Epidemiology Chapters 1-3 – Flashcards
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John Snow
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Father of modern epidemiology; Cholera
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the study of the distribution and determinants of health-related states or events in specified populations AND the application of this study to control health problems
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Epidemiology
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Influences of Disease Transmission
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(1) Interaction between host and agent/environment/and vector (2) Mode of disease transmission (3) Distribution of severity of disease in community (4) Level of disease-to-immunity in community
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Epidemiologic Triad
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Host-Agent-Environment ; Sometimes Vector
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Modes of Transmission
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(1) Direct (2) Indirect
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Direct transmission
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person-to-person contact
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indirect transmission
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(1) Common vehicle: single exposure / multiple exposures / continuous exposure (2) Vector
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Vertical transmission
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transmission of disease-causing agents from mother-to-child during pregnancy/breastfeeding/infections
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Horizontal transmission
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majority of transmissions
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Iceberg Concept
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Ways to measure the impact of disease spread may only capture those diseases that are apparent and may underestimate the potential
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Immune-to-Susceptible Individuals
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Few immune/few infected/many susceptible; By end of day an overwhelmingly infected population and few will be immune
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High level immunity
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Is high level or low level immunity better?
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Herd Immunity
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The resistance of a group of people to an attack by a disease to which a large proportion of the members of the group are immune
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Assumption of herd immunity
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the probability of an infected person encountering every other individual in the population is the same (random mixing)
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(1) Agent: person-to-person transmission/NO VECTOR (2) Strong immunity must result
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Conditions for Herd Immunity
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Endemic
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Habitual Presence
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Epidemic
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Excess of normal expectancy
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Epidemic Curve
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a figure that depicts the distribution of the times of onset of the disease
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Incubation Period
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Time from becoming infected to onset of clinical illness; Sometimes can be determined from an epidemic curve (TIME 0 TO MEDIAN ONSET)
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Unimodal Curve
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Peak; Group of individuals exposed to a common vehicle; Exposure was only one time
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Rates
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Illness / Individuals at risk (for specified period of time)
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Number of people at risk in whom an illness develops / Total number of people at risk
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Attack Rate Equation
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(1) Define the outbreak and validate the existence of an outbreak (2) Examine the distribution of cases by the time and place (Epidemic curve) (3) Look for combinations of relevant variables (4) Develop hypotheses based on existing knowledge/Analogy to know diseases/findings from investigation of outbreak (5) Test Hypotheses (6) Recommend control measures (7) Prepare a written report of the investigation and the findings (8) Communicate findings and implement policies
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Steps in Investigating an Outbreak
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(1) Interaction (2) Modes of Transmission (3) Severity of disease (4) Immune-to-Susceptible in community
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Factors that influence transmission of infectious diseases
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Efficiency
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Advantage of electronic health data records
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(1) Identify the etiology (2) Study the Natural History and prognosis (3) Determine prevalence or measure incidence
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Objectives of Epidemiology
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etiology
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causes of disease
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natural history
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course of disease overtime without intervention
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prognosis
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what to expect after diagnosis
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prevalence
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overall size of problem in the community
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incidence
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how quickly it is growing in the community
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Epidemiological Transition
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transfer from infectious diseases to chronic diseases in population
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(1) Changing Patterns of Disease (2) Prevention (3) Clinical Practice
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Uses of Epidemiological Evidence
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Prevention
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identification of high risk groups and direct preventative measures
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(1) Primary Prevention (2) Secondary Prevention (3) Tertiary Prevention
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Types of Prevention
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Primary Prevention
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prior to disease occurring (ex vaccines)
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Secondary Prevention
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early detection to reduce severity (ex screening)
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Tertiary Prevention
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reducing impact of disease (ex rehabilitation therapy)
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Clinical Practice
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the practice of medicine is dependent on population data
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Intimate Partner Violence
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describes physical / sexual / or emotional harm by a current or former spouse or partner
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US Preventive Services Task Force
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makes clinical recommendations based on evidence
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quantitative
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Epidemiology is primarily a ___________ methodology that includes reasoning
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Biostatistics
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Biology of human disease and exposure into the way we interpret the data
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morbidity
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illness
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mortality
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death
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Incident Case
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New case of a disease in a community during a specified period of time (often calendar year)
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Incidence
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Number of new cases of a disease occurring in an at-risk population during a defined period of time
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Incidence Rate
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Incidence proportion ; Method to estimate the risk of getting disease
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Prevalent Case
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An existing case of a disease in a community during a specified period of time
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Prevalence Rate
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An estimate of the magnitude of the disease burden in a community
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Number of new cases in Population / Number of people at risk in the population
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Prevalence Rate Equation
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Number of NEW cases in population / Number of people AT RISK in population
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Incidence Rate Equation
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Deaths total in population / Population
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All-Cause Crude Mortality Rate Equation
