Epidemiology 1 – Flashcards
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Public Health
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"Organized community efforts aimed at the prevention of disease and the promotion of health."
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Epidemiology
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"The study of the distribution and the determinants of health-related states and events in populations, and the application of this study to control health problems." -The study of health and disease in the populations. -Promote, protect and restore health
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Study
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Measurement of disease frequency, involving the QUANTIFICATION of the existence or occurrence of disease
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Distribution
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Frequency of disease by person, place, and time.
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Determinants
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Any factor or event that brings about a change in a health condition
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Exposure
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Agents, intervention, conditions, policies, or anything that might affect health. -Refers to determinants
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Disease
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Commonly used to refer to all health-related states or events
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Morbidity
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Refers to illness
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Mortality
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refers to death
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The scope of Epi
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-Describe the health status of populations -Explain the etiology of disease -Predict the occurrence of disease -Control the distribution of disease
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Epidemic
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Unusual or increased frequency of an adverse effect in the population.
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Hippocrates
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-First Epidemiologist -Used the terms "epidemic" and "endemic" -"On Airs, Waters, and Places" -Believed disease was due to imbalance in 4 bodily humors. (Black and yellow bile, phlegm, blood) -Associated disease with place, water conditions, eating habits, and housing.
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James Lind
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-Experiments with Scurvy (vit. C deficiency) -Experiment: 12 sailors w/classic signs/symptoms. Divided into groups of 2. Gave different diets to groups. Men on citrus diet fit for duty 2-6 days. -Made clinical observations, experimental design, observed population changes, considered source of disease
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Edward Jenner
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-Observed milkmaids got cowpox but not small pox. -Invented a vaccine for smallpox
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Ignaz Semmelweis
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-Childbed Fever -Very high mortality rates for mothers giving birth. (25%) -Many believed was caused by bad air -Difference in mortality rates between physicians and midwives. -Implemented hand-washing intervention
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Joseph Goldberger
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-Non-infectious origin of Pellagra (Vit. B deficiency) -Noticed inmates contracted disease and not staff -Suspected diet was issue -Experiment: 11 volunteer prisoners given corn based diet only. 6/11 developed pellagra after 5 months. -Niacin was discovered after his death -Non-infectious disease epi -Prevention and control disease before cause identified.
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John Snow
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-Father of Epi -Cholera -Used spot map to see the distribution of disease. -Hypothesized disease was spread in water supply -Identified water as the vehicle -Removed pump handle
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Framingham Heart Study
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-Looked at cholesterol and heart disease in a community. -First prospective cohort study
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Two Fundamental Assumptions
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-Disease does not occur at random -Human disease has causal and preventive factors. (Essence of Epi=comparison)
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Epidemiologic Triangle
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-Host:Biological and social Traits -Agent: Bacteria, virus, alcohol, trauma... -Environmental: Climate, pollution, economic, social
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3 Major Contributors
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-Basic Science: Biochemistry, physiology, pathology... -Clinical: Clinical medicine, urology, oncology, gynecology... -Population Medicine: Public health, epi, social medicine...
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Clinical Medicine vs. Epi
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Clinical: -Examines disease among individual -Describes signs and symptoms Prescribes individual treatment Epi: -Examines disease among populations -Describes age groups, time trends, geographic trends, etc. -Prescribes interventions for the community and evaluates
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Research Strategies (Study Designs)
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-Experimental: Clinical trials, Field Trails -Observational: ~Descriptive-Patterns of disease by person, place, and time ~Analytic-Testing hypothesis
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Epidemiologic Transition
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-Changes from infectious disease to chronic
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Count
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-# of cases of a health event
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Ratio
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-Division of one quantity by another
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Proportion
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- a ratio in which the numerator is contained in the denominator -Tells us what fraction of the population is affected.
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Rate
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-A ratio representing change over TIME
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Odds
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-Probability of an event (P) divided by the probability of a non-event (1-P)
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Calculating measures of disease frequency
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# of events in a specified period/population at risk of the event during the specified time * K
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Prevalence Proportion
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-The proportion of the population who have the disease at a given time. # of existing cases of a disease at a given point in time/total population *1000
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Point Prevalence
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# of existing cases of a disease at a point in time/ total population at the same time *1000
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Period Prevalence
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# of existing cases of a disease during a period of time/ Average population during the same period of time *1000
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Criteria needed to calculate prevalence
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-Health status of population -specification of numerator (New and old cases) -size of population -point or period of observation
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Cumulative Incidence (Risk)
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-Proportion of initially susceptible individuals in a population who develop new cases of a disease in specified time. # of new cases/population at risk *1000
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Incidence Rate (density)
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# of new cases/total person time at risk *1000
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Person-time
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-Estimate of the actual time at risk that all persons contribute to the study. -Person eligible as long as they are susceptible.
