Overview of Epidemiology

1. Overview of Epidemiology Greg Evans, PhD, MPH Institute for Biosecurity

2. Learning Objectives • Define bioterrorism epidemiology • Describe epidemiological approach to understanding disease etiology • Recognize difference between incidence and prevalence • Distinguish between the stages of the disease process

3. Biological and Chemical Epidemiology The study of the distribution and determinants of diseases resulting from a biological or chemical attack

4. Sources of Epidemiologic Clues to a Disease Outbreak • Clinician’s office or medical clinic • Emergency room • Laboratory • Veterinary Clinic • Pharmacy

5. Epidemiologic Approach to Understanding Disease Etiology • Descriptive epidemiology - identifying associations of disease in relation to • Time • Place • Persons

6. Epidemiologic Approach to Understanding Disease Etiology • Analytic epidemiology • Identify associations of disease with possible etiologic factors (chemical release, biological agent) • Further refine and test hypotheses regarding etiology

7. Problems Investigating the Causes of Disease • Specific agent might not be known • Location of agent release might not be known • Signs and symptoms might not differentiate disease • More than one agent might be used • Time of agent release might not be known • Latency period might not be known • Latency is not the same for all people

8. Host Agent Environment Epidemiologic Triad of Disease

9. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

10. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

11. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

12. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

13. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

14. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

15. Modes of Transmission • Direct • Contact • Droplets • Indirect • Airborne • Vehicle-borne • Vector-borne • Mechanical • Biologic Host Environment Agent

16. Factors That May Be Associated With Disease

17. Factors That May Be Associated With Disease

18. Factors That May Be Associated With Disease

19. Factors That May Be Associated With Disease

20. Factors That May Be Associated With Disease

21. Factors That May Be Associated With Disease

22. Factors That May Be Associated With Disease

23. Factors That May Be Associated With Disease

24. Factors That May Be Associated With Disease

25. Factors That May Be Associated With Disease

26. Factors That May Be Associated With Disease

27. Outcome Cure Control Disability Death Healthy Disease Symptoms Seek Diagnosis Treatment Onset Care The Natural History of Disease

28. Outcome Cure Control Disability Death Healthy Disease Symptoms Seek Diagnosis Treatment Onset Care The Natural History of Disease

29. Outcome Cure Control Disability Death Healthy Disease Symptoms Seek Diagnosis Treatment Onset Care The Natural History of Disease

30. Outcome Cure Control Disability Death Healthy Disease SymptomsSeek Diagnosis Treatment OnsetCare The Natural History of Disease

31. Outcome Cure Control Disability Death Healthy Disease SymptomsSeekDiagnosis Treatment OnsetCare The Natural History of Disease

32. Conducting a Field Investigation

33. Conducting a Field Investigation • When possible, collect information that describes: • When people became ill • Where they acquired the disease • Characteristics of the people

34. Conducting a Field Investigation • When descriptive information does not readily indicate risk factors, analytical methods will be required: • Determining rates and comparing them • Comparing ill and well or • Comparing exposed and unexposed • Most analysis should be done in the field

35. Steps in Conducting a Field Investigation of a Bioterrorist Event • Determine if there is an increase in the occurrence of disease • Confirm the diagnosis of disease • Determine definition of a case • Analyze the data in terms of time, place, and person • Determine who is at risk for becoming ill

36. Steps in Conducting a Field Investigation of a Bioterrorist Event • Develop an hypothesis that explains the specific exposure that caused disease • Test hypothesis using statistics • Compare hypothesis with known facts • Execute control and prevention measures • Plan a more systematic study • Prepare a written report Adapted from MB Gregg, Field Epidemiology

37. Determine If There Is an Increase in the Occurrence of Disease • Initial indication of an increase might be syndromic only • Might need to check hospital and clinic records for increase in symptoms • Might need to telephone a sample of physicians • Might require a rapid community survey • Might be difficult to distinguish between a disease outbreak related to bioterrorism and one from other causes

38. Confirm the Diagnosis of Disease • Frequently requires laboratory techniques • Can not always wait for confirmation before starting treatment and prophylaxis • Might only require laboratory confirmation of first few cases before relying solely on signs and symptoms

39. Determine Definition of a Case • Use signs and symptoms or simple, rapid laboratory techniques • At this point, more important to include all possible cases (high sensitivity) • Use simple case definition to initiate immediate treatment

40. Analyze the Data in Terms of Time, Place, and Person to Determine Who is at Risk • When did patients first start becoming ill • Where were they when they became ill • What were their activities prior to becoming ill and where were they performing these activities • What are the characteristics of the ill person

41. Develop an Hypothesis That Explains the Specific Exposure That Caused Disease • The origin of the specific exposure might not be obvious • Can be the most challenging aspect of the investigation

42. Test Hypothesis Using Statistics • Statistics provide a set of tools that help an epidemiologist reduce the role of chance in hypothesis testing • Statistics can not substitute for an epidemiologists’ review of all the evidence before he decides on an intervention plan

43. Compare Hypothesis With Known Facts • Is the hypothesis in agreement with laboratory, clinical, and other epidemiological evidence • Might need to consult other scientific disciplines (e.g. Medicine, Biology, Environmental Science, Laboratory Science)

44. Execute Control and Prevention Measures • Important to get to this step as quickly as possible, particularly in a case of a highly lethal agent • Sometimes must make decisions that rely on incomplete information • These decisions must be continually reviewed as new information is obtained

45. Plan a More Systematic Study • As control measures are initiated, additional questions will arise that will require additional studies • These studies should use the most applicable epidemiological study methods available

46. Prepare a Written Report • A document for action • A record of performance • A document for potential medical/legal issues • A systematic review of the investigational methods that might suggest additional analysis • A document that will help others investigate and control future bioterrorist attacks