90110 pp tx_ch03


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90110 pp tx_ch03

  1. 1. Epidemiology: The Study of Disease, Injury, and Death in the Community Chapter 3
  2. 2. Introduction <ul><li>Epidemiology = population medicine </li></ul><ul><li>Epidemiologists concerned with course of disease in a population </li></ul><ul><li>Collect information about disease status of a community </li></ul><ul><ul><li>How many people are sick? Who is sick? When did they become sick? Where do they live? </li></ul></ul><ul><li>Data can be used to prevent disease outbreaks or determine effectiveness of prevention effort </li></ul>
  3. 4. Definitions <ul><li>Epidemiology: study of distribution and determinants of health-related states or events in specified populations </li></ul><ul><li>Epidemic: unexpectedly large number of cases of an illness, specific health-related behavior or event, in a particular population </li></ul><ul><li>Endemic: disease that occurs regularly in a population as a matter of course </li></ul><ul><li>Pandemic: outbreak over wide geographic area </li></ul>
  4. 5. The Epidemics?
  5. 7. The Importance of Rates <ul><li>Rates allow for comparison of outbreaks at different times or in different places </li></ul><ul><li>Cases: people afflicted (those who are sick) </li></ul><ul><li>Rates: number of events in a given population over a given period of time or given point in time </li></ul><ul><ul><li>Natality (birth), morbidity (sickness), mortality or fatality (death) rates </li></ul></ul><ul><li>Population at Risk: those susceptible to particular disease or condition </li></ul>
  6. 8. Morbidity Rates <ul><li>Incidence rate: number of new health-related events or cases of a disease in a population exposed to that risk during a particular period of time, divided by total # in same population </li></ul><ul><li>Prevalence rate: number of new and old cases in a given period of time, divided by total # in that population </li></ul><ul><li>Attack rate: incidence rate calculated for a particular population for a single disease outbreak; expressed as a percentage </li></ul>
  7. 10. <ul><li>Incidence rates important to study of acute diseases </li></ul><ul><ul><li>Acute disease: lasts three months or less </li></ul></ul><ul><li>Prevalence rates useful for study of chronic diseases </li></ul><ul><ul><li>Chronic disease: last longer than three months </li></ul></ul><ul><li>Incidence and prevalence rates expressed as crude or specific </li></ul>Incidence, Prevalence, and Attack Rates
  8. 11. Incidence, Prevalence, and Attack Rates
  9. 12. Crude and Age-Adjusted Rates <ul><li>Crude rates: denominator includes the total population </li></ul><ul><ul><li>Crude birth rate: # of live births in given year, divided by midyear population </li></ul></ul><ul><ul><li>Crude death rate: # of deaths in given year from all causes, divided by midyear population </li></ul></ul><ul><li>Age-adjusted rates: used to make comparisons of relative risks across groups and over time when groups differ in age structure </li></ul>
  10. 14. Crude and Age-Adjusted Rates
  11. 15. Specific Rates <ul><li>Measure morbidity and mortality for particular populations or diseases </li></ul><ul><li>Case fatality rate: percentage of cases of a particular disease that result in death </li></ul><ul><li>Proportionate mortality ratio: percentage of overall mortality in a population that is attributable to a particular cause </li></ul>
  12. 16. Important Rates in Epidemiology
  13. 17. Reporting of Birth, Deaths, and Diseases <ul><li>Physicians, clinics, and hospitals required to report births, deaths, and notifiable diseases </li></ul><ul><ul><li>Notifiable diseases: infectious diseases in which health officials request or require reporting </li></ul></ul><ul><ul><ul><li>Can become epidemics </li></ul></ul></ul><ul><ul><ul><li>Health officials maintain weekly records </li></ul></ul></ul><ul><li>Various challenges to maintaining accurate data </li></ul>
  14. 18. Notifiable Disease Scheme
  15. 19. Standardized Measurements of Health Status of Populations <ul><li>Mortality statistics most reliable measure of population health status </li></ul><ul><ul><li>Easier to track death than illness </li></ul></ul><ul><li>Life expectancy: average number of years a person from a specific cohort is projected to live from a given point in time </li></ul><ul><li>Years of potential life lost (YPLL): number of years lost when death occurs before one’s life expectancy </li></ul>
  16. 20. Life Expectancy Figures
  17. 21. Years of Potential Life Lost <ul><li>Subtract person’s age at death from his or her life expectancy </li></ul><ul><li>Difficult to determine because life expectancy changes at different ages </li></ul><ul><li>Weighs death of young person as counting more than death of old </li></ul>
  18. 23. Sources of Standardized Data <ul><li>Various valid sources have specific value and usefulness to those in public health </li></ul><ul><ul><li>U.S. Census </li></ul></ul><ul><ul><ul><li>Taken every 10 years </li></ul></ul></ul><ul><ul><ul><li>Enumeration of the population </li></ul></ul></ul><ul><ul><ul><li>More complex now </li></ul></ul></ul><ul><ul><ul><ul><li>Gathers data on race, age, income, employment, education, and other social indicators </li></ul></ul></ul></ul>
