COVID-19 Glossary

Browse the glossary using this index

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case fatality rate (CFR)

The number of sick people who die from a specific disease. You calculate case fatality ratio by taking the number of people who have died from a disease and dividing it by the number of people who got that disease.

A CFR can change over space and time. 


Stands for the Centers for Disease Control and Prevention. The CDC is the U.S. agency that tracks diseases across the country, and is responsible for confirming COVID-19 cases. The main lab is in Atlanta, but the agency has other labs around the country where the study of deadly diseases and the search for cures take place.

circulatory system

The system that moves blood through your body. Blood transports nutrients and oxygen.

clinical trial

A designed trial to test the effectiveness of a medication or treatment. Clinical trials include “controls.” A control is a person or group or lab specimen that doesn’t receive the new treatment. The goal is to see if the treatment really works, or if it’s just a placebo effect or caused by something else.

clinically diagnosed

When a person is diagnosed with a disease by their health care provider based on symptoms and risk factors, but they did not have a laboratory test to confirm the diagnosis.

close contact

Being within six feet of a COVID-19 case for a prolonged period of time.

community mitigation

Actions that people and communities can take to help slow the spread of viruses, including seasonal and pandemic influenza.

community spread or community transmission

The spread of a contagious disease within a community. It also has the specific meaning of “the spread of a contagious disease to individuals in a particular geographic location who have no known contact with other infected individuals or who have not recently traveled to an area where the disease has any documented cases.”

confirmed case

A coronavirus case that has been confirmed by the CDC.

contact tracing

The practice of identifying and monitoring individuals who may have had contact with an infectious person as a means of controlling the spread of a communicable disease.


Transmissible by direct or indirect contact with an infected person. Contagious diseases may be spread by direct or indirect contact.

An ailment such as food poisoning is infectious, it is capable of producing infection, but it is not contagious. The coronavirus, on the other hand, is both contagious and infectious. Anything that is contagious is automatically also infectious, but the reverse is not true. Both words are frequently used in a figurative manner.

cordon sanitaire

A measure preventing anyone from leaving a defined geographic area, such as a community, region, or country infected by a disease to stop the spread of the disease.


A group of RNA viruses that circulate in animals and humans. In humans, they cause respiratory illnesses, which means they cause symptoms in the lungs, throat, and airways.  


COVID-19 is “a mild to severe respiratory illness that is caused by a coronavirus,” one that is characterized especially by fever, cough, and shortness of breath and may progress to pneumonia and respiratory failure. The name is an odd sort of acronym, insofar as it is formed from portions of two distinct words (COronaVIrus & Disease) and the latter portion of a date (the 19 from 2019). COVID-19 was first identified in Wuhan, China in December 2019.

CT scan

“Computer Tomography scan.” It’s an advanced type of X-ray that makes a more detailed image. CT scans can help identify suspected coronavirus patients.