Bringing Change by Measuring Impact

Health Information Management and Applied Epidemiology for Health Care Workers in South Africa

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Module 6

Introduction to Applied Epidemiology: Frequency & Distribution of Disease

Learning Objectives

At the end of Module 6, you will be able to:

  • Define, calculate, and interpret measures of frequency: prevalence, cumulative incidence, and incidence rate.
  • Explain how the concepts of person, place, and time are used in epidemiology to describe the distribution of disease in a population (descriptive epidemiology).
  • Summarise the principles for comparing disease risk between two groups, and establishing associations (analytic epidemiology); and define, calculate, and interpret measures of association: relative risk and odds ratio.
  • Describe the purpose of an outbreak investigation, the terminology used, and the steps to be followed.
  • Demonstrate development and use of line lists and epidemic curves in outbreak investigations.
  • Explain different types of surveillance (active and passive), different surveillance approaches and methods, and South Africa’s system for surveillance of notifiable conditions.
  • Evaluate routine data for evidence of trend, and detection of outbreaks.
  • Define the various measures of test performance (sensitivity, specificity), and interpret their implications for testing algorithms (e.g., confirmatory testing).

Welcome to Module 6, which will introduce us to the basics of Applied Epidemiology. This includes exploring the meanings of incidence and prevalence, and how to calculate them; how to describe distribution of a disease in a population (person, place, and time); and how to define and calculate measures of association (relative risk and odds ratio). We will also learn about the steps to follow in an outbreak investigation, including surveillance approaches and methods.

Pre-test (10 minutes)

Part 1: What Is Applied Epidemiology? (5 minutes)

Part 2: Measuring Disease Frequency (40 minutes)

Part 3: Descriptive Epidemiology (15 minutes)

Part 4: Measuring Association (45 minutes)

Part 5: Outbreak Investigations (45 minutes)

Part 6: Line Lists & Epidemic Curves (15 minutes)

Part 7: Disease Surveillance (25 minutes)

Part 8: Performance of Diagnostic Test (40 minutes)

  • Summary

    In this module, we introduced the basic concepts of applied epidemiology, specifically focusing on frequency and distribution of disease.

    We started in Part 1 by defining applied epidemiology, which is how we apply or use the tools of epidemiology to prevent and control health problems.

    In Part 2, we learned how to measure how often disease occurs by learning how to define and calculate prevalence and incidence rates. We learned about how prevalence and incidence relate to and affect each other. We also learned about other types of rates that we can calculate, such as the birth rate, infant mortality rate, and maternal mortality ratio.

    In Part 3, we learned how to describe the distribution of disease in a population using person, place, and time (also known as descriptive epidemiology).

    Next, we learned how to measure association, which is a way to quantify the relationship between exposure and disease. We looked at how different exposures might lead to different diseases, then learned how to calculate relative risk (RR) and odds ratios (OR).

    We then looked at outbreak investigations by learning the terminology we should use, and the steps we should follow to conduct an outbreak investigation:

    1. Verify the diagnosis.
    2. Confirm that an outbreak has occurred.
    3. Prepare for fieldwork
    4. Establish a case definition, and expand case finding (identify and count cases).
    5. Describe the outbreak.
    6. Take immediate control measures.
    7. Generate a hypothesis (an idea or theory that leads to further study or discussion).
    8. Test the hypothesis.
    9. Take further action (improve or expand interventions).
    10. Document and communicate findings.

    In Part 6, we learned how to use line lists and epidemic curves in an outbreak investigation as a means of better describing, organising, and displaying what is happening during an outbreak investigation.

    In order to detect these outbreaks, we need to use surveillance. In Part 7, we learned about both passive and active surveillance. We also learned about how to evaluate surveillance systems, and about measures of test performance, including reliability, validity, sensitivity, and specificity.

    All of this knowledge has prepared us well to continue on to Module 7, which continues with the basics of applied epidemiology, but with a focus on determinants of disease, research, and study design.

Post-test (10 minutes)

  • References

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