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EPIDEMIOLOGY Introduction and Disease Transmission

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  1. EPIDEMIOLOGYIntroduction and Disease Transmission Sue Lindsay, Ph.D., MSW, MPH Division of Epidemiology and Biostatistics Institute for Public Health San Diego State University

  2. Epidemiology The study of patterns of health, disease, and injury in human populations and the application of this study to the control of health problems

  3. ASPH Ten Epidemiology Competencies Upon Graduation, a student with an MPH should be able to: • Identify key sources of data for epidemiologic purposes 2. Identify the principles and limitations of public health screening programs 3. Describe a public health problem in terms of magnitude, person, time, and place 4. Explain the importance of epidemiology for informing scientific, ethical, economic, and political discussions of health issues

  4. ASPH Ten Epidemiology Competencies Upon Graduation, a student with an MPH should be able to: • Comprehend basic ethical and legal principles pertaining to the collection, maintenance, use, and dissemination of epidemiologic data. • Apply the basic terminology and definitions of epidemiology. • Calculate basic epidemiology measures. • Communicate epidemiologic information to lay and professional audiences.

  5. ASPH Ten Epidemiology Competencies Upon Graduation, a student with an MPH should be able to: • Draw appropriate inferences from epidemiologic data. • Evaluate the strengths and limitations of epidemiologic reports.

  6. Underlying Assumptions • Illness and disease are not randomly distributed in human populations • Each human being has characteristics that either predispose toward illness, or protect from illness. • Communities and neighborhoods also have characteristics that either predispose toward, or protect from illness. • These characteristics are identifiable and modifiable

  7. As Medical Detectives Epidemiologists Must Find: • Who? • What? • Where? • When? • Why? • How?

  8. The Five Objectives of Epidemiology 1. To identify the cause(s) of a disease and the risk factors for that disease. • How is the disease or condition transmitted or acquired? Are there sub-groups of the population at high risk for the disease? 2. To determine the extent of the disease found in a community or population - surveillance • What is the burden of the disease or condition?

  9. The Five Objectives of Epidemiology 3. To study the natural history and prognosis of the disease • Severity, lethality, duration, survivorship 4. To evaluate existing and new preventive and therapeutic measures as well as modes of health care delivery • Does screening for disease impact outcome?

  10. The Five Objectives of Epidemiology 5. To provide the foundation for developing public health policy and regulatory decisions • How do environmental problems impact human health?

  11. Epidemiologic Areas of Study • Observational Epidemiology • Natural Experiments • Experimental Epidemiology

  12. Historical Examples of Epidemiology in Practice

  13. The Story of Smallpox • Major worldwide epidemic in the late 1700’s • Known immunity from re-infection among survivors • “Variolation”: early attempts at control were done by using infected smallpox pus and tissue to “variolate” healthy people

  14. The Story of Smallpox • Dairy Maids - young women who milked cows got mild disease known as “Cowpox” • During smallpox outbreaks, dairy maids did not develop smallpox • Edward Jenner (born 1749), physician practicing in England believed cowpox could protect against smallpox

  15. The Story of Smallpox • 1778: Jenner decides to test his hypothesis • Innoculates an 8 year old “volunteer” James Phipps with cowpox material from a dairy maid • Six weeks later Jenner exposes the boy to a smallpox infection • Smallpox did not infect the boy

  16. The First Vaccination

  17. The Story of Cholera • Cholera was a major public health problem in England in the mid-19th century • First week of September 1854: 600 Deaths among people living near Broad Street in London

  18. The Story of Cholera • John Farr, Registrar General • John Farr believed the disease was transmitted by a cloud or “miasma” clinging low to the earth • He hypothesized that greater altitude would be protective against cholera

  19. Deaths from Cholera in 10,000 Inhabitants by Elevation Above Sea Level, London 1848-1849

  20. The Story of Cholera • John Snow, physician to Queen Victoria • Believed cholera was transmitted by contaminated water • Public water companies transported water supply from polluted parts of the Thames River. • The Lambeth Water Company moved their water intake upriver towards non-polluted water

  21. The Story of Cholera • John Snow hypothesized that death rates would be lower in households buying water from the Lambeth Company • 1854: Conducted a house to house survey • Number of deaths/household • Water company that supplied the household

  22. Deaths From Cholera Per 10,000 Houses By Source of Water Supply

  23. Deaths From Cholera Per 10,000 Houses By Source of Water Supply

  24. 1952

  25. Overweight and Obesity1960-2000

  26. The Epidemiologic Approach • How does the epidemiologist identify public health problems and design interventions? • Frequency of health and disease • Patterns of disease by age • Patterns of disease by geography • Patterns of disease by race/ethnicity • Patterns of disease by gender

