COVID-19 Glossary

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An old name for the virus that causes COVID-19. It is now called SARS-CoV-2.




Acute Respiratory Distress Syndrome (ARDS)

An often-fatal failure of the respiratory system. When an illness is called “acute,” it means it comes on really quickly, which makes getting treatment fast necessary. People with ARDS breathe rapidly, are short of breath and might have bluish skin. ARDS is a potential complication of COVID-19, and it can happen very quickly. 

advance directives

Legal documents including the Living Will and Durable Power of Attorney for Health Care — A Living Will states what type of treatment a person wishes to receive in the event they become physically or mentally unable to communicate their wishes. 




The tiny air-filled sacs that make up our lungs. Lungs aren’t like big balloons. They’re more like sponges made up of millions of tiny balloons. There are cells in our alveoli that make a protein that lubricates our lungs and keeps them happy. The COVID-19 virus binds to those cells. Researchers think that may be why the virus is so much more severe than the cold-causing coronavirus.


Kills bacteria — but not viruses. Antibacterial soaps are no more effective than regular soap against viruses like the coronavirus.


A medication that kills bacteria. Antibiotics do not work on viruses, but they are an important part of treating secondary infections like bacterial pneumonia, which can occur as a side-effect of COVID-19.


Antimicrobial products kill most microbes, like viruses, bacteria, and fungi. Hand sanitizer that’s at least 60% isopropyl alcohol is antimicrobial. Some hand sanitizers are only antibacterial and will not protect against coronavirus. 

antiretroviral drugs

These are drugs that attack retroviruses like HIV. Antiretrovirals block or slow down an enzyme that retroviruses use to chop up DNA. If a virus can’t chop DNA, it can’t make more of itself and can’t make you sick. Because coronavirus also uses this enzyme, there was some hope that already existing antiretrovirals could fight the COVID-19 virus. Unfortunately, there’s little evidence that it works on coronavirus. 


When you aren’t showing symptoms. There is some evidence for asymptomatic spread of COVID-19, but those may be cases with mild symptoms that went unreported.


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.



Deoxyribonucleic acid. Many of our genes are stored in DNA. Some are stored in RNA. DNA is a sort of blueprint. It tells our bodies how to grow, assemble themselves, and go about the business of living. Coronaviruses are RNA viruses, so they don’t contain DNA.

drive-through testing

Individuals remain in their vehicles, and medical staff in protective gear come to administer the swab test and the swabs are sent to a laboratory for testing.

droplet transmission/spread

A mode of transmission for a contagious disease that involves relatively large, short-range (less than 6 feet) respiratory droplets produced by sneezing, coughing, or talking.


elective surgeries

Procedures that are considered non-urgent and non-essential. During periods of community transmission, CDC is recommending postponing elective procedures, surgeries, and non-urgent outpatient visits. 


An infection that causes the brain to inflame. It can be extremely dangerous and fatal. Coronaviruses are known to infect the brain, spine and nervous system in lab animals. One case of viral encephalitis was linked to COVID-19, but it is not a major concern with the virus.


An enzyme is a molecule made up of different proteins. They’re molecules that our bodies use to do things. The enzyme myosin makes muscles contract, and the enzyme insulin tells our blood when to absorb sugar. Viruses use enzymes to hijack our cells and make copies of themselves. Many antiviral treatments work by targeting enzymes: to fight a viral infection, you take away the tools a virus needs to make more of itself.


A large outbreak of disease, taking place over a short period of time. An epidemic might infect a region or a country. Epidemics usually happen when a new disease emerges or when something happens to make people less immune to a disease. A pandemic is an epidemic that spreads to multiple large regions, like several continents or countries. 


The study of how infectious diseases spread, occur, and are controlled. John Snow (not to be confused with the character Jon Snow of “Game of Thrones” fame) is considered the founder of modern epidemiology. He famously traced a 19th-century cholera epidemic to a contaminated water pump and the pump handle. He chlorinated the water and removed the pump handle, and the disease ended. Today, sometimes epidemiologists talk about tracing modern diseases back to the metaphorical “Pump Handle.” 

essential activities

Tasks essential to maintain health and safety, such as obtaining medicine or seeing a doctor.

essential government functions

All services needed to ensure the continuing operation of the government agencies and provide for the health, safety and welfare of the public.


flatten the curve

Flattening the curve refers to taking protective actions, often called community mitigation measures, that help slow the spread of a disease so the health care system does not get overwhelmed by having a lot of very sick people all at once. The protective actions can be things like canceling large gatherings, keeping space between people (called social distancing), and continuing to do things like washing hands, covering coughs, and staying home when sick.


