Introduction to Epidemiology: Measuring Health and Disease

1. Module 2:Fundamentals of Epidemiology Measuring Health and Disease Developed through the APTR Initiative to Enhance Prevention and Population Health Education in collaboration with the Brody School of Medicine at East Carolina University with funding from the Centers for Disease Control and Prevention

2. Acknowledgments This education module is made possible through the Centers for Disease Control and Prevention (CDC) and the Association for Prevention Teaching and Research (APTR) Cooperative Agreement, No. 5U50CD300860. The module represents the opinions of the author(s) and does not necessarily represent the views of the Centers for Disease Control and Prevention or the Association for Prevention Teaching and Research. APTR wishes to acknowledge the following individuals that developed this module: Kristina Simeonsson, MD, MSPH Department of Public Health Brody School of Medicine at East Carolina University Jeffrey Bethel, PhD Department of Public Health Brody School of Medicine at East Carolina University

3. Presentation Objectives Define epidemiology and recognize some of its uses Interpret distribution of disease according to person, place, and time Calculate measures of disease occurrence and severity

4. What is epidemiology, really? • Study of health and disease among populations • Basic science of public health • What causes disease? • How does disease spread? • What prevents disease? • How to control disease?

5. Uses of Epidemiology • Identify etiology and risk factors • Determine the extent of disease in a population • Study natural history and prognosis • Evaluate existing and new preventive and therapeutic measures/modes of healthcare delivery • Provide foundation for developing public policy and regulatory decisions

6. Epidemiology The study of the distribution and determinants of diseases or other health-related outcomes in populations and the application of this study to control health problems

7. Distributionof Disease • Analysis of disease patterns • Person • Place • Time

8. Acute Hepatitis BPerson Source: National Notifiable Diseases Surveillance System, 2006.

9. Acute Hepatitis BPlace Incidence of acute hepatitis B, by county—United States, 2007 Source: National Notifiable Diseases Surveillance System, 2007.

10. Acute Hepatitis BTime

11. Measures of Morbidity and Mortality • Counts • Proportions • Prevalence • Rates • Incidence • Attack rate • Mortality rate • Case fatality rate • Infant mortality rate

12. Counts Measure of disease frequency Number of cases or other health outcome being studied

13. CholeraNumber of reported cases, 2008 CDC, MMWR Summary of Notifiable Diseases, US 2008

15. Prevalence • Answers the question: How common is it? • Burden of disease in a population • A slice through the population at a point in time at which it is determined who has the disease and who does not • Often stated as a percentage (i.e. per 100)

16. Prevalence # of cases of a disease present in the population at a specified time # of persons in the population at that specified time

17. Prevalence • Don’t know when disease developed or the duration • Numerator is a mix of people with different durations of disease • Do not have a measure of risk • Prevalence is appropriate measure of the burden of a relatively stable chronic condition • Diabetes • Hypertension • Useful for allocating health resources

18. Obesity Trends*Among US Adults(*BMI≥30, or about 30 lbs. overweight for 5’4” person) 1990 1999 2009 No Data <10% 10%–14% 15%–19% 20%–24% 25%–29% ≥30% CDC, BRFSS, 1990, 1999, 2009

19. Age-adjusted Percentage of U.S. Adults who had Diagnosed Diabetes 1994 1999 2009 CDC’s Division of Diabetes Translation. National Diabetes Surveillance System

20. Incidence • Measures change from non-disease to disease • Can provide a measure of risk • Also known as incidence rate • Often stated per 100,000 population per year

21. Incidence # of new cases of a disease during a specified period of time Total number of people at risk during that period of time

22. Incidence Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute, 2010

23. Incidence Department of Health and Human Services, Centers for Disease Control and Prevention, and National Cancer Institute, 2010

24. Incidence • Monitor changes over time • Comparisons between groups • Age-specific rates • Sex-specific rates • Goal setting • Healthy People 2020 Objectives

28. Attack Rate • Similar to incidence (rate) • Used when nature of the disease is such that population is observed for a short time period, often as a result of specific exposure • Foodborne outbreaks • Compares the risk of disease in groups with different exposures

29. Attack Rate # of people who ate potato salad who developed gastroenteritis Total # of people who ate potato salad

30. Relationship Between Incidence and Prevalence • Prevalence = incidence x duration of disease • An increased prevalence may reflect • Increased risk of disease in the population • Increased incidence • Increased duration of illness • Fewer deaths from the disease (increased survival) • Fewer responses to treatment

31. Relationship Between Incidence and Prevalence • An increased prevalence may reflect • Increased risk of disease in the population • Increased incidence • An increased prevalence may also reflect • Increased duration of illness • Fewer deaths from the disease (increased survival) • Fewer responses to treatment

32. Relationship between Incidence and Prevalence

33. Relationship between Incidence and Prevalence

34. Relationship between Incidence and Prevalence

35. Relationship between Incidence and Prevalence

36. AIDS Incidence, Deaths, and Prevalence

37. Measures of Mortality Mortality Rate Case Fatality Rate Infant Mortality Rate

38. Mortality Rate # of all deaths in one year # persons in the population at midyear

41. Case Fatality Rate # of persons dying during a specified period after disease onset or diagnosis Total # of people with the specified disease

42. Case Fatality Rate for Avian Influenza A/H5N1 309 deaths from H5N1 CFR 59% 522 cases of H5N1 WHO website, accessed 2/25/2011

43. Mortality Rate versus Case Fatality Rate Mausner & Kramer, 1985

44. National Cancer Institute; A Snapshot of Pancreatic Cancer

45. Infant Mortality Rate # of deaths under one year of age during a specified time interval # of live births reported during the same time period Expressed per 1,000

47. Summary • Epidemiology is the basic science of public health • Count, describe, divide, compare • Must use rates to compare groups and assess risk • Primary measures of disease occurrence • Incidence • Prevalence • Primary measure of disease severity • Case fatality rate

48. Collaborating Institutions Center for Public Health Continuing Education University at Albany School of Public Health Department of Community & Family Medicine Duke University School of Medicine

49. Advisory Committee Mike Barry, CAE Lorrie Basnight, MD Nancy Bennett, MD, MS Ruth Gaare Bernheim, JD, MPH Amber Berrian, MPH James Cawley, MPH, PA-C Jack Dillenberg, DDS, MPH Kristine Gebbie, RN, DrPH Asim Jani, MD, MPH, FACP Denise Koo, MD, MPH Suzanne Lazorick, MD, MPH Rika Maeshiro, MD, MPH Dan Mareck, MD Steve McCurdy, MD, MPH Susan M. Meyer, PhD Sallie Rixey, MD, MEd Nawraz Shawir, MBBS

50. APTR • Sharon Hull, MD, MPH President • Allison L. Lewis Executive Director • O. Kent Nordvig, MEd Project Representative