HOSA Epidemiology

Incidence

The number of new cases per person per unit of time

Prevalence

The proportion of the population at a given time that has a case

Case Fatality Rate

Ratio of fatal cases to total cases, The proportion of persons with the disease who die from it.

Risk factor

A definable element of exposure that captures at least one part of the pathway by which the cause increases the risk that a member of the population will meet the criteria of a case.

Observational Study

Study in which events occur without the scientist having controlled starting conditions. Resembles the studies of geology and astronomy.

Epidemiology

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

5 Ws of Descriptive Epidemiology

Diagnosis or health event (what), Person (who), Place (where), Time (when) and Modes of Transmission (why/how)

Frequency

Not only the number of health events, but also the relationship of that number to the size of the population.

Pattern

The occurrence of health-related events by time, place and person.

Descriptive Epidemiology

Characterizing health events by time, place, and person.

Determinants

The causes and other factors that influence the occurrence of disease and other health-related events.

Analytic Epidemiology

Provides the "why" and "how" disease and other health events spread/occur.

Public Health Surveillance

The ongoing, systematic collection, analysis, interpretation, and dissemination of health data to help guide public health decision making and action.

Field Investigation

Characterizes the extent of the epidemic and attempts to identify its cause.

Shoe Leather Epidemiology

Slang; the objective is to learn more about the natural history, clinical spectrum, descriptive epidemiology, and risk factors of the disease before determining what disease intervention methods might be appropriate.

Analytic Studies

A study with the purpose of identifying and quantifying the relationship between an exposure and an outcome and to test hypotheses about causal relationships by comparing case-patients and those in an appropriate comparison group (control).

Design

Includes determining the appropriate research strategy and study design, writing justifications and protocols, calculating sample sizes, deciding on criteria for subject selection (e.g., developing case definitions), choosing an appropriate comparison group, and designing questionnaires.

Conduct

Involves securing appropriate clearances and approvals, adhering to appropriate ethical principles, abstracting records, tracking down and interviewing subjects, collecting and handling specimens, and managing the data.

Analysis

Begins with describing the characteristics of the subjects. It progresses to calculation of rates, creation of comparative tables (e.g. two-by-two tables), and computations of measures of association (e.g., chi-square test), confidence intervals, and the like.

Interpretation

Involves putting the study findings into perspective, identifying the key take-home messages, and making sound recommendations. Doing so requires the epidemiologist be knowledgeable about the subject matter and the strengths and weaknesses of the study.

Evaluation

The process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to establish goals.

Effectiveness

Refers to the ability of a program to produce the intended or expected results in the field.

Efficacy

The ability to produce results under ideal conditions.

Efficiency

Refers to the ability of the program to produce the intended results with a minimum expenditure of time and resources.

Formative Evaluation

Evaluation that focuses on plans.

Process Evaluation

Evaluation that focuses on operations.

Summative Evaluation

Evaluation that focuses on impact.

Linkages

Working in conjunction with members of other disciplines.

Case Definition

A set of standard criteria for classifying whether a person has a particular disease, syndrome, or other health condition.

Rate

The number of cases divided by the size of the population per unit of time.

Secular trends

Long term trends; Assess the prevailing direction of disease occurrence (increasing, decreasing, or essentially flat).

Epidemic Curve

A graph used to show the time course for a disease outbreak or epidemic.

Experimental Study

In this type of study, the investigator determines through a controlled process the exposure for each individual (clinical trial) or community (community trial), and then tracks the the individual or communities over time to detect the effects of the exposure.

Cohort Study

In this type of study, and epidemiologist records whether each study participant is exposed or not, and then tracks the participants to see if they develop the disease of interest. Similar to an experimental study, but observes rather than determines the exposure status.

Prospective Cohort Study

A kind of cohort study that observes the exposure status, and tracks the participants to see if they develop the disease in question; Also called a follow-up study

Retrospective Cohort Study

In this type of study, both the exposure and the outcomes have already occurred.

Case-Control Study

In this type of study, epidemiologists start by enrolling a group of people with a disease and a group of people with out that disease (controls). Investigators then compare previous exposures between the two groups.

Case-Patient

A person with the disease of interest. Not called a case because case refers to occurrence of disease rather than a person.

Cross-Sectional Study

In this type of study, a sample of persons from a population is enrolled and their exposures and health outcomes are measured simultaneously. It tends to assess the presence (prevalence) of the health outcome at that point in time without regard to duration.

Epidemiologic Triad

Model of disease causation consisting of an external agent, a susceptible host, and an environment that brings the host and agent together. Works best for infectious diseases.

Agent

An infectious microorganism or parasite, chemical contaminants, or physical force that causes disease or injury.

Host

The human who contracts the disease.

Environment

Refers to the intrinsic factors that effect the agent and the opportunity for exposure.

Causal Pie

A model of disease causation that accounts for the multifactorial nature of causation that represents each individual factor as a piece of the pie. After all the piece fall into place - disease occurs.

Necessary Cause

A component that appears in every pie or pathway. Without it, a disease will not occur.