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Uses of Prevalence
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-Not a measure of risk -Used to express burden of disease -used by health planners to determine work load
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Uses of Incidence
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-Tells about change in status from non-diseased to diseased. -Direct indicator of risk Comparing rate in populations
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Interrelationship between incidence and prevalence
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-Prevalence depends on ~Incidence ~Duration of disease P = I*D
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Mortality Rate
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-Incidence of death in a population
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Examples of Mortality Rates
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-Crude Mortality: # of deaths/total population for year -Cause-Specific Mortality: # of deaths from specific cause/ total population for year -Age-Specific mortality: #of deaths for age group/total population in age group
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Artifactual Reasons for changes in Mortality
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-Error in numerator due to: ~recognition of disease ~rules and procedures for classification of causes of death ~accuracy of reporting age at death -Error in the denominator due to enumeration of the population
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Real Reasons for changes in Mortality
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-Changes in age distribution of population -survivor-ship due to treatment -changes in incidence of disease resulting from genetic factors or prevention
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Proportionate Mortality Ratio (PMR)
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-Useful for identifying leading cause of death # of deaths from given cause in a specified period of time/total deaths in the same period of time per 100
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Case Fatality
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-Refers to the fatal cases among those who have the disease #of deaths due to disease X/# of cases of disease X *100
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Infant Mortality Rate
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-Shows unmet health needs -unfavorable environmental factors # of deaths among infants < 1 year in a specified time/# of live births in that same time * 1000
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Maternal Mortality Rate
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-Considered to reflect adequacy of obstetric care and general level of S.E. Development # of deaths related to childbirth/ # of live births *100,000
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Other "Rates"
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Attack Rate: # of new cases/those exposed Crude Birth Rate: # of live births per average population Fertility Rate: live births per population of women of child-bearing age
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Descriptive Epi
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-The study of the distribution of disease in population groups -Person, place and time
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Person
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-Age -Gender -Race/Ethnic Group -Social Class -Occupation -Marital Status -Family Variables
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Place
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-Natural Boundaries (Climate,temperature, water supply) -Political Subdivisions -Urban-rural -International -Migrant Studies
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Time
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-Secular Trends (years/decades) -Cyclic or Seasonal Changes (annual, monthly, weekly) -Short-term fluctuation -Time/place clusters
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Active Surveillance
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-Reports are solicited from reporting sources at established intervals. -Burden of reporting on you.
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Strengths/Limitations to active reporting
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Strengths: -Rapid -Increased sensitivity/specificity -May increase collection of appropriate specimen. Limitations: -Resource intensive -difficult to maintain for extended periods of time
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Passive Surveillance
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-Reporting sources send in reports of disease at will. -Burden of disease on those who are reporting.
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Strengths/Limitations to Passive Surveillance
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Strengths: -Simple -Not overly burdensome in the PH system Limitations: -Completeness of reporting -Under-reporting is likely.
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Sentinel Surveillance
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-Key reporting sources are selected to participate in an enhanced disease surveillance
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Strengths/Limitations to Sentinel Surveillance
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Strengths: -Valid and reliable -Rapid -Good for temporal tendencies Limitations: -Who does it represent? -Labor intensive -Difficult to be used for prevalence estimates
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Syndromic Surveillance
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- A group of symptoms that collectively indicate or characterize a disease, psychological disorder, or abnormality. -Potential for identifying Bio-terror Events
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Strengths/Limitations to Syndromic Surveillance
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Strengths: -May provide early recognition of an ID outbreak or BT event -Assures ongoing, systematic surveillance once set up Limitations: -Numerous software packages -require compatible electronic formats -Difficult to define sensitivity to individual
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Data Source Consideration: Outcome under study?
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-Mortality -Morbidity -Risk Factors
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Data Source Consideration: Population under study?
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-National -State -Specific Group
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Data Source Consideration: Purpose of the Study?
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-Assessment of community needs -Health planning -Program evaluation -Research
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Issues in use of Secondary Data
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Strengths: -Already collected (Save money) -Often very large numbers readily available Limitations: -Original purpose for collecting data -completeness -confidentiality issues -timeliness of data available VERIFY data quality
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Types of Data used in PH and Epi studies
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-Demographic (Census-Main source) -vital stats -health status and behavioral data -surveillance data -socioeconomic data
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Graphs
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Graphs: -For the forest (entire group) -Show pattern, shapes, and trends -Fit more info in small space Pie Charts Bar Charts Line graphs Histogram
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Tables
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-For the trees -Show exact values Needs: -clear and simple summary -Title clear and concise -Rows and columns clearly labeled -No unnecessary digits -Lines to separate items Title: -Descriptive of the data -time frame for the data -place -sample size
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Common Errors
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-Use the wrong kind of graph -Failure to illustrate that a graph begins somewhere other than zero -Inappropriate scale -Inadequate titles or labels No sample size reported
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3 Categories of Measures
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-Crude: Summary measures for total population. -Specific: Measures for population subgroups and restricts the numerator and denominator to specific group - Adjusted:Total population statistically transformed to remove the effect of differences in the population composition. ~Allows fair comparison
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Why Standardize?
