Epidemiology Core Concepts (Chapters 1-3)

Vocabulary flashcards covering core epidemiological concepts, dynamics of disease transmission, and measures of morbidity and disease occurrence.

Epidemiology

The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to prevent and control disease and promote health.

Primary Prevention

An action taken to prevent the initial development of a disease in a person who is well and does not yet have the disease in question (e.g., immunization).

Secondary Prevention

Early detection of existing disease in individuals who have not yet developed clinical signs or symptoms, aiming to reduce disease severity and complications (e.g., cancer screening).

Tertiary Prevention

Interventions aimed at reducing the impact of disease by preventing complications in individuals who have already developed clinical signs and symptoms and been diagnosed (e.g., stroke rehabilitation).

Etiology

The cause, set of causes, or manner of causation of a disease or condition.

Ignaz Semmelweis

The physician who demonstrated in the 1840s that childbed (puerperal) fever mortality was caused by medical staff transmitting disease from autopsies, and drastically lowered maternal mortality by implementing mandatory handwashing.

Edward Jenner

The physician who developed the smallpox vaccine in the late 1700s by inoculating individuals with cowpox ($\text{vacca}$), demonstrating that mild cowpox infection conferred immunity against smallpox.

Epidemiologic Triangle

A classical model of infectious disease transmission illustrating the essential interaction among three key components: Host, Agent, and Environment, centered around a Vector.

Vector

An organism (such as an insect or animal) that does not cause disease itself, but transmits infection by conveying pathogens from one host to another.

Vehicle

An inanimate object or contaminated material (such as food, water, or utensils) that indirectly transmits an infectious agent to a host.

Preclinical Disease

A disease state that is not yet clinically apparent but is destined to progress to clinical disease.

Subclinical Disease

A disease state that is not clinically apparent and is not destined to become clinically apparent, lacking observable signs or symptoms.

Latent Disease

An infection characterized by the persistence of the pathogen without active multiplication, such as when only the genetic message is present in the host.

Carrier

An individual who harbors an organism without clinical illness or a detectable antibody response, but who can still transmit the infection to others.

Endemic

The habitual or regular presence of a disease within a given geographic area or population group at expected background levels.

Epidemic

The occurrence in a community or region of a group of illnesses of similar nature clearly in excess of normal expectancy.

Pandemic

A worldwide epidemic affecting populations across vast geographic regions.

Herd Immunity

The resistance of a group of people to an infectious disease because a large proportion of the population is immune, effectively blocking transmission to non-immune individuals.

Active Immunity

Long-lasting immunity produced by the host's own immune response following exposure to an antigen (via infection or vaccination), leading to the formation of memory B and T cells.

Passive Immunity

Short-term immunity achieved through the receipt of antibodies produced outside the host (such as maternal transfer via placenta/milk or gamma globulin injection), without activating the host's immune system or forming memory cells.

Incubation Period

The time interval from the initial receipt of infection to the onset of clinical illness marked by recognizable signs and symptoms.

Attack Rate

A measure of cumulative incidence used in outbreak investigations, calculated as the total number of new cases divided by the population at risk ($\frac{\text{number affected}}{\text{number exposed}}$()).

Morbidity

Any state of living with disease, illness, or disability within a population.

Mortality

The occurrence or frequency of death within a specific population over a given timeframe.

Surveillance

The ongoing systematic collection, analysis, and interpretation of health data essential to public health practice, closely integrated with timely dissemination to decision-makers.

Passive Surveillance

A surveillance mechanism relying on available routine reporting structures and data submitted by health care workers and facilities without active recruitment or field solicitation.

Active Surveillance

A surveillance system in which dedicated project staff are specifically deployed to gather disease data directly from healthcare providers and the public.

Incidence Rate

A measure of disease risk calculated as the number of new cases occurring in a population during a specified time period divided by the total person-time at risk.

Person-Time

The sum of individual time units (such as person-years) during which each participant in a study population was observed and remained free of the outcome of interest.

Point Prevalence

The proportion of a population that has a disease at a specific, single point in time.

Period Prevalence

The proportion of a population that has experienced a disease at any point during a specified period of time.

Relative Risk

Also known as the Risk Ratio (RR), it is the ratio comparing the incidence rate of disease among individuals exposed to a factor to the incidence rate among unexposed individuals ($\text{RR} = \frac{\text{IR}_{\text{exposed}}}{\text{IR}_{\text{unexposed}}}$).