Epidemiology Final: Part One – Flashcards
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epidemiology
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study of the distribution of disease and risk factors in the human population to determine disease etiology
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epidemiology examines
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distributions of incidence, mortality, risk factors, and related measures in time, place, and person
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time
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increase or decrease in disease over time?
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place
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do some geographic areas have different morbidity or mortality than other areas?
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person
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do the characteristics of persons with the disease distinguish them from those who are disease free?
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purpose of epidemiology
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elucidate etiology of disease, identify risk factors, quantify their importance, determine how, when and where to intervene
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Dr John Graunt
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analyzed mortality data and developed a better understanding of diseases as well as sources and causes of death
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Change in CVD mortality
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drastic decline (1950-2000)
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infant mortality
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decrease in infant mortality (African Americans have double compared to causasians)
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Top 2 causes of death in developing nations
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HIV/AIDS and lower respiratory infections
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epidemiologic transtition
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transition from infectious diseases as the predominant causes of morbidity and mortality to a predominance of chronic diseases during the 20th century
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strategies for disease prevention
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primary, secondary, tertiary prevention
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primary disease prevention
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eliminate exposure to the etiologic agent, altering susceptibility or reducing exposure for susceptible individuals
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active primary prevention of disease
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behavioral change (immunization, hand washing)
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passive primary prevention of disease
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no behavioral change (environmental sanitation, protection against injury)
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secondary prevention of disease
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screening for early detection of precursor conditions (benefit US; risk of screening depends upon cost, accuracy, and acceptance of the screening test in the population)
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tertiary prevention of disease
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limit disability from disease (rehabilitation, altering diet/exercise after cardiac event, compliance with medication schedule (glucose control in diabetes, blood pressure control in hypertension))
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Hippocrates
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father of medicine/epidemiology
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Edward Jenner
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discovered vaccine for smallpox, set stage for vaccinology
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Louis Pasteur
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invented germ theory of disease (1880)
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Willam Farr
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developed centralized registration system for disease classification (around 1870)
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Ronald Ross
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discovered that the vector of malaria was the mosquito
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John Snow
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cholera outbreak in London (1850), traced outbreak to broad street pump, took handle off, epidemic ceases
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Koch-Henle Postulates
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microorganism must be present in every case, must be isolated and grown in pure culture, inoculation of microorganism into susceptible host must reproduce disease, microorganism must be observed and recovered
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Paul Erlich
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development of anti-toxins (1890)
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Vaccinology in the 20th century:
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smallpox, polio, diptheria, measles, mumps, rubella, tetanus, influenza
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Joseph Goldberger
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looked at orphanages and institutions; discovered cause of pellagra is little vitamin B6 and niacin in diet (1913)
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Alexander Fleming
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discovered penicillin, couldn't isolate it from the mold (1928)
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Fred Sopher
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eradicated malarial mosquito (1939)
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Alice Hamilton
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founder of occupational medicine
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Janet Lane-Claypon
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first case control study of breast cancer risk factors of reproductive history
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stages in natural history of infectious disease
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susceptibility, exposure, incubation period, pathologic changes, symptoms, diagnosis and treatment, outcomes (recovery, disability, death) [clinical disease begins after symptoms]
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Components of infectious disease
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agents, reservoirs, portals of entry and exit, transmission, host immunity
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reservoir
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the natural habitat in which the microbe lives, multiplies, and grows (animals and inanimate objects)
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polio virus carriers
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paralysis (1%), nonparalytic disease (4%)
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hepatitis A carriers
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contagious (40% inapparent), jaundice (10% symptomatic)
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Typhoid Mary
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free of symptoms yet continued to harbor and shred the typhoid bacilli throughout her life
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prevalence of HIV
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prevalence still going up; 2.1 million deaths annually
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malaria transmission
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anopheles mosquito (kills over 1 million per year)
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plague transmission
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flea
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lyme disease transmission
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ticks
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typhus transmission
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louse
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west nile fever transmission
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tick or mosquito
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sandfly fever transmission
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sandfly
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chagas disease transmission
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African Tsetse fly
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river blindness
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transmitted by black fly, curable by Mectizan, microbe - filiarial worm
