Key Terms

Key Terms

Last Update: August 31, 2020


A person who does not show any signs or symptoms of a disease. People with asymptomatic infection feel well. Because they feel well, they don’t know they’re infected, and they often continue their regular activities, which can easily transmit the virus to others.


Asynchronous instruction involves faculty providing material online, but does not include the faculty and class meeting virtually together at a particular time. Faculty might upload slide presentations (PowerPoint, Keynote, or Google Suite), video-recorded lectures accompanied by slides or notes, student assignments, etc. Students then access the material and complete work as required according to a schedule provided by faculty. Exams may sometimes be taken during a particular time window.

The Centers for Disease Control and Prevention (CDC)

The United States' federal health protection organization. 


A collection of cases occurring in the same place at the same time. 


Similar in meaning as "contagious." Used to describe diseases that can be spread or transmitted from one person to another.

Community spread

Circulation of a disease among people in a certain area with no clear explanation of how they were infected—they did not travel to an affected area and had no close link to another confirmed case. This is sometimes referred to as community transmission.

Confirmed case of COVID-19

Someone tested and confirmed to have COVID-19.


A well person who has been exposed to a case or a case’s environment such that they had an opportunity to acquire the infection. According to the Chicago Department of Public Health, a close contact is defined as anyone who was within 6 feet of an infected person for at least 15 cumulative minutes over the course of a day starting from 48 hours before the person began feeling sick until the time the patient was isolated.

Contact Tracing

Contact tracing is used by health departments to prevent the spread of infectious disease. In general, contact tracing involves identifying people who have an infectious disease (cases) and their contacts (people who may have been exposed) and working with them to interrupt disease transmission.

Coronaviruses (CoVs) 

A family of related viruses, many of which cause respiratory illnesses. Coronaviruses cause COVID-19, SARS, MERS, and some strains of influenza, or flu.


The name of the illness caused by the coronavirus SARS-CoV-2. COVID-19 stands for "coronavirus disease 2019.” 

Droplet transmission

A form of direct transmission, i.e., a spray containing large, short-range aerosols (tiny particles suspended in air) produced by sneezing, coughing, or talking. Droplet transmission occurs—in general and for COVID-19—when a person is in close contact with someone who has respiratory symptoms.  


The baseline, or expected, level of the disease in the community—meaning it always exists, like the common cold and flu, which are usually at low, predictable rates.


This refers to a sudden increase in the number of cases of a disease, above what is typically expected in a particular area.


The branch of medicine that studies how diseases happen and spread in communities of people. A person who studies epidemiology is called an epidemiologist.

Flattening the curve

Controlling the rate of new cases of COVID-19. The “curve” refers to a graph showing the number of cases of COVID-19 that happen over a period of time. Many cases happening in a short period of time create a graph that looks like a tall spike. By using protective measures, we can slow down how many new cases happen. This is the “flattening” of the curve—on the graph, the flattened curve winds up looking more like a gentle hill. Flattening the curve reduces the numbers of people needing healthcare at one time. This allows hospitals to treat patients throughout the pandemic.

Hand hygiene

A key strategy for slowing the spread for COVID-19. Washing hands with soap and water for at least 20 seconds is one of the most important steps to take to protect against COVID-19 and many other diseases.

High-risk subpopulation 

A segment of the population that has characteristics that increase the risk of infection or severe disease. 


Your body's ability to resist or fight off an infection. Your immune system is a network of cells throughout your body that help you avoid getting infected and help you get better when you are infected.


Also called immune-compromised or immunodeficient. This describes someone who has an immune system that can't resist or fight off infections as well as most people. This can be caused by several illnesses. Some treatments for illnesses can also cause someone to be immunocompromised.

Incubation period 

The interval between the time of invasion by an infectious agent and appearance of the first sign or symptom of the disease in question. For SARS-CoV-2, the incubation period is on average four to five days but may be as long as 14 days. 

Infectious period 

Period of time during which a case is able to transmit a disease to others. The infectious period starts two days before someone develops symptoms. 


Isolation separates sick people with a contagious disease from people who are not sick.
Isolation occurs under conditions (for example, having a private bedroom and bathroom) that will prevent or limit the transmission of an infectious agent to those who are susceptible. A confirmed case of COVID-19 (someone who has tested positive for the virus) should be isolated for the entirety of their infectious period.

N95 respirator

Sometimes casually referred to as an “N95 mask,” this personal protective equipment is worn on providers’ faces, forming a tight seal around the nose and mouth. Though it looks like a surgical mask, an N95 is actually a respirator that filters out at least 95 percent of particles in the air. According to the CDC, an N95 respirator is recommended only for use by healthcare personnel (HCP) who need protection from both airborne and fluid hazards (e.g., splashes, sprays). These respirators are not used or needed outside of healthcare settings.


This shares the same definition as epidemic (a sudden increase in the number of cases of a disease, above what is typically expected in a particular area), with one exception—an outbreak usually refers to a more limited geographic area.   