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Deaths from disease / Those who are sick
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Case-Fatality Equation
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Deaths from disease / Total Deaths
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Proportionate Mortality Ratio Equation
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Sir Richard Doll
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Found link between cigarettes and lung cancer
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DA Hnderson
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Led WHO in eradicating small pox
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Miriam Brailey
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TB; First woman faculty member
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Edward Jenner
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Small pox; found that diary maids who had cox pox were immune to small pox
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Ages at individual deaths for those who died in community / Life expectancy
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Years of Potential Life Lost Rate Equation
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Subclinical disease (iceberg)
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(1) Exposure without infection OR (2) Infection without clinical illness (asymptomatic infection)
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Clinical disease (iceberg)
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(1) Classical and severe disease OR (2) Moderate severity mild illness
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Clinical disease
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characterized by signs and symptoms
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Nonclinical disease
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(1) Preclinical disease (2) subclinical disease (3) persistent disease (4) Latent disease
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Preclinical disease
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disease that is not yet clinically apparent but is destined to progress to clinical
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Subclinical disease
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Disease that is not clinically apparent and is not destined to become clinically apparent
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Persistent (chronic) disease
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Infection persists for years or for life
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latent disease
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infection with no active multiplication of the agent
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pandemic
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worldwide epidemic
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Common-vehicle exposure
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if an outbreak occurs to many people from a single source (ex food poisoning)
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single exposure
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outbreak source only occurred once (ex luncheon)
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multiple exposures
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outbreak source is presented more than once (ex food that is served more than once)
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periodic exposures
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source is presented multiple times as a result of a intermittent contaminations (ex water that is contaminated based on changing pressures)
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continuous exposures
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constant source of contamination (ex smog)
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Number of people at risk in whom a certain illness develops / Total number of people at risk
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Attack Rate Equation
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Comparing the risk of disease in groups with different exposures
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Attack rate is useful for:
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primary case
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a person who acquires disease from that expsure
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secondary case
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a person who acquires the disease from a primary case
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secondary attack rate
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the attack rate in susceptible people who have been exposed to a primary case
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cross-tabulation
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when confronted with several possible causes; look at each cause separately
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surveillance
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monitoring changes in disease frequency or levels of risk factors
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epidemiological surveillance (CDC)
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ongoing systematic collection/ analysis/ and interpretation of health data essential to the planning/ implementation/ and evaluation of public health practice closely integrated with the timely dissemination of these data to those who need to know
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passive surveillance
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surveillance in which available data on reportable diseases are used with the responsibility for the reporting often falling on the health care provider or district health officer
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active surveillance
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a system in which project staff are recruited to carry out a surveillance program and engage in case finding
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Number of new cases of a disease in population during time / Number of persons at risk for disease during time
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incidence rate equation
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Number of people exposed to a suspect source who became ill / Number of people who were exposed to that source
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attack rate equation
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Number of cases of a disease present in population at time / Number of persons in population at time
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prevalence equation
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point prevalence
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prevalence of the disease at a certain point in time
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period prevalence
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how many people have had the disease at any point during a certain time period
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(1) Defining who has disease (2) Ascertaining which persons should be included in the numberator
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Problems with numerators
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(1) Selective undercounting of certain groups in population (2) Who is at risk?
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Problems with denominators
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(1) Selective (2) Designed for patient care (3) problems with denominators (who is in hospital)
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problems with hospital data
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Prevalence = Incidence X Duration of Disease
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Relationship between incidence and prevalence
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spot maps
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examing geographic or spatial differences in incidence through plotting the cases on a map
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Total number of deaths from all causes in 1 year / Number of persons in the population that year
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Annual mortality rate for all causes equation
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specific rate
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when a restriction is placed on a rate (ex age)
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disease/cause specific rate
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limiting the rate of deaths to a certain disease
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Number of individuals dying during a specified period of time after disease onset or diagnosis / Number of individuals with specified disease
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Case-fatality equation
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Number of deaths from disease in year / Total deaths in year
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Proportionate Mortality Equation
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Years of Potential Life Lost
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a measure of premature mortality or early death
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(1) For each cause each deceased person's age at death is subtracted from a predetermined age at death (2) the "years of potential life lost" for each individual are added together to yield total for specific cause of death
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Steps to determine Years of Potential Life Lost
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direct age adjustment
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a standard population is used in order to eliminate the effects of any differences in age between two or more populations being compared
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indirect age adjustment
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used when numbers of deaths for each age-specific stratum are not available
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Observed number of deaths per year / Expected number of deaths per year
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Standardized Mortality Ratio Equation