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immunization types
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active, passive, adoptive
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active immunization
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exposure to antigen induces specific antibodies (vaccines)
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passive immunization
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antibodies are derived from maternal or therapeutic sources (colostrum)
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adoptive immunization
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antibodies are transferred from one individual to another (experimental)
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killed vaccines
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agent proteins incapable of replication that stimulate appropriate antibodies
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modified live vaccines
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nonvirulent strains of the agent that stimulate appropriate antibodies
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toxoids
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harmless derivatives of toxins that stimulate antibodies to counter toxic effects
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Jonas Salk
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developed polio vaccine (killed vaccine- 1954)
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Albert Sabin
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developed oral polio vaccine
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herd immunity
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resistant individuals buffer susceptibles from effective contact with infected individuals
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ring vaccination
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individuals in close proximity to symptomatic cases are vaccinated to protect susceptible individuals from exposure to create herd immunity in the population
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cervical cancer mortality has dramatically declined due to
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pap test in picking up cervical dysplasia
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reproducibility
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repeatability or consistency of the test
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validity
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precision or accuracy of the test
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reproducibility (kappa)
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closer you get to 1, the higher the reproducibility
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interpretation of kappa in terms of agreement
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>0.75 (excellent), 0.4-0.75 (fair to good), < 0.4 (poor)
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clinical screening tests are
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simple, rapid, inexpensive, safe, acceptable to the public, accurate
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sensitivity
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proportion of subjects with disease who have a positive test result
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specificity
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proportion of subjects without disease who have a negative test result
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positive predictive value
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proportion with a positive test who have a disease
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negative predictive value
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proportion with a negative test who do not have the disease
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two stage screening tests
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used for early detection of disease - stage 1: high sensitivity to include all cases, stage 2: high specificity to exclude normals (case wide net with high sensitivity, sort out true positives from false positives with high specificity)
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prevalence does not effect
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sensitivity and specificity
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predictive value positive and predictive value negative are
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inversely related
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as prevalence decreases
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predictive value positive decreases and predictive value negative increases
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as specificity increases
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predictive value positive increases and predictive value negative decreases
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international classification of disease (ICD)
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meets the epidemiologist's need for consistency in coding required for national comparisons of disease trends worldwide
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disease incidence
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probability ranging from 0 to 1 that quantifies the risk of contracting disease
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disease odds
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ratio from 0 ro infinity that quantifies the odds of contracting the disease versus remaining healthy
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incidence rate (density)
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new cases/person years (quantifies the rate of contracting disease per unit time)
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uni-cohort
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number of individuals under observation for a specific time interval needed to detect one case (1/incidence rate)
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mortality rate
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rate of death per unit of time (number of deaths/population at risk x years of observation)
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prevalence
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proportion of individuals in a population who have a disease during a specific period of time
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incidence characteristics
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new onsets only, independent of duration, rate/proportion, risk of developing disease, study disease etiology
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prevalence characteristics
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counts new and old onsets, dependent on duration, proportion, risk of having disease, assess health services
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age adjustment - direct method
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obtain age specific disease rates in the target populations under study, obtain age distribution, multiply age specific rates by age distribution to obtain expected rates, compare expected rates for target populations
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age adjustment - indirect method
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obtain crude rates for target population, obtain age distributions for target population, obtain age specific rates for population, compute standard rate ratios for target population and compare
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incidence rate difference
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compares incidence rate of disease for individuals exposed with the incidence rate of disease for those not exposed (IRD = IR(exposed) - IR(non exposed)
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relative risk
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ratio of incidence rate for exposed to incidence rate for non exposed (best calculated from estimates of incidence that have been adjusted for age and other important factors)
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relative risk = 1.0
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rates do not differ
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relative risk > 1.0
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exposure increases risk
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relative risk < 1.0
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exposure decreases risk
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relative risk difference
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(relative risk) - 1 x 100
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agreement of relative risk and odds ratio
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if the incidence of disease is low (<5%) for exposed and unexposed), there will be reasonably close agreement between the relative risk and the odds ratio
