Epidemiology

Front 1

What are the two things that define epidemiology?

Back 1

Distribution and Determinates

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descriptive epidemiology

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distribution

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analytic epidemiology

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determinants

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deals with individuals isolated from their environment

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clinical medicine

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deals with populations of people in their natural environments

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epidemiology

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why does epidemiology exist?

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because disease is not randomly distributed

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Father of modern medicine, described the relationship between health and the environment

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Hippocrates

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founder of vital statistics, first to use quantitative methods

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John Graunt

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studied the cholera outbreaks in london, studied the relationship between water supply and disease cases, demonstrated the mode of cholera transmission before causative agent identified.

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John Snow

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devised standard nomenclature and classification system (ICD).

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William Farr

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The London Cholera Epidemics was an example of

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a natural experiment

Front 12

What are the two measures that are important steps in the investigation of an outbreak?

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1. Take immediate control measures
2. Report Findings

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organizing and summarizing information in a clear and effective way, includes construction of graphs, charts, ect., includes calculation of averages and percentiles

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descriptive statistics

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election results and sports statistics are examples

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descriptive statistics

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use a sample to make inferences about a populations

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inferential statistics

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political polling is an example

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inferential statistics

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polio vaccine study was an example

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inferential statistics

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quantitative indices that describe the center of distribution

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mean, median, mode

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the most commonly used measure of central tendency

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mean

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the number that divides the bottom 50% of the data from the top 50%

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median

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middle number in an ordered data set

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median

Front 22

used in data sets with high variability

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median

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the data value, or values that occur most frequently in a data set

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mode

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if the data is normally distributed what do you use?

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mean

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influenced by all observed values and is sensitive to outliers

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mean

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depends only on values in the middle of the data set and is robust

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median

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ignores all values except the ones with the highest frequency

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mode

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measures the variation in a data set by determining how far the data values are from the mean, on average

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standard deviation

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what percent of the population is within one standard deviation

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68%

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what percent of the population is within two standard deviations

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95%

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what percent of the population is within three standard deviations

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99%

Front 32

used with normal distribution
z and t tests

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parametric studies

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used when you are not sure the population is normally distributed
chi squared independence test

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nonparametric statistics

Front 34

what is the first stage of the natural history of disease?

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Stage of susceptibility

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what is the second stage of the natural history of disease?

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Stage of presymptomatic disease

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what is the third stage of the natural history of disease?

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Stage of clinical disease

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what is the fourth stage of the natural history of disease?

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Stage of disability/ recovery

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no disease but presence of factors that favor its occurence (risk factors)

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Stage of susceptibility

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no manifest disease, but pathogenic stages have started to occur, changes are below the level of the clinical horizon

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Stage of presymptomatic disease

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there are recognizable signs or symtpoms of the disease, crossed the clinical horizon

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Stage of clinical disease

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some diseases result in residual defect of short or long duration that leave the person disabled to a greater or lesser extent

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Stage of disability/ recovery

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stage of susceptibility
general health promotion
specific protective measurements

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Primary Prevention

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immunization, sanitization, protection against injury, eye protection are examples

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Primary Prevention

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early stages (preclinical and early clinical stages)
early detection and prompt treatment
attempt to cure disease or slow its progression

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Secondary Prevention

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Advanced disease or stage of disability
limitation of disability and rehabilitation

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Tertiary Prevention

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constant presence of disease within a given geofraphic area. the usual presence of the disease

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endemic

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the occurrence of a disease in excess of normal expectancy within a geographic area. no specific time, area, or number of cases

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epidemic

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disease cannot be attributed to the operation of any one factor
more that one factor must be present for disease to occur

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multiple causation of disease

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a state of altered responsiveness to a specific substance through immunization or natural infection

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specific immunity

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factors in population dynamics

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births
deaths
migrations

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Vital statistics

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Birth rates
Death rates

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reportable diseases

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patients are identified to prevent multiple reports, not anonymous until state reports to CDC

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number of years an individual is expected to live,
generally used to refer to life expectancy at birth, can be calculated at any age

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life expectancy

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what is the greatest adavances in US with life expectancy

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increasing survival in infancy and early childhood

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the number of new cases of disease in a population over a period of time

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incidence

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the probability that a non-diseased individual will develop a specific disease during a specified period of time

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incidence

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number of new cases/ population at risk

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incident rate

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the number of individuals who have a particular disease at a given time

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prevalence

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number of existing cases/ population at risk

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prevalence

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What are the leading causes of death in the US (all ages)?