  27. Frequency of Health and DiseaseTen Leading Causes of Death in the United States, 1900 and 1997

  28. Patterns of Disease by AgeLife Expectancy At Birth and Age 65, By Race and Sex, United States, 1900, 1950, 1996

  29. Patterns of Disease by Geography

  30. Adult/Adolescent AIDS Rates per 100,000 White Population Reported in 1999 6.1 1.3 7.0 1.2 3.1 7.7 3.0 NH 3.5 2.5 1.9 2.4 13.1 MA 15.4 2.8 3.3 RI 7.1 3.0 6.3 CT 10.3 3.6 13.1 NJ 8.9 3.5 7.0 5.5 7.6 DE 11.7 17.7 7.7 3.6 MD 7.3 5.8 6.9 6.5 5.8 DC 70.9 3.7 8.6 20.6 6.7 3.9 6.2 Rate per 100,000 8.7 <5 7.9 7.0 5.5 5-9.9 10+ 13.1 10.1 <5 cases * * 19.6 US rate =9.0 21.1 N=14,813 † Includes cases with unknown state of residence †

  31. 45.6 * * * * 37.9 55.5 * * 29.7 * 180.3 MA 173.0 * 36.8 RI 81.2 29.1 131.1 20.8 CT 82.4 54.3 NJ 147.6 23.6 63.0 29.3 89.5 DE 107.4 70.3 36.9 32.1 MD 114.7 36.9 56.7 56.4 41.0 DC 266.3 45.4 61.1 74.5 * 18.5 25.1 Rate per 100,000 84.0 <50 39.6 77.7 36.5 50-99 100+ 67.4 56.0 * <5 cases * 182.1 US rate =84.2 N=21,730 27.1 Includes cases with unknown state of residence † Adult/Adolescent AIDS Rates per 100,000 Black Population Reported in 1999

  32. 15.3 * * * * 15.7 31.8 NH 60.7 * 14.9 * 124.5 MA 127.3 * 15.9 RI 60.0 14.8 108.6 CT 89.2 17.6 24.7 NJ 43.6 20.0 19.3 12.2 32.3 DE 42.7 21.9 16.3 * MD 23.5 22.6 16.2 23.4 29.2 DC 112.2 25.6 32.5 25.4 6.6 7.8 32.3 * Rate per 100,000 <20 57.9 19.3 25.8 20-49.9 50+ 17.2 20.6 <5 cases * * US rate =34.6 43.2 P.R. 41.9 N=8,967 † 7.1 † Includes cases with unknown state of residence Adult/Adolescent AIDS Rates per 100,000 Hispanic Population Reported in 1999

  33. Proportion of AIDS Cases, by Race/Ethnicity and Year of Report,1985-1999, United States 70 White, not Hispanic 60 s e s 50 a C Black, not Hispanic f 40 o t n 30 e Hispanic c r e P 20 American Indian/ 10 Asian/Pacific Islander Alaska Native 0 1985 1987 1989 1991 1993 1995 1997 1999 Year of Report

  34. AIDS Cases Reported in 1999 and Estimated 1999 Population, by Race/Ethnicity, United States AIDS Cases Population N=46,400* N=277,200,000 71% 32% <1% 1% 1% 47% 4% 19% 13% 12% White, not Hispanic Asian/Pacific Islander Black, not Hispanic American Indian/ Alaska Native Hispanic *Includes 120 persons with unknown race/ethnicity

  35. Noteworthy Examples of Epidemiologic Investigations • Tampons and Toxic Shock Syndrome • Legonnaire’s Disease • Low Level Ionizing Radiation and Leukemia • Hormone replacement therapy and heart attack, stroke, blood clots, breast cancer, reduced risk of colorectal cancer

  36. Noteworthy Examples of Epidemiologic Investigations • Passive Smoking • Agent Orange • Acquired Immune Deficiency Syndrome (AIDS) • The Effect of DES on Off-Spring • Severe Acute Respiratory Syndrome (SARS) Asia 2003, 12+ countries, 8,098 sick, 774 died • Avian Influenza (Bird Flu)

  37. Disease Transmission

  38. Vector The Epidemiologic Triad Host Agent Environment

  39. An Example of The Epidemiologic Triad Host (Person) Environment (Contaminated Water) Agent (Bacterium) Vector (Mosquito)

  40. Factors Which Influence Health and Disease in Humans • Biological • Physical • Chemical and Environmental • Genetics • Nutrition • Immunology

  41. Age Sex Race Occupation Religion Customs Family Background Previous Diseases Immune Status Genetic Profile Marital Status Host Characteristics

  42. Biologic Bacteria, Virus Chemical Poison, Alcohol,Smoke Physical Trauma, Radiation, Fire Nutrition Diet, Low / Excess Caloric Intake Types of Agents

  43. Temperature Humidity Altitude Crowding Housing Neighborhoods Violence Water Milk Food Radiation Air Pollution Noise Public health infrastructure Environmental Factors

  44. Modes of Disease Transmission • Direct: Person to Person Contact • Indirect: • Vehicle borne • Vector borne • Single exposure • Multiple exposures • Continuous exposure