Fomite is an object (such as a dish or a doorknob) that may be contaminated with infectious organisms and serve in their transmission.” While this word is infrequently encountered, there has been considerable talk of late about possible surfaces and objects which might harbor infectious substances, and it may well be useful to have this specific word at hand.



An online database of genetic sequences from around the world and maintained by the national library of medicine.



Those considered high-risk include older people or those with certain underlying health conditions. These include blood disorders, chronic kidney disease, chronic liver disease, a compromised immune system, late term or recent pregnancy, endocrine disorders, metabolic disorders, heart disease, lung disease, and neurological conditions.

home isolation

Persons with COVID-19 who have symptoms or laboratory-confirmed COVID-19 who have been directed to stay at home until they are recovered. (Source:



An immune system that isn’t functioning correctly. A person can be immunocompromised by diseases like AIDS or taking some anti-cancer drugs, but also by losing sleep, not drinking enough water and eating poorly. Pregnant women aren’t considered immunocompromised, but changes to their immune system can make them more susceptible to some diseases.


People with immune systems that are (usually artificially) weakened. People with organ transplants take immunosuppressants to stop their immune systems from attacking the organs. Immunosuppressed people are also immunocompromised.

in vitro

A lab test done on cells, not living things. We do in vitro tests on drugs, diseases and chemicals to see how they impact human cells.

in vivo

A lab test on a living organism, whether that’s a plant or an animal or something else. Drugs are usually tested in vivo to make sure they’re safe and that they work.

incubation period

The amount of time it takes for an infected person to start showing symptoms. Most people develop COVID-19 symptoms by day 12, but some people will take longer.

index case

The first documented case of an infectious disease or genetically transmitted condition or mutation in a population, region, or family. It may also refer to an individual who has a disease, condition, or mutation that is the first one identified in a population. This second sense is synonymous with index patient. A related term is patient zero, “a person identified as the first to become infected with an illness or disease in an outbreak.” Patient zero is especially used to refer to a person documented as being the first known case of a communicable disease in a particular population or region.


Producing or capable of producing infection, containing pathogenic agents which may be transmitted. 

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.


When a person who is showing symptoms of a disease separates themselves from other people to prevent spreading the disease to others.


lab-confirmed case

When a person is diagnosed with a disease that is confirmed through having specimens (samples) tested in a laboratory.


martial law

The law administered by military forces that is invoked by a government in an emergency when the civilian law enforcement agencies are unable to maintain public order and safety. 

The martial portion of martial law comes from the Latin word martalis, meaning “of Mars” (referring to the Roman god of war).


Middle East Respiratory Syndrome. Another type of coronavirus, transmitted from camels. MERS is more deadly than COVID-19. It causes noticeable symptoms in most people, so it’s easier to track the virus.

morbidity rate

The number of people who will get sick from a particular cause in a particular population over a certain period of time. To calculate the morbidity rate you would divide the number of sick people in a population by the number of healthy people.

mortality rate

The number of deaths from a particular cause in a particular population over a certain period of time. To calculate the mortality rate, you would divide the number of deaths by the number of sick and healthy people in a population.


N95 respirator (face mask)

Personal protective equipment that is used to protect the wearer from airborne particles and from liquid contaminating the face.

negative-pressure rooms

Rooms specifically designed for patients with contagious diseases that contain any circulating air in the room and prevent it from being released into any other part of the hospital.

novel coronavirus (nCoV)

Any new coronavirus that hasn’t been studied yet or that has just emerged. When SARS-CoV-2 was first found, it was called 2019-nCoV. The SARS-CoV-2 virus causes the disease, which is called COVID-19.



An outbreak is when a disease spreads quickly in a group of people (or animals or plants or …) in one place at one time. When a bunch of people in one town get food poisoning, that’s an outbreak. An epidemic is a really big outbreak, but still just one place at one time.



