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Ch03 outline
- 1. Epidemiology: The Study of Disease, Injury, and Death in the Community Chapter 3
- 2. Introduction • Epidemiology =population medicine • Epidemiologists concerned with course of disease in a population • Collect information about disease status of a community • How many people are sick? Who is sick? When did they become sick? Where do they live? • Data can be used to prevent disease outbreaks or determine effectiveness of prevention effort
- 3. Definitions • Epidemiology: studyof distribution and determinants of health-related states or events in specified populations • Epidemic: unexpectedly large number of cases of an illness, specific health-related behavior or event, in a particular population • Endemic: disease that occurs regularly in a population as a matter of course • Pandemic: outbreak over wide geographic area
- 4. The Importance ofRates • Rates allow for comparison of outbreaks at different times or in different places • Cases: people afflicted (those who are sick) • Rates: number of events in a given population over a given period of time or given point in time • Natality (birth), morbidity (sickness), mortality or fatality (death) rates • Population at Risk: those susceptible to particular disease or condition
- 5. Morbidity Rates • Incidencerate: 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 • Prevalence rate: number of new and old cases in a given period of time, divided by total # in that population • Attack rate: incidence rate calculated for a particular population for a single disease outbreak; expressed as a percentage
- 6. Incidence, Prevalence, andAttack Rates • Incidence rates important to study of acute diseases • Acute disease: lasts three months or less • Prevalence rates useful for study of chronic diseases • Chronic disease: last longer than three months • Incidence and prevalence rates expressed as crude or specific
- 7. Incidence, Prevalence, andAttack Rates
- 8. Crude and Age-AdjustedRates • Crude rates: denominator includes the total population • Crude birth rate: # of live births in given year, divided by midyear population • Crude death rate: # of deaths in given year from all causes, divided by midyear population • Age-adjusted rates: used to make comparisons of relative risks across groups and over time when groups differ in age structure
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- 11. Specific Rates • Measuremorbidity and mortality for particular populations or diseases • Case fatality rate: percentage of cases of a particular disease that result in death • Proportionate mortality ratio: percentage of overall mortality in a population that is attributable to a particular cause
- 12. Important Rates inEpidemiology
- 13. Reporting of Birth,Deaths, and Diseases • Physicians, clinics, and hospitals required to report births, deaths, and notifiable diseases • Notifiable diseases: infectious diseases in which health officials request or require reporting • Can become epidemics • Health officials maintain weekly records • Various challenges to maintaining accurate data
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- 15. Standardized Measurements ofHealth Status of Populations • Mortality statistics most reliable measure of population health status • Easier to track death than illness • Life expectancy: average number of years a person from a specific cohort is projected to live from a given point in time • Years of potential life lost (YPLL): number of years lost when death occurs before one’s life expectancy
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- 17. Years of PotentialLife Lost • Subtract person’s age at death from his or her life expectancy • Difficult to determine because life expectancy changes at different ages • Weighs death of young person as counting more than death of old
- 18. Sources of StandardizedData • Various valid sources have specific value and usefulness to those in public health • U.S. Census • Taken every 10 years • Enumeration of the population • More complex now • Gathers data on race, age, income, employment, education, and other social indicators
- 19. Sources of StandardizedData (ctd) • Statistical Abstract of the United States • Book published annually by Bureau of Census • Summary of statistics on social, political, and economic organization of the United States • Monthly Vital Statistics Report • Vital statistics are summaries of records of major life events: birth, death, marriage, divorce • Published by National Center for Health Statistics under the CDC • Also calculates death rates by race and age
- 20. Sources of StandardizedData (ctd) • Morbidity and Mortality Weekly Report (MMWR) • Prepared by CDC from state health department reports • Reports morbidity and mortality data by state and region of U.S. • Reports outbreaks of disease, environmental hazards, unusual cases, or other public health problems
- 21. National Health Surveys •National Health Survey Act of 1956 authorized continuing survey of amount, distribution, and effects of illness and disability in the U.S. • Three types of surveys • Health interviews of people • Clinical tests, measurements, and physical examinations • Surveys of places where people receive medical care
- 22. Some National HealthSurveys • National Health Interview Survey (NHIS) • Conducted by NCHS • Questions respondents about their health • National Health and Nutrition Examination Survey (NHANES) • Assesses health and nutrition status through mobile examination center • Behavioral Risk Factor Surveillance System (BRFSS); National Health Care Survey (NHCS)
- 23. Epidemiological Studies • Investigationscarried out when disease or death occurs in unexpected or unacceptable numbers • Descriptive studies • Describe epidemics with respect to person, place, and time • Analytic studies • Aimed at testing hypotheses
- 24. Descriptive Studies • Who? • Case count, followed by who is ill (children, men, women, race, etc.) • When? • Time of onset for each case • Epidemic curves created • Where? • Determine residential address and travel history
- 25. Epidemic Curves • Graphicdisplay of the cases of disease according to the time or date of onset of symptoms • Secular, seasonal, and single epidemic curves • Single epidemic curves • Point source epidemic curve • Propagated epidemic curve
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- 30. Analytic Studies • Testhypotheses about relationships between health problems and possible risk factors • Observational studies: investigator observes natural course of events, noting exposed vs. unexposed and disease development • Case/control studies • Cohort studies • Experimental studies: investigator allocates exposure and follows development of disease
- 31. Case/Control Studies • Case/Control • Compares those with disease to those without but with similar background and/or with prior exposure to certain risk factors • Aimed at identifying factors more common in case than control group
- 32. Cohort Studies • Cohortis classified by exposure to one or more risk factors and observed to determine rate of disease development • Cohort: group of people who share important demographic characteristic • Odds ratio • Relative risk
- 33. Experimental Studies • Carriedout to identify cause of disease or determine effectiveness of vaccine, drug, or procedure • Control for variables • Control groups • Randomization • Blinding • Placebo: blank treatment
- 34. Criteria of Causation •Questions exposure causing development of disease • Criteria • Strength • Consistency • Specificity • Temporality • Biological plausibility
- 35. Discussion Questions • Howcan data collection for notifiable diseases be improved? • Why is tracking vital statistics so important? • How does calculating Years of Potential Life Lost change the way we think about community health efforts?