Principles of epidemiology
Topic 1: Overview of Epidemiology
Objectives:
- Discuss historically significant epidemiological advances.
- Evaluate the three types of prevention used in public health interventions.
- Explore sources of epidemiologic information.
- Select quantitative and qualitative data collection methods appropriate for a given public health context.
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Define endemic, epidemic, and pandemic, and provide an example of each. Describe a current epidemic. Describe one example of each of the prevention types (primary, secondary, and tertiary) that could be applied to control the epidemic.
Topic 1 DQ 2 |
Discuss the role the CDC’s Morbidity and Mortality Weekly Report (MMWR) plays in conveying public health information and recommendations. Describe the type of data and information provided by the MMWR. Choose a report posted within the last 2 years from the “Publications – Weekly Report” tab. Provide a brief summary of the disease report, including the natural history and mode of transmission, and whether the report is an example of descriptive epidemiology or analytical epidemiology.
Topic 2: Disease Surveillance and Measurement
Objectives:
- Evaluate the effectiveness of disease surveillance in public health.
- Apply measurement tools to assess the impact of disease, its burden, and associated risk factors.
- Discuss the importance of validity and reliability.
- Evaluate the steps for investigating the occurrence of disease.
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Study Materials
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Oswego Outbreak Investigation
NOTE: The following resource was prepared for class use by replicating portions of the Centers for Disease Control and Prevention’s (CDC), “Oswego – An Outbreak of Gastrointestinal Illness Following a Church Supper: Student Guide” (CDC, n.d.), except for the “Questions” section, with the understanding that the CDC document is in the public domain and available for educational use.
Background:
On April 19, 1940, the local health officer in the village of Lycoming, Oswego County, New York, reported the occurrence of an outbreak of acute gastrointestinal illness to the District Health Officer in Syracuse. Dr. A. M. Rubin, epidemiologist-in-training, was assigned to conduct an investigation. When Dr. Rubin arrived in the field, he learned from the health officer that all persons known to be ill had attended a church supper held on the previous evening, April 18. Family members who did not attend the church supper did not become ill. Accordingly, Dr. Rubin focused the investigation on the supper. He completed interviews with 75 of the 80 persons known to have attended, collecting information about the occurrence and time of onset of symptoms, and foods consumed. Of the 75 persons interviewed, 46 persons reported gastrointestinal illness.
Clinical Description:
The onset of illness in all cases was acute, characterized chiefly by nausea, vomiting, diarrhea, and abdominal pain. None of the ill persons reported having an elevated temperature; all recovered within 24 to 30 hours. Approximately 20% of the ill persons visited physicians. No fecal specimens were obtained for bacteriologic examination.
Description of the Supper:
The supper was held in the basement of the village church. Foods were contributed by numerous members of the congregation. The supper began at 6:00 p.m. and continued until 11:00 p.m. Food was spread out on a table and consumed over a period of several hours. Data regarding onset of illness and food eaten or water drunk by each of the 75 persons interviewed [are provided in the Excel “Oswego Line Listing Workbook” (CDC, n.d.)]. The approximate time of eating supper was collected for only about half the persons who had gastrointestinal illness.
Conclusion:
The following is quoted verbatim from the report prepared by Dr. Rubin:
The ice cream was prepared by the Petrie sisters as follows:
On the afternoon of April 17 raw milk from the Petrie farm at Lycoming was brought to boil over a water bath, sugar and eggs were then added and a little flour to add body to the mix. The chocolate and vanilla ice cream were prepared separately. Hershey’s chocolate was necessarily added to the chocolate mix. At 6 p.m. the two mixes were taken in covered containers to the church basement and allowed to stand overnight. They were presumably not touched by anyone during this period.
