mastered dd terms

Disease

An infection that results in objective signs and subjective symptoms.

Opportunistic disease

A disease that causes sickness when given the opportunity by a damaged or weakened immune system.

Nosocomial disease

An infection acquired in a hospital or healthcare setting.

Iatrogenic disease

An illness unintentionally caused by medical treatment, medication, or a physician.

Chronic infection

An infection in which the infectious agent is continuously present and detectable.

Latent infection

An infection in which the agent remains present but can become dormant before reactivation.

Incubation period

The time between exposure to an infectious agent and the first appearance of symptoms or signs.

Latent period

The time between contact with a pathogen and becoming infected.

Asymptomatic

Showing no signs or symptoms despite being infected and potentially able to transmit disease.

Susceptibility

The extent to which an individual or population is able to resist infection.

Susceptible individual

A member of a population who is at risk of becoming infected.

Pathogenicity

The ability of an infectious agent to cause clinical disease after infection.

Virulence

The ability of an infectious agent to cause severe disease.

Infectivity

The ability of an infectious agent to establish an infection after exposure.

Morbidity

Any departure from normal physiological or psychological well-being; in population measures, the occurrence or rate of disease.

Mortality

The rate or occurrence of death in a population.

Case fatality rate (CFR)

The proportion of individuals with a disease who die from that disease.

Prevalence

The proportion or amount of existing disease in a population at a given time.

Point prevalence

Prevalence measured at a single point in time.

Period prevalence

Prevalence measured over a specified interval of time.

Incidence

The occurrence or rate of new cases in a population over a specified period.

Incidence proportion

The proportion of an initially disease-free population that develops new disease during a specified period; also called risk or attack rate in outbreak settings.

Attack rate

The incidence proportion used commonly in outbreak investigations; cases among the population at risk.

Secondary attack rate

The proportion of susceptible contacts who develop disease after exposure to a primary case.

Person-time

The total amount of time that individuals in a population are observed while at risk for disease.

Person-year

One person being observed for one year while at risk for disease.

Person-time rate

The number of new cases divided by the total person-time observed.

Ratio

A comparison of two values; the numerator and denominator do not have to be related.

Proportion

A comparison of a part to the whole; the numerator is always included in the denominator.

Rate

The frequency of an event in a defined population over a specified period of time.

Risk

The probability that an individual will develop a disease or health outcome during a specified period.

Crude death rate

Deaths from all causes divided by the mid-year population.

Cause-specific death rate

Deaths from one specific cause divided by the mid-year population.

Age-specific death rate

Deaths in a specific age group divided by the population in that age group.

Infant mortality rate

Deaths among infants under 1 year of age divided by live births, usually multiplied by 1,000.

Neonatal mortality rate

Deaths among infants under 28 days of age divided by live births, usually multiplied by 1,000.

Death-to-case ratio

The number of deaths divided by the number of new cases; unlike CFR, this is a ratio rather than a proportion.

Proportionate mortality

The proportion of all deaths attributable to a particular cause during a specified period.

Proportionate mortality ratio (PMR)

A comparison of proportionate mortality between two groups.

Age-adjusted mortality rate

A mortality rate statistically adjusted to account for differences in age distributions between populations.

Years of potential life lost (YPLL)

The total years lost when people die before a selected age or endpoint.

YPLL rate

YPLL divided by the population below the selected endpoint age, usually multiplied by a standard constant.

Risk ratio (RR)

The risk in the exposed group divided by the risk in the unexposed group; also called relative risk.

Rate ratio

The rate in one group divided by the rate in a comparison group.

Odds ratio (OR)

A measure of association calculated from a 2×2 table as (a×d) ÷ (b×c); commonly used in case-control studies.

Rare disease assumption

When a disease is uncommon, the odds ratio provides a reasonable approximation of the relative risk.

Two-by-two table

A cross-tabulation showing exposure status against disease status.

Attributable proportion

The fraction or percentage of disease among exposed people that can be attributed to the exposure.

Attributable risk (AR)

The amount of disease incidence associated with an exposure, calculated as risk in exposed minus risk in unexposed.