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-To compensate for differential age distributions
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Direct Standardization
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-Uses age distribution of external reference population. -Needed info: ~# in each age group for the reference populations to be compared ~Observed # of deaths for each age group ~# in each age group for the standard population
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Direct Standardization Procedure
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-Calculate age-specific rate for each population to be compared. -multiply age-specific rate time the standard pop for each age group -this should give you the expected # of deaths -total expected # of deaths for all age groups -divide expected total by the total standard population
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Indirect Standardization
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-Used when age -specific rates are unavailable in the study population -Computes the standardized mortality/mortality ratios (SMR) -Comparison of observed to expected -Needed info: ~# in each age-group for the populations to be compared ~total # of deaths in the populations to be compared. ~Age-specific death rates for the selected standard pop.
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Indirect Procedure
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-Multiply standard pop age-specific death rates by # in each age group of populations to be compared. -This will give you the expected # of deaths -Sum the expected # of deaths Calculate SMR=Observed/expected
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Advantages/ Disadvantages: Frequency
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Advantages: -Actual number of events -useful for determining need for services or programs Disadvantages: -Influenced by size of population
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Advantages/ Disadvantages: Crude Rates
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Advantages: -Summary rate -Easily Calculated Risk of dying in the population for a given time Disadvantages: -Influenced by population characteristics -Comparisons may be confounded by these characteristics
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Advantages/ Disadvantages: Specific Rate
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Advantages: -Calculated for homogeneous subgroups -Comparisons of different populations -Identifies subgroups at risk Disadvantages: Cumbersome to compare more than two subgroups of two or more populations of interest.
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Advantages/ Disadvantages: Adjusted Rates
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Advantages: -Differences in the adjusted factor between populations is removed -Permits unbiased comparison relative to adjusted factor Disadvantages: -Artificial rates -Does not represent the risk of dying -absolute magnitude dependent on standard population chosen.
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Plague: Black Death
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-Manifestation: Bubonic, pneumonic,septicemic -Transmission: Flea to person, person to person, animal to person -30-50% of pop. died
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Anton van Leeuwenhoek
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-Refined the microscope -Documented observations
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Louis Pasteur
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-Developed pasteurization method -Ruled out theory of spontaneous generation -Developed rabies vaccine
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Robert Koch
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-Formulated postulates: 1.Microorganisms must be in in organisms suffering from disease 2.Microorganism must be isolated from diseased organism and grown in pure culture 3.Cultured microorganism should cause disease when introduced into healthy organism 4.Microorganism must be re-isolated from inoculated, diseased host and identified as being identical to original causative agent.
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Watson and Crick
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-Demonstrated the double helix nature of DNA
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Features Specific to Infectious Disease
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-Infected people become exposures to others -Host can be immune -Infectiousness typically temporary -Infected people may be asymptomatic for various periods of time. -Diseased people may or may not be infectious to others -Time frame may be urgent
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Infected
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-Foreign agent that multiplies within the host and body reacts to presence. ~Asymptomatic ~Symptomatic ~Latent infection
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Colonized/Carrier
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-Persistence and multiplication of agent on mucosal surface w/o apparent host reaction.
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Contamination
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-Presence of agent on surface of body or inanimate object may serve as source of infection
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Time Lines for Infection and disease
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Dynamics of infectiousness: -Susceptible -Latent -Infectious -non-infectious(Removed, dead, recover) Dynamics of disease: -Susceptible -Incubation Period -Symptomatic Period -Non-diseased (Dead. recovered, immune, carrier)
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Herd Immunity
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-Enough people in a population are immune such that it does not spread to susceptible people
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Outbreak
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-An epidemic limited to localized increase in the incidence of a disease or health-related event. -Two or more cases from different households of potentially infectious disease of unknown etiology
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Case Control
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-More commonly used -Population at risk is not known
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Cohort
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-When you have a defined group
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Challenges of Investigation
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-Small sample size -Irregular and dynamic data sources -Hampered collection environmental specimens. (Arrive after the fact) -Bias created by media -Reluctance from participating -Conflicting of timing for intervention
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Steps to and Outbreak investigation
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1. Establish Existence of Outbreak: Collect specific information from source. (Who, When, What) 2. Confirm the diagnosis: Determine if the clinical specimens have been obtained 3. Define a case and count Cases: Create case definition(Lab testing, symptoms, time) Must be workable. -Create a line list 4. Orient data to time, place, person: -Time: Epidemic Curve: person to person or pinto source -Place: Plot the data on a map (disease may be associate with location) -Person: Examine characteristics: Age, gender, race, occupation 5. Determine who is at risk for becoming ill: Community wide, Restaurant attendees, etc. 6. Develop a hypothesis and test: 7. Compare hypothesis with established scientific knowledge 8. Plan a more systematic Study 9. Communicate findings 10. Execute control and prevention measures
