The global pandemic has introduced us to new words and phrases. This resource provides a description of some key terms used with the current Coronavirus (COVID-19).

Aerosol and Droplet Transmission
When an infected person coughs or sneezes, there is a spray of large droplets and much smaller droplets released into the air and both can contain the COVID 19 virus.  The larger droplets will be better filtered through a mask, but when a mask is not worn they are likely to fall from the air within six feet of the infected individual in a short period of time.  (This is the reason for 6 ft social distancing and wearing a mask).  Large droplets are believed to be the main way of transmitting COVID 19 virus.  Since aerosol droplets are much smaller and lighter, they can remain suspended in the air for several hours.  It has not been proven aerosols represent a significant way of spread for COVID 19.  The aerosol droplet with virus may be diluted and present a smaller dose which is not able to infect the person breathing in the droplet.  The aerosolized virus may become inactive or unable to infect someone in a short time period.  A great deal of research is being conducted to determine if aerosol transmission plays a significant role in the spread of this coronavirus.

Not showing any symptoms (signs of disease or illness). Some people without any symptoms still have and can spread the coronavirus. They’re asymptomatic, but contagious. Fever, cough, and shortness of breath are the main symptoms of COVID-19.

A collection of cases occurring over a short period of time in one area.  Often these cases are related in some manner. 

Community Spread
Transmission of an infectious agent such as a virus from person to person within the community due to residents having contacts within a variety of community settings.  Early in the pandemic, cases were said to be due to travel because a person did not get infected in the community but while traveling outside the country or state.

Confirmed Cases
Persons who test positive using a COVID 19 PCR (polymerase chain reaction) test.  As of 9/28/2020, this is the most reliable test available.  A person who tests positive using a rapid antigen test is considered a “probable” case and must have a positive follow-up PCR test to be counted a “a confirmed case.”  

Contact Tracing
A proven process for limiting spread of an infectious disease.   The process entails interviewing all confirmed cases of COVID-19; determining all persons with whom they have had contacts during a period when they could have been infectious; interviewing all the contacts named by the infected person; determining the closeness of the contact and potential for transmission of the virus; determining which people should be isolated or quarantine to prevent spread of the virus to other people, (see definitions below), and to provide education to the contacts about the disease and where to find assistance if needed.  

A family of related viruses known for the crown-like spikes on their surfaces. One group of viruses of this family produces the common cold.  Other forms of this family have produced other respiratory illnesses such as SARS (Severe Acute Respiratory Syndrome outbreak in 2002), and MERS (Middle East Respiratory Syndrome outbreak in 2012.  The virus producing the current pandemic is SARS-CoV-2.  

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

Case Fatality Rate (CFR)
An estimate of the risk of mortality from a contagious disease. The CFR is calculated by dividing the number of deaths caused by a disease by the number of cases of that disease in a given time period. The CFR is time and location-dependent, and many different factors can influence the CFR, such as speed of diagnosis of cases, health system capacity, age and other demographic characteristics, among others. For COVID-19, estimates of the CFR have varied; in China, CFR estimates by province have ranged from <1% to 5.8%. (Sources: CDC/Lipsitch et. al./WHO)  

Case Rate
This term applies to how many new cases are occurring per an established number within a population.  It can be used for the daily case rate, the 7-day average case rate, or the case rate since the beginning of the pandemic.  Currently, Maryland is using the case rate per 100,000 people and is reporting the 7-day average of cases as the daily case rate per 100,000 people.  For example, if over the past seven days the cases for Talbot County were 3, 5, 0, 2, 7, 3, and 4 = 24, the average would be 3.42 or the average number of cases per day for our 37,250 population.  Divide 100,000 by 37,250 and you get 2.68.  Now, multiply 2.68 X 3.42 and you get the case rate per 100,000 for Talbot County.  This may seem complicated but it is the only way to compare counties and countries because populations vary so greatly. 

Flattening the Curve
What it means during coronavirus: “You want to spread out the rate of infection so as to not overwhelm our health care system and infrastructure. If everyone is out and about, it’s more likely that everyone will get sick at once. But if you’re able to spread out how many people get sick, over time, patients can get the treatment they need because hospitals and other resources will not be exhausted.” 