A global outbreak of disease. Pandemics happen when a new virus emerges to infect people and can spread easily between people.


Stands for Powered Air-Purifying Respirator. They’re the giant full-body suits and helmets healthcare workers wear to treat people quarantined with infectious diseases.


A bacteria, microbe, parasite, fungus, virus or other organism that causes a disease.

personal protective equipment (PPE)

Equipment such as masks and gloves that doctors and nurses wear to protect themselves from diseases.


An infection that causes the tiny air sacs in lungs, called alveoli, to get inflamed and fill with fluid, like mucus or pus. It can be caused by bacteria or viruses. Viral pneumonia can leave the body open for infection from bacterial pneumonia. Right now, bacterial pneumonia is a major complication of COVID-19.

pre-existing conditions

Pre-existing conditions are health conditions someone already has that could make a coronavirus infection worse. Lung disease, asthma and heart disease are pre-existing conditions


A scientific study that is posted online before it has gone through peer-review. Some preprints are good; some are bad. There’s very little quality control. Because peer-review can take a long time, many studies published on coronavirus will be released as preprints. 

presumptive case

A coronavirus case identified by a testing organization. Although other groups can do tests for coronavirus they won’t be considered a confirmed case until the CDC checks the data.


Person Under Investigation. These are people with COVID-19-like symptoms who are not confirmed to have the virus. PUIs can be individuals who had contact with a confirmed case and are displaying some symptoms or they can be people who were hospitalized with severe pneumonia without a different explanation.


Something involving lungs. A pulmonary disease is a lung disease.

pulmonary ventilation

The respiratory system aids in breathing, also called pulmonary ventilation. In pulmonary ventilation, air is inhaled through the nasal and oral cavities (the nose and mouth). It moves through the pharynx, larynx, and trachea into the lungs. Then air is exhaled, flowing back through the same pathway. Changes to the volume and air pressure in the lungs trigger pulmonary ventilation.


Person under monitoring. A individual who does not have COVID-19 symptoms but who has been in contact with someone who is presumed or confirmed to have the virus. A PUM is “monitored” until they’ve gone a period of time without developing symptoms.



Currently most often found with the meaning of “a restraint upon the activities or communication of persons or the transport of goods designed to prevent the spread of disease or pests.” The word has a number of other meanings, both archaic and current, many of which have to do with a period of 40 days (it may be traced back to the Latin word quadraginta, meaning “forty”).



In epidemiology, an R0 is a measure of transmission. It basically represents the average number of people that one infected person will, in turn, infect. Based on current information, coronavirus has an R0 somewhere between 2 and 3, so the average infected person will pass the virus on to two or three more people. That makes it more contagious than the flu, which has an R0 of about 1.5. Measles, one of the most contagious viruses, has an R0 of about 15.

R0 / reproductive rate

An epidemiological metric used to describe the contagiousness or transmissibility of infectious agents, which is usually estimated with complex mathematical models developed using various sets of assumptions. It is an estimate of the average number of new cases of a disease that each case generates, at a given point in time. 


An antiviral that may work against coronavirus. It is currently in clinical trials but for bureaucratic and scientific reasons those trials may not be considered valid in the U.S.

respiratory illness

A disease that impacts lungs, throat and airways. Respiratory illnesses primarily cause coughing, fever and can lead to severe pneumonia. Most are spread in respiratory droplets, which are virus-filled drops of water we shoot out when we cough and sneeze. Although respiratory illnesses attack airways, they can ultimately damage a number of other organs.

respiratory system

The entire system that lets you breathe. Not just your lungs, but your nose, your airways, your trachea, your mouth and your diaphragm are all a part of the respiratory system.


Ribonucleic acid; a type of genetic material. Humans, plants, animals, bacteria and some viruses have both DNA and RNA. In humans, DNA stores the information that says how to code our body, while RNA reads that DNA and helps make the proteins and enzymes that make things happen. Sometimes, the RNA can make things happen on its own, too. Coronavirus is an RNA virus or ribovirus, which means that drugs that treat it need to somehow block the virus’ RNA from invading our cells.


A way to sequence DNA and RNA in near real time. Most tests for coronavirus are RT-PCR tests. These tests have a high rate of false negatives but a low rate of false positives, so most people are tested twice. 