On the morning of April 18, Mr. Coe added five ounces of vanilla and two cans of condensed milk to the vanilla mix, and three ounces of vanilla and one can of condensed milk to the chocolate mix. Then the vanilla ice cream was transferred to a freezing can and placed in an electrical freezer for 20 minutes, after which the vanilla ice cream was removed from the freezer can and packed into another can which had been previously washed with boiling water. Then the chocolate mix was put into the freezer can which had been rinsed out with tap water and allowed to freeze for 20 minutes. At the conclusion of this both cans were covered and placed in large wooden receptacles which were packed with ice. As noted, the chocolate ice cream remained in the one freezer can.
All handlers of the ice cream were examined. No external lesions or upper respiratory infections were noted. Nose and throat cultures were taken from two individuals who prepared the ice cream.
Bacteriological examinations were made by the Division of Laboratories and Research, Albany, on both ice creams. Their report is as follows: “Large numbers of Staphylococcus aureus and albus were found in the specimen of vanilla ice cream. Only a few staphylococci were demonstrated in the chocolate ice cream.”
Report of the nose and throat cultures of the Petries who prepared the ice cream read as follows: “Staphylococcus aureus and hemolytic streptococci were isolated from nose culture and Staphylococcus albus from throat culture of Grace Petrie. Staphylococcus albus was isolated from the nose culture of Marian Petrie. The hemolytic streptococci were not of the type usually associated with infections in man.”
Discussion as to Source: The source of bacterial contamination of the vanilla ice cream is not clear. Whatever the method of the introduction of the staphylococci, it appears reasonable to assume it must have occurred between the evening of April 17 and the morning of April 18. No reason for contamination peculiar to the vanilla ice cream is known.
In dispensing the ice creams, the same scooper was used. It is therefore not unlikely to assume that some contamination to the chocolate ice cream occurred in this way. This would appear to be the most plausible explanation for the illness in the three individuals who did not eat the vanilla ice cream.
Control Measures: On May 19, all remaining ice cream was condemned. All other food at the church supper had been consumed.
Conclusions: An attack of gastroenteritis occurred following a church supper at Lycoming. The cause of the outbreak was contaminated vanilla ice cream. The method of contamination of ice cream is not clearly understood. Whether the positive Staphylococcus nose and throat cultures occurring in the Petrie family had anything to do with the contamination is a matter of conjecture.
Note: Patient #52 was a child who while watching the freezing procedure was given a dish of vanilla ice cream at 11:00 a.m. on April 18.
Addendum:
Certain laboratory techniques not available at the time of this investigation might prove very useful in the analysis of a similar epidemic today. These are phage typing, which can be done at CDC, and identification of staphylococcal enterotoxin in food by immunodiffusion or by enzyme-linked immunosorbent assay (ELISA), which is available through the Food and Drug Administration (FDA).
One would expect the phage types of staphylococci isolated from Grace Petrie’s nose and the vanilla ice cream and vomitus or stool samples from ill persons associated with the church supper to be identical had she been the source of contamination. Distinctly different phage types would mitigate against her as the source (although differences might be observed as a chance phenomenon of sampling error) and suggest the need for further investigation, such as cultures of others who might have been in contact with the ice cream in preparation or consideration of the possibility that contamination occurred from using a cow with mastitis and that the only milk boiled was that used to prepare chocolate ice cream. If the contaminated food had been heated sufficiently to destroy staphylococcal organisms but not toxin, analysis for toxin (with the addition of urea) would still permit detection of the cause of the epidemic. A Gram stain might also detect the presence of nonviable staphylococci in contaminated food.
Reference
Centers for Disease Control and Prevention. (n.d.). Oswego – An outbreak of gastrointestinal illness following a church supper: Student guide (Case No. 401-303). Retrieved from https://www.cdc.gov/eis/casestudies/xoswego.401-303.student.pdf
Disease surveillance is a necessary public health role. Passive surveillance relies on individuals and local authorities “pushing” information to national agencies who then compile, analyze, and disseminate the information. Unfortunately, significant gaps occur in reporting.