Herd Immunity
When the majority of people in an area are immune to a specific infection, even the members of the population (herd) are protected simply by being around them. Anywhere from 50% to 90% of the population would have to have antibodies to COVID-19 in order for herd immunity to kick in.


Incubation Period
The time between when a person is infected by a virus and when he or she notices symptoms of the disease. Estimates of the incubation period for COVID-19 range from 2-14 days, but usually is between 2 and 5 days.


On a larger scale, isolation involves keeping people with confirmed cases of a contagious disease separated from people who are not sick. If you have a confirmed case of COVID-19, for example, you may be put into isolation for public health purposes—it may be voluntary or compelled by federal, state, or local public health orders.  The time period depends upon when symptoms first started and how rapidly symptoms improve.


A sudden increase or cluster of cases of a specific illness in a limited area or a facility. 


Epidemic is the sudden, wide spread of a disease above what is usually expected.


Pandemic is when a disease spreads beyond national borders into other countries worldwide.  An outbreak of severe pneumonia was noted in Wuhan, China related to a seafood market. As it spread rapidly in China it became an epidemic. As it spread to countries around the world, it became a pandemic. 


PCR Test
This COVID-19 test detects genetic material of the virus using a lab technique called polymerase chain reaction (PCR). Also called a molecular test, a health care worker collects fluid from a nasal or throat swab or from saliva. PCR tests are very accurate when properly performed by a health care professional, but the rapid test can miss some cases.


Personal protective equipment (PPE)
Specialized clothing or equipment, worn for protection against infectious materials. 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.


Positivity Rate or Percent of Tests Positive
There are two ways to calculate positivity rate:

Method 1: Divide (A) the number of people who have tested positive by (B) the number of people who have been tested.
This method is used by Johns Hopkins and considered a more accurate picture of what is happening because duplicate tests for the same individuals are removedIt is not unusual for this to show a higher positivity rate than the method below.  

Method 2: Divide (C) the number of positive tests by (D) the number of total tests. This method is used by Maryland Department of Health and does not remove duplicate tests on individuals during the time period. 

With either method, a high volume of tests tends to lower the positivity rate. 


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.


Rapid Antigen Test
This COVID-19 test detects certain proteins in the virus. Using a nasal or throat swab to get a fluid sample, antigen tests can produce results in minutes. Because these tests are faster and less expensive than PCR tests, antigen tests may be more practical to use for large numbers of people. A positive antigen test result is considered very accurate, but there’s an increased chance of false-negative results — meaning it’s possible to be infected with the virus but have a negative result. Depending on the situation, the doctor may recommend a PCR test to confirm a negative antigen test result.


This is not the same as a coronavirus test. This step helps healthcare 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.


A voluntary agreement, this means you are to remain at home and not go to work or school. You’ll be expected to limit your movements outside and monitor your health for 14 days after returning from travel to or arriving from a place known to have high numbers of COVID-19 infections.


Self-quarantining is designed to restrict the movement of healthy people who may have been exposed to someone who has tested positive for COVID-19. The CDC suggests staying at home for 14 days from the exposure. 


Serology Test
Also called an antibody test, this checks to see if you have antibodies in your bloodstream that indicate you had been infected with the virus in the past.


Shelter in Place
A decree, usually from a government official, for people to stay in their homes with exceptions that include going out for essential needs, such as groceries, as well as outdoor activities like walking and biking in public spaces. People who work in critical services, like health care or law enforcement, or essential businesses, are usually excluded from these mandates.


Social Distancing
Maintaining a distance of approximately 6 feet from others to stop or slow the spread of COVID-19.


When a person shows signs of illness. For COVID-19, that includes cough, fever or shortness of breath.


Viral Load
Also called viral dose, viral load refers to the amount of virus you are exposed to. Someone who is exposed to a relatively small amount of the coronavirus might not get any symptoms, while someone who is exposed to a large amount is more apt to get severe symptoms.







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