COVID-19 Glossary

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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.

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