaires’ Disease Rate Hotel A Residents Time: July 21–24, 1976 Frequency Unit Rate 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 Epidemiology Approach and Methods  Epidemiology Study Types Experimental Epidemiology study types Descriptive Observational Analytic 26  Experimental study 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. In the analytic study, the epidemiologist relies on comparisons between different groups to determine the role of different causative conditions or risk factors. Descriptive and Analytic Epidemiology Descriptive Analytic epidemiology epidemiology When was the How was the population affected? population affected? Where was the population Why was the affected? population affected? Who was affected? 29 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  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.  Fatalities Associated with Farm Tractors Goodman RA, Smith JD, Sikes RK, et al. Fatalities associated with farm tractor injuries: an epidemiologic study. Public Health Rep 1985;100:329–33.  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.  Fatalities Associated with Farm Tractors An increase in the number of deaths occurred among older persons, which again, is part of the descriptive analysis. Goodman RA, Smith JD, Sikes RK, et al. Fatalities associated with farm tractor injuries: an epidemiologic study. Public Health Rep 1985;100: 329–33.  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. Goodman RA, Smith JD, Sikes RK, et al. Fatalities associated with farm tractor injuries: an epidemiologic study. Public Health Rep 1985;100:329–33. Epidemiology Data Sources and Study Design  Data Sources and Collection Methods Source Method Example Individual persons Questionnaire Foodborne illness outbreak Survey CDC’s National Health and Nutrition Examination Survey Health data on U.S. residents Environment Samples from the Collection of water from area environment (river water, streams — check for chemical soil) pollutants Sensors for environmental Air-quality ratings changes Health care providers Notifications to health Report cases of meningitis to health department if cases of department certain diseases are observed Nonhealth–related Sales records Cigarette sales sources (financial, Court records Intoxicated driver arrests legal) 37 Conducting Studies Studies are conducted in an attempt to discover associations between an exposure or risk factor and a health outcome 38 Study Design — Cross-Sectional Study Subjects are selected because they are members of a certain population subset at a certain time 39  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 cancer May have more than one group -50% of men have lung cancer and 25% of women have lung cancer Group not followed over time  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? Study Design — Cohort Study Subjects are categorized on the basis of their exposure to one or more risk factors 42  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  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  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  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 Study Design Type — Case-Control Study Subjects identified as having a disease or condition are compared with subjects without the same disease or condition 47  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 Questions