Review your textbook, and the CDC’s National Notifiable Disease Surveillance System (NNDSS). Discuss the strengths of the current surveillance systems, the gaps you identified, and why these gaps occur. Discuss the global challenges of coordinating surveillance between multiple countries and provide an example highlighting the challenges. What could other governments and agencies, such as the World Health Organization and the Centers for Disease Control and Prevention, do to strengthen global disease surveillance systems?
Topic 2 DQ 2 |
Explain the importance of validity and reliability in diagnostic testing or research. Describe how validity relates to sensitivity and specificity in diagnostic testing. Identify a health screen specific to a diagnostic test that is currently being debated regarding its use, recommended ages, or frequency, and discuss how validity and reliability play into this debate. What other factors should you consider when you assess the recommendations for a diagnostic test or screen?
Topic 3: Causal Inference, Confounding, and Bias
Objectives:
- Determine sources of bias within a study design.
- Describe confounding relationships.
- Evaluate the types of causal relationships associated with causation.
- Assess measures of morbidity.
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Differentiate between bias and confounding. Discuss the criteria necessary to establish a factor as a confounder and provide an example applying these criteria. What is one way to adjust for a confounding relationship in the study design or the analysis?
Topic 3 DQ 2 |
Explain the two major types of bias. Identify a peer-reviewed epidemiology article that discusses potential issues with bias as a limitation and discuss what could have been done to minimize the bias (exclude articles that combine multiple studies such as meta-analysis and systemic review articles). What are the implications of making inferences based on data with bias? Include a link to the article in your reference.
Topic 4: Study Designs I
Objectives:
- Compare and contrast randomized trials and cohort studies.
- Differentiate between experimental and observational categories of study designs.
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Multicausality: Confounding Assignment |
Topic 5: Study Designs II
Objectives:
- Compare and contrast case control and cross-sectional studies.
- Evaluate the strengths and weaknesses of study designs used in epidemiological assessments.
- Select methods to evaluate public health programs.
Describe the common characteristics and design of a case-control study. Discuss the three important features when it comes to selecting cases and controls, and identify a situation when one of these might be violated. Discuss the limitations of using questionnaires for determining exposure status and provide examples of alternative strategies for collecting this information in a case-control study Principles of epidemiology.
Discuss the strengths and weaknesses of cross-sectional studies and examples of how they can be “descriptive” or “analytic” study designs Principles of epidemiology. Discuss an example of a disease where survival could influence the association between a possible exposure and the disease when measured with a cross-sectional study. Do not discuss examples used in the textbook.
Topic 6: Measures of Association and Application
Objectives:
- Differentiate between association and causal relationships.
- Determine the relative risk and odds ratio as measures of association.
- Evaluate the utility of the population attributable risk.
- Evaluate the types of causal relationships and associated guidelines for establishing causality.
Creating a 2×2 Contingency Table
Creating a 2×2 contingency table is very useful in calculating a variety of public health measurements, including sensitivity and specificity, negative and positive predictive value, risk ratios, attack rate ratios, and odds ratios.
A 2×2 table is actually a 3×3 table when you include the rows and columns for the totals. If you are setting up a table to measure the sensitivity and specificity of a test or its negative and positive predictive values, you should put the test results on the y-axis (rows) and the actual presence of disease on the x-axis (columns). Principles of epidemiology.
| Disease | No Disease | Total | |
| Test (+) | (a) | (b) | a + b |
| Test (-) | (c) | (d) | c + d |
| Total | a + c | b + d | a + b + c + d |
The highlighted section is where you will enter the data for each corresponding cell. You can set up the table switching the rows and columns but you will generally see them set up in this format with test results on the y-axis and disease on the x-axis.
Setting up a table to measure the association of a risk factor or exposure is similar, with the outcome or disease on the x-axis and the presence of the risk factor or exposure on the y-axis Principles of epidemiology.
| Disease | No Disease | Total | |
| Exposure (+) | (a) | (b) | a + b |
| Exposure (-) | (c) | (d) | c + d |
| Total | a + c | b + d | a + b + c + d |
Note: You can set up the table differently but you will need to be cognizant of which numbers you are putting in your numerator and denominator for the measure you are calculating. For example:
| Exposure (+) | Exposure (-) | Total | |
| No Disease | (b) | (d) | b + d |
| Disease | (a) | (c) | a + c |
| Total | a + b | b + c | a + b + c + d |
Differentiate between association and causation using the causal guidelines. Discuss which of the guidelines you think is the most difficult to establish Principles of epidemiology. Discuss the four types of causal relationships and use an example not listed in the textbook to describe each relationship.
