Epidemiology is the study of the cause, transmission, timing, and distribution of infectious disease episodes, with a focus on recognizing outbreaks, controlling those outbreaks, and treating the infected. Diseases are classified by the scale of the infection. Sporadic diseases have only a few isolated cases, usually in scattered locations. However, epidemics occur as a larger-than-expected number of disease cases occurring over a short time in a geographic region. Pathogens, microorganisms capable of causing disease, enter the body through portals of entry and leave the body to transmit the disease to others via portals of exit. Diseases can spread via direct contact, vertical transmission from parent to offspring, droplets, fomites, vehicles (food, water, air), or vectors (animal carriers). The study of how diseases spread provides a crucial piece of information to determine the most effective way of controlling the propagation of disease.
At A Glance
Epidemiology is the study of the cause, transmission, timing, and distribution of infectious disease episodes, with a focus on recognizing outbreaks, controlling those outbreaks, and treating the infected. Epidemiologists count cases of a particular disease (location, date, people involved) and determine disease rate.
Sporadic diseases occur only occasionally or in scattered incidents, whereas in an epidemic, there are larger-than-expected numbers of cases occurring over a short time in a geographic region. A pandemic is an outbreak that occurs in a large percentage of the world’s population over a vast geographic area.
- Sources from which diseases can be transmitted are called reservoirs of infection and include animals, water, and humans.
Portals of entry are the areas of the body through which a pathogen can enter (e.g., skin, mucous membranes, tissues, and placenta), while portals of exit are the parts of the body from which a patient can transmit the disease (e.g., upper respiratory system, bodily fluids, and stool).
Direct contact transmission requires person-to-person contact and indirect contact transmission involves droplets or fomites (inanimate objects). Vehicles of transmission include food, water, and air. Vectors are organisms that spread disease by carrying the pathogen between an infected individual and a noninfected individual.
Nosocomial, or health care–acquired, infections can be exogenous (external) or endogenous (patient's microbiota).
- Vaccination, vector control, isolation, and quarantine are the most common ways of controlling the spread of disease.