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1. Heart disease
2. Cancer
3. Stroke

Front 61

determine the amount and distribution of a disease within a population by person, place, time

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descriptive studies

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focus study of the determinants of a disease or reasons for high or low frequency in specific group

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analytic studies

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identifies non-random variations in the distribution of disease to enable an investigator to generate testable hypothesis regarding etiology

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descriptive studies

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reveals the patterns of disease occurrence in human populations

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descriptive studies

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age, gender, ethnicity, socio-economic status, marital status

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descriptive studies

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marital status from lowest to highest vs. morbitiy/mortality rate

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married, single, widowed, divorced

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diseases that depend on specific environmental conditions

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place diseases

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malignant melanoma, MS

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place diseases

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once descriptive studies have identified groups with high or low rates of disease, analytic studies are performed to determine why the rate is high or low

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analytic studies

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used to determine disease rates

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analytic studies

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identification of risk factors

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analytic studies

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case control study
compares cases and controls, controls do not have the disease, look at past exposures for possible risk factors

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retrospective study

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usually performed before prospective, less expensive, faster, depends on reliable medical records and patient recall

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retrospective study

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never provides incidence rates

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retrospective study

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cohort study, all subjects are disease free at the start of the study, subjects divided into groups based on exposure to suspected risk factor, follow subjects to see who develops the disease

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prospective study

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loner, more expensive

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prospective study

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provides incidence rates

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prospective study

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ratio of incidence rates of those exposed to those not exposed

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relative risk

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estimate of relative risk

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odds ratio

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relative risk > 1.0

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risk factor

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relative risk = 1.0

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no risk

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relative risk < 1.0

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protective

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determined by measurements of :
sensitivity
specificity

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validity

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the ability of a test to identify correctly those who have the disease

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sensitivity

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true positives/ all who have the disease

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sensitivity

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the ability of a test to identigy correctly those who do not have the disease

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specificity

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true negatives/ all without the disease

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specificity

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the ability of a screening test to predict the presence or absence of a disease depends on:
the prevalence of disease
the sensitivity and specificity of the screening test

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predictive value

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true positives/ all positives

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predictive value

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the higher the prevalence, the more likely it is that a positive test is predictive of the disease

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predictive value

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precision or repeatability

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reliability

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the amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of the screening

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yield

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sensitivity of the test, prevalence of unrecognized disease, multiphasic screening, frequency of screening, participation in screening and follow up

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factors affecting yield

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the ability of an agent to invade and multiply in a host

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infectivity

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the ability of an agent to produce infection

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infectivity

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the ability to produce clinically apparent illness

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pathogenicity

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the percentage of infections that result in illness

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pathogenicity

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the proportion of clinical cases resulting in severe clinical manifestations

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virulence

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Case fatality rate is one measure

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virulence

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the infections ability to produce specific immunity

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immunogenicity

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resistance of a group to invasion and spread of an infectious agent based on immunity of a significant portion of the group

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herd immunity

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5% of infected have active disease within one year and another 5% wikk have active disease in a lifetime

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TB

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aggregation of cases over a period of time in a place

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cluster

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a cluster that is unexpected, synonymous with epidemic

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outbreak

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Legionnaires disease specifics

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july, cases 221, CFR 15%, CDC involved because an epidemic of swine flu had been predicted, inhaled, resulted in A/C standards changed to require more stringent cleaning and hygiene of large scale A/C systems

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Hanta Virus specifics

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American Southwest, May, cases 19, CFR 63%, dear mice, inhaled, respiratory illness

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Attack rate

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% ill who ate each food item
% ill who did not eat each food item

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refractive errors are normally distributed

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only at birth

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early infancy

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most are emmetropic or slightly hyperopic

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myopia increases in childhood each year

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until 25% at age 18

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adulthood

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increase in hyperopic prescriptions with aging,
some increase in myopia due to cataract

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prevalence of vision disorders at age 5

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15%

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prevalence of vision disorders at age 20

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30%

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prevalence of vision disorders at age 40

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40%

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prevalence of vision disorders at age 45

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100%

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incidence rate of vision disorders is

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1.6% per year from age 5-15

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eye disease increases with

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age

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eye disease affects about what percent of the us population

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5%

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the incidence of eye disease is about what percent per year?

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1%

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what are the three leading causes of blindness in the US

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1. Cataracts
2. Glaucoma
3. ARMD

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leading causes of blindness worldwide

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1. Cataract
2. degenerative and metabolic disease
3. trachoma
4. glaucoma
5. onchocerciasis and vitamin A deficiency

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prevalence of POAG

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2% over age 40

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incidence of POAG

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has not been accurately measured

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POAG accounts for what percent of adult glaucoma

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70%

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risk factors for glaucoma

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age, race/ethnicity, family history, increased IOP, increased C/D ratio, asymmetric cupping, NFL loss, myopia, diabetes, systemic hypertension

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Is there a good screening test for glaucoma?