  19. 24. <ul><ul><li>Statistical Abstract of the United States </li></ul></ul><ul><ul><ul><li>Book published annually by Bureau of Census </li></ul></ul></ul><ul><ul><ul><li>Summary of statistics on social, political, and economic organization of the United States </li></ul></ul></ul><ul><ul><li>Monthly Vital Statistics Report </li></ul></ul><ul><ul><ul><li>Vital statistics are summaries of records of major life events: birth, death, marriage, divorce </li></ul></ul></ul><ul><ul><ul><li>Published by National Center for Health Statistics under the CDC </li></ul></ul></ul><ul><ul><ul><li>Also calculates death rates by race and age </li></ul></ul></ul>Sources of Standardized Data (ctd)
  20. 25. <ul><ul><li>Morbidity and Mortality Weekly Report (MMWR) </li></ul></ul><ul><ul><ul><li>Prepared by CDC from state health department reports </li></ul></ul></ul><ul><ul><ul><li>Reports morbidity and mortality data by state and region of U.S. </li></ul></ul></ul><ul><ul><ul><li>Reports outbreaks of disease, environmental hazards, unusual cases, or other public health problems </li></ul></ul></ul>Sources of Standardized Data (ctd)
  21. 30. National Health Surveys <ul><li>National Health Survey Act of 1956 authorized continuing survey of amount, distribution, and effects of illness and disability in the U.S. </li></ul><ul><li>Three types of surveys </li></ul><ul><ul><li>Health interviews of people </li></ul></ul><ul><ul><li>Clinical tests, measurements, and physical examinations </li></ul></ul><ul><ul><li>Surveys of places where people receive medical care </li></ul></ul>
  22. 31. Some National Health Surveys <ul><li>National Health Interview Survey (NHIS) </li></ul><ul><ul><li>Conducted by NCHS </li></ul></ul><ul><ul><li>Questions respondents about their health </li></ul></ul><ul><li>National Health and Nutrition Examination Survey (NHANES) </li></ul><ul><ul><li>Assesses health and nutrition status through mobile examination center </li></ul></ul><ul><li>Behavioral Risk Factor Surveillance System (BRFSS); National Health Care Survey (NHCS) </li></ul>
  23. 32. Epidemiological Studies <ul><li>Investigations carried out when disease or death occurs in unexpected or unacceptable numbers </li></ul><ul><li>Descriptive studies </li></ul><ul><ul><li>Describe epidemics with respect to person, place, and time </li></ul></ul><ul><li>Analytic studies </li></ul><ul><ul><li>Aimed at testing hypotheses </li></ul></ul>
  24. 33. Descriptive Studies <ul><li>Who? </li></ul><ul><ul><li>Case count, followed by who is ill (children, men, women, race, etc.) </li></ul></ul><ul><li>When? </li></ul><ul><ul><li>Time of onset for each case </li></ul></ul><ul><ul><li>Epidemic curves created </li></ul></ul><ul><li>Where? </li></ul><ul><ul><li>Determine residential address and travel history </li></ul></ul>
  25. 34. Epidemic Curves <ul><li>Graphic display of the cases of disease according to the time or date of onset of symptoms </li></ul><ul><li>Secular, seasonal, and single epidemic curves </li></ul><ul><li>Single epidemic curves </li></ul><ul><ul><li>Point source epidemic curve </li></ul></ul><ul><ul><li>Propagated epidemic curve </li></ul></ul>
  26. 35. Secular Epidemic Curve
  27. 36. Seasonal Epidemic Curve
  28. 37. Point Source Epidemic Curve
  29. 38. Propagated Epidemic Curve
  30. 39. Analytic Studies <ul><li>Test hypotheses about relationships between health problems and possible risk factors </li></ul><ul><ul><li>Observational studies: investigator observes natural course of events, noting exposed vs. unexposed and disease development </li></ul></ul><ul><ul><ul><li>Case/control studies </li></ul></ul></ul><ul><ul><ul><li>Cohort studies </li></ul></ul></ul><ul><ul><li>Experimental studies: investigator allocates exposure and follows development of disease </li></ul></ul>
  31. 40. Case/Control Studies <ul><li>Case/Control </li></ul><ul><ul><li>Compares those with disease to those without but with similar background and/or with prior exposure to certain risk factors </li></ul></ul><ul><ul><ul><li>Aimed at identifying factors more common in case than control group </li></ul></ul></ul>
  32. 41. Cohort Studies <ul><li>Cohort is classified by exposure to one or more risk factors and observed to determine rate of disease development </li></ul><ul><ul><li>Cohort: group of people who share important demographic characteristic </li></ul></ul><ul><li>Odds ratio </li></ul><ul><li>Relative risk </li></ul>
  33. 42. Experimental Studies <ul><li>Carried out to identify cause of disease or determine effectiveness of vaccine, drug, or procedure </li></ul><ul><ul><li>Control for variables </li></ul></ul><ul><ul><ul><li>Control groups </li></ul></ul></ul><ul><ul><ul><li>Randomization </li></ul></ul></ul><ul><ul><ul><li>Blinding </li></ul></ul></ul><ul><ul><li>Placebo: blank treatment </li></ul></ul>
  34. 43. Criteria of Causation <ul><li>Questions exposure causing development of disease </li></ul><ul><li>Criteria </li></ul><ul><ul><li>Strength </li></ul></ul><ul><ul><li>Consistency </li></ul></ul><ul><ul><li>Specificity </li></ul></ul><ul><ul><li>Temporality </li></ul></ul><ul><ul><li>Biological plausibility </li></ul></ul>
  35. 45. Discussion Questions <ul><li>How can data collection for notifiable diseases be improved? </li></ul><ul><li>Why is tracking vital statistics so important? </li></ul><ul><li>How does calculating Years of Potential Life Lost change the way we think about community health efforts? </li></ul>