An epidemic that has spread over several countries or continents, impacting many people. Pandemics typically happen when a new virus spreads easily among people who—because the virus is new to them—have little or no pre-existing immunity to it.

PCR test 

Short for polymerase chain reaction. A PCR test is a diagnostic test that identifies a virus in the body. SARS-CoV-2 has DNA and RNA sequences that are unique and specific to the virus—that is, no other virus or organism has these sequences. The SARS-CoV-2 PCR test assesses for these sequences. If they are present, the test is positive. It is important to recognize that this is not a culture; these tests just assess for the nucleic acid sequences. PCR tests for SARS-CoV-2 are usually done from swabs taken from the back of the throat or nose.

Personal protective equipment (PPE)

“Specialized clothing or equipment, worn by an employee for protection against infectious materials,” as defined by the Occupational Safety and Health Administration (OSHA). In health care settings, PPE may include gloves, gowns, aprons, masks, respirators, goggles, and face shields. The CDC provides recommendations for when and what PPE should be used to prevent exposure to infectious diseases.


Unlike isolation, quarantine involves separating and restricting the movements of people who were exposed to a contagious disease to see if they become sick. The government may impose a quarantine on someone who was exposed to COVID-19 to avoid spread of the disease to others if they get sick.

Respiratory droplets 

These are particles of respiratory secretions that are exhaled and typically consist of water-like fluid. If someone is infected with SARS-CoV-2, their respiratory droplets will contain SARS-CoV-2 virus, and these are infectious. Respiratory droplet particles cannot float in the air; they will drop to the ground by gravity. Therefore, after a person exhales them, they fall within three to four feet. From a technical standpoint, these particles are defined as >five microns in diameter.


The virus that causes the illness we call COVID-19. 


This step helps health care workers to decide if you actually need a coronavirus test. It’s a series of basic questions about your health condition and recent history. Screening may also include other common healthcare procedures, like taking your temperature.


Separating yourself when you’re sick from healthy individuals to prevent spreading illness. This is different from quarantine, which according to the CDC, separates and restricts the movement of people who were exposed to a contagious disease to see if they become sick.


Checking yourself for COVID-19 symptoms, including fever, cough, or difficulty breathing. If you notice symptoms, you should self-isolate and seek advice by telephone from a health care provider or local health department to determine whether you need a medical evaluation.

Signs of illness 

A health effect that can be observed externally, such as temperature, sweating, oxygen saturation, or heart rate. Signs are also abnormal findings on a physical examination that are observed or measured by a clinician (a physician or nurse). Some signs mean that the disease is becoming more severe or progressing.

Social distancing

Putting physical distance between yourself and other people. This means avoiding groups of people (parties, crowds on sidewalks, lines in a store) and maintaining distance (approximately six feet) from others when possible. 


One person who, for unknown reasons, can infect an unusually large number of people. Infectious disease specialists say it is common for super-spreaders to play a large role in the transmission of viruses. In what's known as the 80/20 rule, 20 percent of infected patients may drive 80 percent of transmissions.


When a person shows signs of illness. A full list of symptoms can be found on the CDC website.

Symptoms of illness 

A health effect that is experienced or felt by the person and is not easily observable by others, such as fatigue or muscle aches. Some symptoms mean that the disease is becoming more severe or progressing.


Synchronous instruction involves faculty and students meeting virtually at a scheduled time. Most synchronous instruction will involve streaming audio/video, but a live text or group chat would also fall in this category. Faculty will often use video conferencing software such as Zoom and Google Hangouts for delivering synchronous instruction. Other materials such as homework and instructions for projects will be made available on Canvas or by email.


A vaccine triggers the immune system to help it build immunity to a disease. The immune system already has the capacity to react to diseases by producing substances called antibodies that remain in the body to fight them in the future. With a vaccine, you don’t have to get the disease to develop immunity—the vaccine triggers the same process by providing the body with a tiny amount of a germ that has been weakened or killed, but small enough that it won’t make you sick. Vaccines are introduced to the body via injection, mouth, or a nasal spray. Currently, there is no vaccine for COVID-19. 

World Health Organization (WHO)

This United Nations organization monitors and protects public health around the world.


Centers for Disease Control and Prevention. “Frequently Asked Questions.” Accessed July 27,  

Centers for Disease Control and Prevention. “Personal Protective Equipment: Questions and 
Answers.” Accessed July 28,  2020.

Centers for Disease Control and Prevention. “Quarantine and Isolation.” Accessed July 28,  

Johns Hopkins University. “COVID-19 Contact Tracing. ” Accessed July 27, 2020. Copyright © 
2020 Johns Hopkins University and Emily Gurley.

Katella, Kathy, “Our New COVID-19 Vocabulary—What Does It All Mean?,” Yale Medicine,  
April 7, 2020,

UVA Health. “Coronavirus & COVID-19: Glossary of Terms.” Accessed July 27, 2020,