- agent
- something physical, chemical, nutritional, psychosocial, or biologic that can cause a health issue; must be present for a disease to occur
- airborne transmission
- 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
- alpha
- the p value or the significance level for the results of a study to be deemed statistically significant
- analytic epidemiology
- 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
- attack rate
- the proportion of a population that develops an illness during an outbreak (synonym of incidence proportion)
- attributable risk (AR)
- a measurement of the amount of disease among exposed individuals that is attributed to the exposure
- bias
- 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
- carriers
- individuals with incubating disease or preclinical infection but without overt symptoms who are still capable of transmitting disease
- case-control study
- 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
- case-fatality rate
- the proportion of individuals with a disease who die from it
- causality
- the relationship between cause and effect
- chain of infection
- an epidemiological model that allows for a complex and nuanced interplay between the host, agent, and environment of the epidemiological triad
- chance
- a random error in a study
- clinical disease stage
- stage within the natural history of disease during which signs of the disease develop and diagnosis may occur
- cohort study
- a study in which the investigator documents whether or not study participants were exposed to what is being studied
- confidence intervals
- 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
- confounding
- a type of error that may result in an incorrect causation or conclusion
- cross-sectional study
- 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
- death-to-case ratio
- 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
- descriptive epidemiology
- the frequency and pattern of health events within a population according to the characteristics of person, place, and time
- direct transmission
- transmission of an infectious agent from a reservoir to a host by direct contact or droplet spread of infected material
- droplet spread
- 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
- endemic
- the continual and constant presence of a disease within a given geographic area
- environmental factors
- 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
- epidemic
- when the level of disease in a defined area rises above endemic levels
- epidemiological triad
- 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
- epidemiology
- scientific study of the distribution and determinants of diseases and health outcomes in populations
- experimental studies
- 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
- health events
- disease, injury, or death
- host
- an individual, a family, a group of high-risk individuals, or a community within the context of the epidemiological triad
- hyperendemic
- persistent high levels of disease in a defined area
- incidence proportion
- the proportion of a population that develops an illness during an outbreak (synonym of attack rate)
- incidence rate
- during a given time period, all new cases of a disease or health condition divided by the population at risk
- indirect transmission
- 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
- morbidity
- having a disease, illness, or medical condition; includes disease, injury, and disability
- mortality rate
- the frequency of death in a defined population during a specific time interval
- natural history of disease
- events that occur before development of a disease, during the course of the disease, and at the conclusion of the disease
- observational studies
- epidemiological studies based on investigator observations of exposure and disease status
- odds ratio (OR)
- 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
- outbreak
- an epidemic affecting a limited geographic area
- p value
- the probability that an observed association could be the result of random error
- pathogenicity
- the ability of an agent to cause disease, influencing disease onset
- portal of entry
- how an agent infects a susceptible host
- portal of exit
- how an agent leaves its home base in the chain of causation/infection
- prevalence rate
- proportion of a population that has a health condition at a certain point in time or over a time interval
- proportion
- a form of a ratio in which the numerator represents a subset of the denominator
- rate ratio
- compares the incidence rates or mortality rates of two groups
- ratio
- a comparison of any two values, calculated by dividing one interval by the other
- relative risk (RR)
- 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
- reservoir
- where the causal agent normally lives and reproduces in the chain of causation
- risk ratio
- synonym of relative risk
- sample size
- the number of participants in a study
- sporadic
- diseases that occur at irregular intervals
- spot map
- 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
- statistical significance
- an assessment for random error in a study
- subclinical disease stage
- the natural history of disease stage after exposure but prior to clinical disease in which individuals have pathologic change but no overt symptoms
- susceptibility stage
- 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