Another coronavirus that caused an outbreak in the mid-2000s. Severe acute respiratory syndrome (SARS) was not as infectious as SARS-CoV-2, but it did have a much higher fatality rate.


The novel coronavirus that was first noticed in Wuhan, China, and is responsible for the current outbreak. The disease it causes is called COVID-19.

secondary infection

A separate, unrelated infection caused by another disease. Bacterial pneumonia is a secondary illness that can be caused by COVID-19.


To refrain from any contact with other individuals for a period of time (such as two weeks) during the outbreak of a contagious disease usually by remaining in one's home and limiting contact with family members. The verb is fairly recent, showing evidence of use only within the past 20 years or so. The noun has been in occasional use prior to this in the 20th century.

serological survey

A survey that looks for immune cells in a person’s blood. Serological tests are a way to tell if someone was once infected with a disease and then got better. 

shelter in place

All residents must remain at their place of residence, except to conduct essential activities, essential businesses, and essential government functions.

situation report

The World Health Organization releases daily situation reports that track the spread of and fight against coronavirus across the world.

social distance

The avoidance of close contact with other people during the outbreak of a contagious disease in order to minimize exposure and reduce the transmission of infection. The practice of maintaining a greater than usual physical distance from other people is referred to as social distancing, in use since 2003; the verb is socially distance. 

stay at home order

A stay at home order directs people to limit movements outside of their homes beyond essential needs. This limits social interactions to help prevent the spread of disease.


Also written as superspreader. An individual who is highly contagious and capable of transmitting a communicable disease to an unusually large number of uninfected individuals. The term for the spread of disease by super-spreaders is super-spreading.

Supplement, nutritional

Drinks that can be used in addition to meals to increase intake of calories and nutrients.

suspected case

A person who may have a disease because of their symptoms and risk factors based on current guidelines. This person either had no test or an inconclusive test.


Theophylline agents

These agents open airways, prevent and relieve airway spasms, and prevent night-time cough and shortness of breath.


A small, hand-held device that helps to keep the airways open and prevent the lungs from collapsing.


The muscular and bony structure of the chest.

tidal volume

The quantity of air inhaled and exhaled in one respiratory cycle during regular breathing.

total lung capacity test

A test that measures the amount of air in the lungs after a person has breathed in as much as possible.


The main airway (windpipe) supplying air to both lungs.


A surgical opening made when necessary in the main airway, the trachea.


The spread of disease. A disease can be transmitted from person to person, from person to animal to person or by the environment (think: giardia in water.) Coronaviruses are transmitted in respiratory droplets, which are drops of water and mucus that come out of our lungs when we cough and sneeze. They can also contaminate door handles and surfaces.



An injected medication that might stimulate the immune response to protect a person from an infection.


A device that delivers air into the lungs through a tube that is placed into the mouth or nose and down into the windpipe. 

viral shedding

The period of time after the virus has replicated in the host and is being emitted.


A measure of how much damage a germ does. Virulence can also refer to chemicals and toxins. COVID-19 is more virulent than the flu but less virulent than SARS and MERS.


A type of germ or microbe. Viruses are not considered alive because they don’t have the tools they need to replicate on their own. The flu, COVID-19, Zika and Ebola are all caused by viruses. Viruses cannot be treated with antibiotics.

vital capacity

Maximal breathing capacity; the amount of air that can be expired after a maximum inspiration



The high-pitched whistling sound of air entering or leaving narrowed airways

World Health Organization

A global organization that directs international health for the United Nations. They study communicable and non-communicable diseases, illnesses caused by environmental factors like pollution and illnesses caused by germs. They are coordinating the global response to COVID-19 and tracking its spread.



Zinc is a mineral that may have antiviral properties. Some studies suggest that zinc can reduce the length and severity of a cold if you take it within the first 24 hours of a disease. But some people have criticized those studies and others haven’t found an association. The Mayo Clinic does not recommend the use of zinc to treat colds, or any other virus.


A disease that infects humans but originally came from other animals. The genetic sequence of the COVID-19 virus is similar to a coronavirus found in bats, so that may be where this disease originated. It may also have passed through other species on the way to humans, like snakes. Some zoonotic diseases, such as Zika and malaria, cannot be passed from person to person without an animal host.

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