Topic 6 DQ 2 |
Explain the difference between relative risk, attributable risk, and population attributable risk. Provide an example (not from the textbook) of how each type of risk is used in epidemiology. How would you propose using population attributable risk to advocate for a health policy or intervention relative to your health interest?
Topic 7: Applying Epidemiology to Policy
Objectives:
- Apply epidemiological methods to the breadth of settings and situations in public health practice.
- Discuss the means by which social inequities, and racism undermine health and create challenges to achieving health equity at organizational, community and societal levels Principles of epidemiology.
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Epidemiological methods are used in a variety of public health areas (including infectious disease, chronic disease, and social health) and settings (including the community, schools, and the workplace). Epidemiological methods are used to assess, describe, analyze, and make comparisons of populations to inform evidence-based practices, policies, and interventions. Propose a study based on the methods you have learned thus far designed to investigate an association within one of the public health areas listed (infectious disease, chronic disease, or social health) and the methods you would apply. Discuss and define the risk factor or exposure that is being assessed, the method of comparison that is used, and the setting or situation (community, school, workplace, etc.) your study would look to address. Consider the concepts of causal inference, measures of association, and study design Principles of epidemiology.
Race is often used as a descriptor of disease burden and helps us to determine where health disparities exist in order to address them, which is important. It is helpful to differentiate between race as a descriptor and race as a risk factor. Think about institutional racism and its influence on health. Consider the factors related to race and ethnicity that might be influencing disease status more than the genetics of race when answering this discussion question.
Consider the following statement: “Race is not a risk factor and should not be used in public health data collection.” Discuss the ethical and public health implications of this statement. When might collecting data on race perpetuate institutional racism leading to health disparities and when is it necessary to improve public health? Provide support and examples for your answer. Principles of epidemiology Consider ethical issues related to respect for persons, beneficence, and justice as described in “The Belmont Report.”
Topic 8: Environment and Genetics
Objectives:
- Discuss how genetic and environmental factors interact in causing disease.
- Explain the biological and genetic factors that affects a population’s health. Principles of epidemiology
Complete the Final Exam. This is a cumulative exam.
Attempt Start Date: 20-Feb-2020 at 02:00:00 AM
Maximum Points: 100.0
Total Number of Questions: 20
Attempts: 1
One method to investigate gene-environment interactions is to study monozygotic twins. Identify an example of a twin study not listed in the textbook used to examine the gene-environment interaction of a specific disease or condition. Briefly summarize the gene-environment interaction investigated, the methods, and the results. What are other possible methods for studying gene-environment interactions as they relate to improving population health? Principles of epidemiology
Using the CDC Wonder website, set the query criteria for pancreatic cancer for the United States as illustrated below. Compare the rates by race for Wisconsin and Colorado. Discuss possible biological, genetic, and environmental reasons for differences. What are potential social determinants that contribute to the disparity presented between the two states?
Use this query upon entering the CDC Wonder website:
Select “Cancer Statistics” under the Wonder Systems tab
Select “Cancer Incidence 1999 – 2013” and click “Data Request” Principles of epidemiology
Organize table layout:
- Group results by 1. States and 2. Race (leave the rest of the group options as “None”)
- Measures – click “Count” (default) and “Age Adjusted Rates”
Select location – select “States” and “The United States”
Select year and demographics
- Year – 2014
- Sex – All genders
- Age groups – All ages
- Ethnicity – All ethnicities
- Race – All races
Select cancers of interest – select “Pancreas”
Other options – keep default settings Principles of epidemiology