Epidemiology IV: Incidence & Prevalence

Vocabulary practice flashcards covering measures of morbidity, incidence, prevalence, their calculation formulas, and epidemiological applications.

Morbidity

Any departure from a state of wellbeing, encompassing illness, disease, or injury.

Three Aspects of Morbidity

The three components used to measure morbidity: Disease Frequency (evaluated by incidence and prevalence rates), Severity (evaluated by case fatality rate), and Duration (evaluated by disability rate).

Uses of Morbidity Data

1. Describing the extent, nature, load, burden, or magnitude of disease in a community for priority setting; 2. Providing comprehensive information on patient characteristics to assist research; 3. Monitoring and evaluating disease control and preventive activities.

Case

A diseased individual or person in a population who possesses a specific health condition.

Population at Risk

The proportion of a population that is susceptible to a disease and currently disease-free.

Incidence

The number of NEW cases of disease (or other health-related phenomenon) that occur during a specified period of time in a population at risk, serving as a measure of risk.

Incidence Rate Formula

$\frac{\text{NEW cases during given time in specific pop}}{\text{Pop at risk during specific time}} \times 1000$, expressed as the number of cases per year per $1000$ population (where $1000$ is an arbitrary multiplier influenced by disease frequency).

Steps to Calculate Incidence

1. Count cases (identifying NEW cases of disease); 2. Identify the population at risk; 3. Specify the time period; 4. Select the appropriate multiplier.

Attack Rate

A special form of incidence rate used when a population is exposed to risk for a limited period of time, such as during an epidemic or outbreak, to determine the extent of the event.

Attack Rate Formula

$$\frac{\text{New cases of specific disease in a specific time interval}}{\text{Population at risk during same interval}} \times 100$$

Uses of Incidence Rate

1. Measures risk; 2. Aids research into disease aetiology, pathogenesis, and distribution; 3. Assists in disease control; 4. Evaluates the efficacy of preventive and therapeutic measures.

Prevalence

A measure of the total number of all individuals (both new and old cases) who have an attribute or disease at a particular time divided by the population at that time or midway through the period, typically expressed as a percentage.

Steps to Calculate Prevalence

1. Count cases (both OLD and NEW); 2. Define the population in the denominator; 3. Specify the time; 4. Use $100$ as the multiplier.

Point Prevalence

The proportion of all current cases (both old and new) of a specified disease existing at a given single point in time relative to the estimated population at that same point (e.g., assessed by asking 'Do you currently have asthma?').

Point Prevalence Rate Formula

$$\frac{\text{Number of all current cases (old and new) of a specified disease existing at a given point in time}}{\text{Estimated population at the same point in time}} \times 100$$

Period Prevalence

The proportion of individuals who had a specified disease (old and new cases) at any time during a specified duration or interval (e.g., assessed by asking 'Have you had asthma during last (n) year/s?').

Period Prevalence Rate Formula

$$\frac{\text{Number of existing cases (old and new) of a specified disease during a given period of time interval}}{\text{Estimated mid-interval population at risk}} \times 100$$

Uses of Prevalence

Estimating the overall magnitude, load, or burden of disease to identify populations at risk, and guiding administrative and healthcare planning (e.g., human resources, hospital beds, facilities); it is not used to identify the cause of disease.