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agent
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something physical, chemical, nutritional, psychosocial, or biologic that can cause a health issue; must be present for a disease to occur
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airborne transmission
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occurs when infectious agents are capable of remaining suspended in air over long distances and long periods of time, in contrast to droplets that fall to the ground within a few feet
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alpha
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the
p
value or the significance level for the results of a study to be deemed statistically significant
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analytic epidemiology
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the study of the causes and effects of diseases or other health events, looking for the
why
and the
how,
attempting to quantify a relationship between two variables
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attack rate
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the proportion of a population that develops an illness during an outbreak (synonym of
incidence proportion
)
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attributable risk (AR)
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a measurement of the amount of disease among exposed individuals that is attributed to the exposure
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bias
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a systematic error that underestimates or overestimates the value of a parameter; a source of error in a study’s outcome arising in the design or conduct of the study, data collection, or data analysis
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carriers
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individuals with incubating disease or preclinical infection but without overt symptoms who are still capable of transmitting disease
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case-control study
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a study design in which investigators enroll a group of individuals with a disease and a group of individuals without the disease and compare previous exposures between the groups
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case-fatality rate
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the proportion of individuals with a disease who die from it
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causality
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the relationship between cause and effect
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chain of infection
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an epidemiological model that allows for a complex and nuanced interplay between the host, agent, and environment of the epidemiological triad
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chance
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a random error in a study
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clinical disease stage
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stage within the natural history of disease during which signs of the disease develop and diagnosis may occur
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cohort study
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a study in which the investigator documents whether or not study participants were exposed to what is being studied
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confidence intervals
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the relative risk (or other risk measure) found in the study and an interval within which the risk would most likely fall if the study were repeated multiple times
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confounding
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a type of error that may result in an incorrect causation or conclusion
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cross-sectional study
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a study in which a sample of individuals from a specified population is enrolled and the exposure and disease outcome are measured simultaneously for each participant; provides a snapshot of any specified population at a given point in time
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death-to-case ratio
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the number of deaths attributed to a disease during a specific period of time divided by the number of new cases of that disease during the same period
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descriptive epidemiology
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the frequency and pattern of health events within a population according to the characteristics of person, place, and time
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direct transmission
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transmission of an infectious agent from a reservoir to a host by direct contact or droplet spread of infected material
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droplet spread
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infected material transmitted by direct spray of relatively large, short-range aerosols of the pathogen over a few feet prior to the droplets falling to the ground
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endemic
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the continual and constant presence of a disease within a given geographic area
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environmental factors
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in the epidemiologic triad, the biologic environment of plants, animals, and toxins, including vectors that carry infectious agents and the reservoirs where infectious agents are normally found
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epidemic
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when the level of disease in a defined area rises above endemic levels
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epidemiological triad
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a model of disease causation; classically describes disease as a result of the relationship between a susceptible host, an external agent, and an environment bringing the host and agent together
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epidemiology
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scientific study of the distribution and determinants of diseases and health outcomes in populations
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experimental studies
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in epidemiology, studies in which the investigator controls or changes the factors thought to cause a health event and then observes what happens to the health state
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health events
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disease, injury, or death
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host
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an individual, a family, a group of high-risk individuals, or a community within the context of the epidemiological triad
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hyperendemic
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persistent high levels of disease in a defined area
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incidence proportion
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the proportion of a population that develops an illness during an outbreak (synonym of attack rate)
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incidence rate
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during a given time period, all new cases of a disease or health condition divided by the population at risk
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indirect transmission
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transmission that occurs when an infectious agent is transmitted from a reservoir to a host by suspended air particles, inanimate objects also known as vehicles, or vector intermediaries
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morbidity
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having a disease, illness, or medical condition; includes disease, injury, and disability
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mortality rate
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the frequency of death in a defined population during a specific time interval
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natural history of disease
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events that occur before development of a disease, during the course of the disease, and at the conclusion of the disease
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observational studies
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epidemiological studies based on investigator observations of exposure and disease status
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odds ratio (OR)
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odds a case was exposed divided by the odds a control was exposed; quantitatively expresses the association between an exposure and a disease or health outcome; most often used to estimate the relative risk in case-control studies when the disease being investigated is rare
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outbreak
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an epidemic affecting a limited geographic area
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p
value
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the probability that an observed association could be the result of random error
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pathogenicity
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the ability of an agent to cause disease, influencing disease onset
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portal of entry
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how an agent infects a susceptible host
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portal of exit
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how an agent leaves its home base in the chain of causation/infection
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prevalence rate
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proportion of a population that has a health condition at a certain point in time or over a time interval
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proportion
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a form of a ratio in which the numerator represents a subset of the denominator
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rate ratio
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compares the incidence rates or mortality rates of two groups
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ratio
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a comparison of any two values, calculated by dividing one interval by the other
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relative risk (RR)
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the ratio of the incidence proportion of the health event in exposed individuals (or the group of primary interest) to the incidence proportion in unexposed individuals (or the comparison group); compares the risk of a health event among one group with the risk among another group; see also risk ratio
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reservoir
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where the causal agent normally lives and reproduces in the chain of causation
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risk ratio
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synonym of
relative risk
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sample size
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the number of participants in a study
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sporadic
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diseases that occur at irregular intervals
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spot map
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a type of epidemiological map that shows the geographic distribution of cases of illness or disease by marking each case with a dot on a map
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statistical significance
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an assessment for random error in a study
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subclinical disease stage
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the natural history of disease stage after exposure but prior to clinical disease in which individuals have pathologic change but no overt symptoms
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susceptibility stage
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the initial interactions between the agent, host, and environment during the pre-pathogenesis period, during which time primary prevention measures could be implemented to prevent disease onset