Incubation Period

Name for the time from exposure to onset of disease symptoms for infectious diseases

Latency Period

Name for the time from exposure to onset of disease symptoms for chronic diseases.

Spectrum of Disease

The range of manifestations a disease process can take (e.g., from asymptomatic to mild clinical illness to severe illness and death).

Infectivity

The proportion of exposed person who become infected.

Pathogenicity

The proportion of infected individuals who develop a clinically apparent disease.

Virulence

The proportion of the population of clinically apparent cases that are fatal.

Carriers

Case-patients that are asymptomatic, but can still transmit disease.

Reservoir

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

Zoonosis

An infectious disease that is transmissible under natural conditions from vertebrate animals to humans.

Portal of Exit

The path by which a pathogen leaves its host

Direct Transmission

Transmission in which an infectious agent is transferred from a reservoir to a susceptible host by direct contact or droplet spread

Indirect Transmission

Refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors).

Direct Contact

Contact that occurs through skin-to-skin contact, kissing, and sexual intercourse. Can also refer to contact with soil or vegetation harboring infectious organisms

Droplet Spread

Refers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking.

Airborne Transmission

Occurs when infectious agents are carried by dust or droplet nuclei suspended in air

Vehicles of Transmission

Include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels).

Vectors of Transmission

Examples include mosquitoes, fleas, and ticks that may carry an infectious agent through purely mechanical means or may support growth or changes in the agent

Portal of Entry

Refers to the manner in which a pathogen enters a susceptible host.

Herd Immunity

The concept that suggests that if a high enough proportion of the population are resistant to the agent, then the few that are susceptible will be protected by the resistant majority, since the pathogen will be unlikely to "find" those few susceptible individual.

Endemic

The constant presence of an agent or health condition within a given geographic area or population; can also refer to the usual prevalence of an agent or condition.; Baseline

Sporadic

Refers to a disease that occurs infrequently and irregularly

Hyperendemic

Refers to persistent, high levels of disease occurrence.

Epidemic

Refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.

Outbreak

Refers to a sudden increase in the number of cases of disease above the baseline, often limited to a more limited geographic area.

Cluster

Refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.

Pandemic

Refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people

Common-Source Outbreak

Outbreak in which a group of persons are all exposed to an infectious agent or a toxin from the same source.

Point-Source Outbreak

Outbreak in which a group of persons are all exposed to an infectious agent or a toxin over a relatively brief period of time so that everyone who becomes ill does so within one incubation period.

Continuous Common-Source Outbreak

Outbreaks in which case-patients may have been exposed over a period of days, weeks, or longer, resulting in the flattening and widening of the peaks of the epidemic curve. The range of exposures and range of incubation periods are longer.

Intermittent Common-Source Outbreak

The epidemic curve of this type of outbreak often shows its intermittent nature of this exposure.

Propagated Outbreak

Results from transmission from one person to another. Cases occur over more than one incubation period.

Mixed Epidemic

Epidemic that starts out with a common-source outbreak, followed by person-to-person spread (propagated outbreak).

Distribution

The when (time), place (where), and person (who) of the case.

Public Health Surveillence

Includes includes the collection, analysis, and dissemination of public health information to help guide public health decision making and action

Value

The number or descriptor that applies to a particular person, such as 5'6" (168 cm), female, and never vaccinated.

Attack Rate

The proportion of the population that develops illness during an outbreak; Incidence proportion

Prevalence Rate

The proportion of the population that has a health condition at a point in time

Secondary Attack Rate

Sometimes used to calculate the difference between community transmission of illness versus transmission of illness in a household, barracks, or other closed population.

Point Prevalence

The prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date.

Period Prevalence

The prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attribute at any time during the interval.

Proportionate Mortality Rate

Used to compare deaths in a population of interest (say, a workplace) with the proportionate mortality in the broader population.

Years of Potential Life Lost

Calculated as the sum of the differences between a predetermined end point and the ages of death for those who died before that end point.

Measures of Association

Quantifies the relationship between exposure and disease among the two groups

Relative Risk

Compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group.

Rate Ratio

Compares the incidence rates, person-time rates, or mortality rates of two groups.

Odds Ratio

Quantifies the relationship between an exposure with two categories and health outcome; Cross-Product Ratio

Attributable Proportion

A measure of the public health impact of a causative factor.

Ordinal Variable

Has an intrinsic order, but differences between levels are not relevant.

Discrete Variable

Values are integers (can only be .

Continuous Variables

Can have any value in a range (includes fractions and decimals)

Contingency Table

A two-variable table with data categorized jointly by two variables.

Surveillence

Term applied to almost any effort to monitor, observe, or determine health status, diseases, or risk factors within a population

Syndromic Surveillence

Situation in which the criteria for identifying and counting occurrences of a disease consist of a constellation of signs and symptoms, chief complaints or presumptive diagnoses, or other characteristics of the disease, rather than specific clinical or laboratory diagnostic criteria.

Null Hypothesis

Assuming that the exposure is not related to the disease

Alternative Hypthesis

Assuming that the exposure is related to the disease.