Healthy worker effect

The tendency for employed workers to have lower disease or death rates than the general population because workers are generally healthier.

Vaccine efficacy

The proportionate reduction in disease among vaccinated people compared with unvaccinated people under ideal conditions.

Vaccine effectiveness

The proportionate reduction in disease among vaccinated people compared with unvaccinated people under real-world conditions.

Index case

The first identified or documented case of a disease in a particular setting.

Etiology

The cause or causes of a disease.

Pathology

The study of the causes, mechanisms, effects, and diagnosis of disease and injury.

Determinant

Any factor that brings about a change in a health condition.

Herd immunity

Protection of a population that occurs when a sufficiently large proportion of the population is immune, reducing transmission and protecting susceptible people.

Fulminant

Having a sudden and severe onset.

Quarantine

Separation or restriction of people who may have been exposed to a disease but are not known to be infected.

Isolation

Separation of people who are known or suspected to be infected from people who are not infected.

Epidemiology

The study of the distribution and determinants of health-related states or events in specified populations and the application of that study to control health problems.

Distribution

The frequency and pattern of health events according to person, place, and time.

Descriptive epidemiology

The characterization of disease by person, place, and time.

Analytic epidemiology

The testing of hypotheses about relationships between exposures and health outcomes, typically using a comparison group.

Case definition

A standardized set of criteria used to classify whether a person is a case of a particular disease or health condition.

Cohort study

An observational study in which people are grouped according to exposure and followed to compare disease outcomes.

Case-control study

An observational study that begins with people who have the disease and people who do not, then compares their previous exposures.

Cross-sectional study

A study that measures exposure and health outcome at the same time; commonly measures prevalence.

Ecological study

An observational study that analyzes data at the population or group level.

Experimental study

A study in which researchers actively assign an exposure, treatment, or intervention.

Randomized controlled trial (RCT)

An experimental study in which participants are randomly assigned to different intervention or control groups.

Observational study

A study in which researchers observe exposures and outcomes without assigning the exposure.

Ecological fallacy

The error of making individual-level conclusions from population-level or aggregate data.

Comparison group

A group used as a reference when evaluating the relationship between an exposure and an outcome.

Control

A person without the disease who serves as the comparison group in a case-control study.

Case-patient

A person who meets the criteria for being classified as a case in an epidemiologic investigation.

Primary case

The first case of a disease introduced into a population or group.

Case ascertainment

The process of identifying people who meet a case definition.

Confirmed case

A case meeting the criteria for confirmation, often including laboratory evidence.

Probable case

A case meeting specified clinical and/or epidemiologic criteria but lacking definitive confirmation.

Suspected case

A person who meets basic criteria suggesting the disease but does not meet the requirements for a probable or confirmed case.

Loose case definition

A broad case definition designed to capture as many possible cases as possible.

Tight case definition

A narrow case definition designed to identify true cases with greater specificity.

Natural history

The progression of a disease through its stages without treatment or intervention.

Epidemiologic triad

The traditional infectious-disease model of causation consisting of agent, host, and environment.

Sufficient cause

A complete set of component causes that together is sufficient to produce a disease or health outcome.

Necessary cause

A factor that must be present for a particular disease or health outcome to occur.

Component cause

A factor that contributes to a sufficient cause but is not necessarily sufficient by itself to cause disease.

Risk factor

A characteristic, exposure, or behavior associated with an increased likelihood of disease.

Exposure

Contact with a factor that may influence the risk of developing a health outcome.

Health outcome

A disease, illness, injury, death, disability, or other measurable health event.

Agent

A biological, chemical, physical, or other factor capable of causing disease.

Host

An organism that can harbor an infectious agent and potentially become infected or affected.

Environment

External conditions or factors that influence disease occurrence or transmission.

Reservoir

The habitat in which an infectious agent normally lives, grows, and multiplies.

Source

The person, animal, object, or substance from which an infectious agent is acquired.

Vector

A living organism that transmits an infectious agent between hosts.

Fomite

A contaminated nonliving object that can help transmit an infectious agent.

Portal of exit

The route through which an infectious agent leaves its reservoir or host.

Portal of entry

The route through which an infectious agent enters a susceptible host.