# epi

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1. Epidemiology:
• study of distribution and determinants of health related states or events in specific populations and the application of this study to control health problems
• • Goal, essentially, is to limit undesirable health events in a community

• Epidemic:
• an unexpectedly large number of cases of an illness, specific health-related behavior, or other health related event in a particular population at a particular time and place

• Endemic disease:
• disease that occurs regularly in a population

• Epidemiologist
• : studies disease occurrence in defined populations

• Pandemic: outbreak of a disease over a wide geographical area, such as a continent
• • Example: avian influenza, which the books list as being the next possible agent to reach pandemic proportions.

• History of Epidemiology: 300 B.C., late 1600’s, 1849:
• : Hippocrates suggests link between disease and environment
• •1849: John Snow studies epidemiology of cholera and extinguishes London outbreak, thereby limiting death and preserving health
2. •Natality:
births / total population
3. •Morbidity:
number of sick / total population at risk
4. •Mortality:
• number deaths / total population at risk
• Based on population risk: those who are susceptible to a disease in a given population
5. Incidence rate:
number of new health related cases of a disease / total number in population at risk
6. The Importance of Rates Prime importance:
• •Number of events
• •Number of cases: the number of people who are sick
• •Number of deaths
7. •Acute disease:
lasts less than 3 months
8. •Chronic disease:
lasts longer than 3 months
9. •Attack rate:
• incidence rate calculated for a specific population for a single disease outbreak expressed as a percentage
• oEx: number of people on a flight become sick, and it is suspected that the flight caused the illness. Attack rate could be calculated for the passengers to express who became ill.
10. •Prevalence rates:
• all current cases / total population
• oUseful for chronic diseases: know how many are suffering
11. •Crude rate:
denominator includes total population
12. oCrude birthrate:
• # births in a year / mid year population
• +: easy to obtain, good for comparing populations
• -: misleading if populations differ in age/attributes
rate used to make comparisons between groups over time when groups differ in age structures
14. •Specific rates:
measures morbidity or mortality for particular populations or diseases
15. Cause specific mortality rate (CSMR):
• death rate due to a particular disease
• Number of deaths by disease / total population
16. Case fatality rate (CFR):
• percentage of cases of a disease that result in death
• # deaths in specified time / number of cases in same period
17. Proportionate mortality ratio (PMR):
• percentage of overall mortality in a population that is attributable to particular cause
• # deaths due to specific disease / total number of deaths from all causes in same population in the same period of time
18. notifiable diseases problems
• • sometimes only 35% of cases with diseases are reported
• • clinics may be too busy to report every case
• • patients can recover before treatment and may not seek care
• • reporting depends on disease severity
19. most reliable indicator of a population health’s status
mortality statistics
20. • Age adjusted rates show ...
• what death would be if no changes occurred in the age makeup of a population
• o they are a better indicator for examining changes in risk of death over a period of time
21. -Life expectancy:
• average number of years a person from a specific cohort is projected to live from a given point of time
• • has generally increased in America

• -Years of potential life lost (YPLL):
• subtracting a person’s age at death from a predefined, standard age
• •age 75 often used as the standard
• operson dies at 59. 75-59 = 16 years
• vary depending on cause
• Accidents, cancer kill younger so higher YPLL

• measure for the burden of disease that takes into account premature death and loss of healthy life resulting from disability
• •mortality does not express burden of disease
• Ex: polio causes loss of healthy life but not reflected in death tables
sometimes referred to has healthy life expectancy, number of years of healthy life expected, on average, in a given population
23. -US Census: taken every 10 years; enumeration of the population living in the US
• •data: income, employment, family size, education, dwelling type, and many other social indicators
• •used for calculating disease and death rates for program planning
24. Vital statistics:
• statistical summaries of vital records; records major life events
• •births, deaths, marriages, divorces
• birth: maternal and prenatal care, delivery
• deaths: rates, expectancy, leading causes, infant mortality

• Morbidity and Mortality Weekly Report
• -reported diseases are shown weekly
25. -National Health Surveys:
• •health interviews of people
• •clinical tests
• •survey of places where care is received
26. -NHANES: National health and nutrition examination survey
• •health/nutritional of the general US Population
• •based on PE, clinical and lab tests, and related procedures
• o most authoritative source of clinical info on American people
27. -Behavioral Risk Factor Surveillance System:
state-based telephone survey to ascertain prevalence of high risk behavior, like smoking or drinking

• -Youth Risk Behavior Survey (YRBS): six categories of risks in youth
• •behaviors that contribute to unintentional violence and injuries
• •tobacco use
• •alcohol and drug use
• •STIS and pregnancy
• •HIV
• •Unhealthy dietary habits and physical inactivity

• -National Health Care Survey (NHCS):
• nine different national surveys that gather info on nation’s healthcare system
28. -Descriptive studies:
• describes disease with respect to person, place, and time (the extent, essentially)
• First studies carried out on diseases!! Valuable info on detection patterns.
• Who: head count, as well as age, sex, race, marital status, etc.
• When: categorized by time of occurrence
• Summarized by year, for example
29. Common source epidemic curve:
graphic display of disease where each case can be traced to a single source of exposure Used to calculate incubation period
30. incubation period:
time between exposure and onset of symptoms
31. Point source:
exposure occurs at a single point in time
32. Continuous source:
• exposure is intermittent
• Need to discover these to prevent future exposure
33. Propagated man parts: epidemic curve depicting distribution of cases traceable to multiple sources of exposure
• Primary cases appear at one end, secondary cases after primary, and tertiary further along the graph
• Where: residential addresses, travel history are recorded
• Restaurants, shopping, etc.
• •Limitations of descriptive studies: not applicable to outbreaks elsewhere and cannot provide info on disease trends.

• -Analytic studies:
• test hypotheses about relationships between health problems and possible risk factors
34. • Risk factors
• • increase probability of disease
• o Ex. Does smoking increase risk of lung cancer?
• • Two different types of analytic studies exist:
35. Observational studies:
• investigates natural course of disease
• Observational studies can be divided into:
36. Cross sectional:
info about exposure and disease are collected at the same time
37. Case/control:
• seeks to compare diagnosed with a disease and those who are not for prior exposure to specific risks
• • Don’t prove causation alone, but indicate future direction of question
38. o Cohort studies:
• cohort is classified by exposure to one or more risk factors and observed to determine the rates at which the disease develops in each class
• Can be prospective (observing a group to see if cigarette smoking leads to disease) or retrospectively (exposure and outcome has already happened)
39. o Case controls cannot calculate the
o rate of development of a disease, as the patients already have it
40. Odds ratio:
probability about association between risk factors and developing a disease
41. Cohort studies can
calculate incidence rate
42. Relative risk:
statement of relationship between risk factor and disease (more definitive)