Epidemiology: Incidence and Prevalence II

A set of vocabulary flashcards covering the key definitions, formulas, study types, and determinants of incidence and prevalence in epidemiology.

Prevalence

An epidemiological measure that includes all existing cases (both old and new) in a specified population at a given time point, reflecting the overall burden of disease and typically expressed as a percentage or proportion ranging from $0$ to $1$ ($0\text{--}100\%$).

Incidence

An epidemiological measure of the number of NEW cases of disease that occur in a population at risk during a specified time period, used primarily to evaluate disease risk, etiology, and risk factors.

Prevalence Proportion

A synonym for prevalence that expresses existing cases as a proportion of the entire population at a specific point in time, interpreted on a scale from $0$ to $1$ ($0\text{--}100\%$).

Cumulative Incidence

Also known as risk or incidence proportion; the proportion of an at-risk population at the start of a time interval that develops new disease, interpreted as a probability ranging from $0$ to $1$ ($0\text{--}100\%$).

Incidence Rate

Also known as incidence density, hazard, or person-time rate; a measure with a range from $0$ to infinity, interpreted as the reciprocal of waiting time, calculated using new cases over summed person-years of observation or average population during a time interval.

Point Prevalence

The proportion of a population that has a disease at a single specific point in time, calculated as current cases (both new and preexisting) divided by the population at that same specific point in time.

Period Prevalence

The proportion of a population that has a disease over a defined time interval, calculated as current cases (both new and preexisting) over that period divided by the average or mid-interval population.

Secondary Attack Rate

An epidemiological measure of disease spread defined as the number of new cases among contacts divided by the total number of contacts.

Burden of Disease (BOD)

The quantified impact of disease morbidity measured by prevalence (expressed as a percentage), predominantly utilized by public health authorities for resource allocation and planning healthcare facilities.

Cross-Sectional Study

The observational study design most suitable for determining disease prevalence and assessing healthcare burden in a population at a single point in time.

Longitudinal Study

The study design best suited for establishing incidence, quantifying the rate of new disease onset per $1000$ population, and evaluating risk factors and etiology over time.

$$P = I \times D$$

The mathematical formula showing the relationship between prevalence ($P$), incidence ($I$), and mean duration of disease ($D$), which holds true under the assumptions that the population is stable and both incidence and duration are not changing.

Factors Increasing Prevalence

Epidemiological conditions that raise disease prevalence, including longer duration of illness, prolongation of life without cure, increased incidence (new cases), in-migration of cases, in-migration of susceptible individuals, out-migration of healthy individuals, and improved diagnostic facilities.

Factors Decreasing Prevalence

Epidemiological conditions that lower disease prevalence, including shorter duration of disease, high case-fatality rate, decreased incidence (reduction in new cases), in-migration of healthy individuals, out-migration of cases, and improved cure rates.