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NO

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Gather and report data, no hypothesis gathered

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descriptive studies

Front 128

designed to test a hypothesis, study design should be appropriate to test the hypothesis

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explanatory study

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observational,
experimental

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explanatory study

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researcher does not manipulate variables, used to evaluate the course of the disease or the relationship between risk factors and outcome, address questions about prevalence, natural history, or etiology

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observational

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used to evaluate preventive or therapeutic interventions and provide more substantial evidence of causality

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experimental

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ecological studies, cross sectional studies, case control studies, cohort studies

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observational

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observational study conducted at the population level rather than the individual level

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ecological studies

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difference in outcome between populations are related to population characteristics that are risk or protective factors

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ecological studies

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also called prevalence studies, select a sample of subjects and determine the distribution of exposure in the sample, exposure and disease outcome are determined simultaneoulsy, can not be used to determine temporal relationship between exposure and disease

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cross sectional studies

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retrospective, case, conrol, if exposed to a risk factor, the proportion of cases should be greater than the controls exposed, recall bias can be a problem since past events are involved

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case control studies

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participants are all disease free at the start of the study, divide participants according to exposure and folow over time to look for development of disease, expensive, attrition and selection bias are other issues to consider, prospective

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cohort studies

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clinical trials, community trials

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experimental studies

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experimental study where researcher controls exposure, gold standard is double masked clinical trial

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clinical trials

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risk factor or exposure under investigation, study may involve multiple risk factors under investigation, look at measurement/ classification of exposure

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predictor variable

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must look at analysis used to exclude chance as an explanation for findings (5%)

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statistical analysis

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subjects in the study have characterisitics that preferentially lead to a particular outcome

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selection bias

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avoid by choosing subjects randomly

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selection bias

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arises from systematic errors in measuring either the independent variable or the dependent variable, systematic error in measurement or limited precision in measurement

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information bias

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extraneous correlate of disease that, because of its association with the risk factor of interest, accounts for some or all of the observed association

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confounder

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one that is associated with exposure and is an independent risk factor for disease

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confounding variable

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eliminate or reduce with careful study design and participant selection

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confounding

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participants of Orinda Study

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suburban population

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major goal or orinda study

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to design the least expensive, least technical, and most effective screening program for finding essentially all elementary school children with vision problems

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results: ranked by efficiency for orinda study

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1. MCT
2. California procedure
3. Mass Vision kit
4. Parent questionaire
5. nurse observation
6. teacher observation

Front 151

which is most likey to cause a referal according to the orinda study?

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refractive error

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which is the least likely to cause a referal according to the orinda study?

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disease

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participants of the Framingham eye study

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largely white, middle class, suburban

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purpose of Framingham eye study

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to determine the epidemiology of ocular pathology in the study group

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results of the Framingham eye study

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visual impairment increases with age,
C/D ratio mean= 0.28 (sd=0.17)

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participants of the Baltimore eye study

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urban, multiracial population

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Purpose of the Baltimore eye study

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to determine blindness and visula impairment rates among an urban, multiracial population

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results of the Baltimore eye study

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blindness and visual impairment increased with age in both groups but age adjusted rates were twice as high for blacks thank for whites

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studying groups of people to gather evidence to help make clinical decisions in patient care. studying variations in the outcome of illness and the reasons for the variation.

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clinical epidemiology

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changing the odds based on the info that you have and that you gather

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conditional probability

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what are the initial odds for conditional probability?

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prevalence, incidence, risk factors

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what are the new odds for conditional probability?

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sensitivity, + predictive value

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the integration of current best evidence with clinical expertise, pathophysiological knowlede, and patient preferences to make health care decisions

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evidence based medicine

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evidence based medicine involves:

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1. clinical experience
2. knowledge of pathophysiology
3. patient preference
4. outcomes of latest clinical research

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what must the physician be familiar with to practice evidence-based medicine?

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the latest research

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treating ocular hypertension can delay or prevent the onset of POAG

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Ocular Hypertension Treatment Study

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found that high levels of antioxidants and zinc can reduce the risk of developing ARMD

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Age Related Eye Disease Study

Front 168

found that Atropine therapy works as well as traditional patching therapy for the treatment of amblyiopia

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Amblyopia Treatment Study

Front 169

Aspirin has no effect on progression of retinopathy, focal treatment for macular edema reduced vision loss, small reduction in severe vision loss using scatter treatment in NIDDM

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Early Treatment Diabetic Retinopathy Study