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Living through the COVID-19 pandemic means dealing with a new and sometimes confusing vocabulary. Here's a guide to some of the most common words and phrases you might come across.

Not having signs of illness (symptoms). People who are asymptomatic can still be infected with COVID-19 and can spread the virus to others.

The number of deaths divided by the total number of known cases of a disease. For example, if 100 people in a community are diagnosed with COVID-19 and two of them die, the case fatality rate is 2/100, or 2%.

It's important to keep in mind that the CFR often overestimates the actual mortality (death) rate, and can make a disease seem more deadly than it is. That’s because some people never get diagnosed, so we don't always have an accurate count of the cases.

You generally need to be in close contact with a person that has COVID-19 to get infected. Close contact includes:

  • Living in the same household as a person with COVID-19
  • Caring for a person with COVID-19
  • Being within 6 feet of a person with COVID-19 for a combined total of 15 minutes or more within a 24-hour period, OR
  • Being in direct contact with saliva or other body secretions from a person with COVID-19 (e.g., being coughed on, kissing, sharing utensils, etc.).

Any of these activities for any duration may put someone at greater risk of contracting COVID-19 from someone who is infected. Previously, the CDC had defined prolonged close contact as a time period of 10 or more minutes. This definition has been extended to 15 or more minutes, which aligns with the time period used in the CDC’s guidance for contact tracing.

A collection of cases happening in the same place around the same time, above what is normal. For example, you might see a cluster of cases in a long-term care facility, a workplace, or among people who attended a party.

When a contagious disease is spreading in a community but we don’t know how or where every infected person got exposed.

A person (with or without symptoms) who received a positive result from a COVID-19 laboratory test.

Identifying all the people who may have been in close contact with an infected person while they were contagious.

A family of viruses. Some coronaviruses cause the common cold, and others cause serious health issues, like pneumonia. Coronaviruses start in animals, like camels, civets and bats. Most of the time, people can’t catch coronavirus. But once in a while, a coronavirus can spread from animals to people and then from person to person.

A shorthand for "coronavirus disease 2019."

An increase in the number of cases of a disease in a population, above what is normal. Epidemics often happen suddenly. COVID-19 began as an epidemic in China.

The study of the spread or pattern of sickness in a group of people.

When a person comes into contact with a germ that causes disease. For example, a doctor might get exposed to COVID-19 while caring for an infected patient.

Slowing the spread of a disease so that you don’t overwhelm the healthcare system. The “curve” represents the number of cases over time. When you flatten the curve, you prevent a big spike of new cases in a short period of time. Instead, you’ll probably see the same number of cases spread out over a longer period of time.

Washing hands with clean, running water and soap for at least 20 seconds. Or using hand sanitizer that contains at least 60% alcohol. Hand hygiene is a key strategy for slowing the spread of COVID-19 and many other diseases.

Certain groups of people who are more likely to get seriously ill from COVID-19. People over 60, people with underlying health issues, and pregnant people may be at higher risk.

Protection from disease. If you have immunity to a disease, you won’t get sick from it.

Having a reduced ability to fight infections and other diseases. People can be immunocompromised because of certain conditions, like AIDS, cancer, and diabetes, or because of certain medications and treatments, like chemotherapy. People who are immunocompromised may be more likely to get very sick from COVID-19.

The time between when a person first gets exposed to a germ and when they develop symptoms. For COVID-19, the incubation period ranges from 2 to 14 days.

A coronavirus strain that we haven't seen before. COVID-19 is novel because it is a new respiratory virus that was first identified in Wuhan, China in December 2019. Health experts are concerned because this new virus can cause severe illness and death in some people.

Same definition as epidemic, but used for a smaller geographic area. For example, King County’s COVID-19 outbreak began in late February.

An epidemic that has spread over several countries or continents. Pandemics usually affect a large number of people. It’s important to remember that the word pandemic is mostly about how much a disease has spread, not how dangerous the disease is. COVID-19 is now a pandemic because many countries throughout the world have cases.

Special clothing or equipment to protect people from infection. PPE can include gloves, gowns, aprons, masks, respirators, goggles, and face shields. It’s especially important for healthcare providers and emergency responders to have PPE.

An infection of the lungs that can make it harder to breath. Pneumonia can range from mild to life-threatening.

Also called the R0, pronounced "R naught": A mathematical term that can indicate how quickly a disease is spreading. R0 tells you the average number of susceptible (unvaccinated, not protected) people who will catch a disease from one contagious person. If the R0 is 2, then on average, every case will create two new cases.

It's important to remember that the R0 can change over time and place. It depends on a lot of different factors, like environmental conditions and people's behaviors. For example, when people practice social distancing, the R0 may decrease.

The spray made when a person sneezes, coughs, or even talks. In general, respiratory droplets can travel up to six feet before dropping to the ground or a nearby surface.

An illness that affects the parts of the body involved with breathing, like the nose, throat, and lungs.

The specific coronavirus that causes COVID-19 disease.

A health check to see whether a person has a disease. You can screen by taking a person’s temperature and asking questions about symptoms.

Staying home and away from others while you are ill. If you have COVID-19 symptoms or a positive test, you should self-isolate. Your isolation can end when:

  • Your symptoms get a lot better AND
  • You have had no fever for at least 72 hours without the use of medicine AND
  • At least 7 days have passed since your symptoms started.

Checking yourself for symptoms. This includes regularly checking your temperature (typically, twice a day) and watching for signs of a respiratory illness, like fever, cough, or shortness of breath.

Staying home and away from others when you are feeling well but are watching for symptoms. Health experts recommend you self-quarantine for 14 days when you’ve been in close contact with someone that has COVID-19. During those 14 days, you should self-monitor for symptoms and call your healthcare provider if you develop fever, cough, or shortness of breath.

Increasing the physical space between people to avoid spreading illness. Right now, we can practice social distancing by staying home as much as possible and keeping at least six feet away from other people when we need to go out.

Collecting, analyzing, and interpreting health-related data. Surveillance helps public health professionals plan, carry out, and evaluate their work.

A person that shows symptoms of COVID-19 but either has not been tested or is waiting for test results. If test results are positive, a suspected case becomes a confirmed case.

Having signs of illness (symptoms). The most common COVID-19 symptoms are fever, cough, and shortness of breath.

How a disease moves around, or spreads. Diseases can be transmitted in a few different ways. Some of these include:

  • Direct contact: when a disease spreads through skin-to-skin contact, kissing, and sexual intercourse.

  • Droplet transmission: when a disease spreads by traveling on droplets of fluid, like saliva and mucus. When an infected person coughs, sneezes, or even just talks, droplets can land in the mouths, noses, or eyes of people who are nearby. People can also breathe the droplets into their lungs. Droplet transmission can also happen when a person touches something that has infected droplets on it, and then touches their face. Droplet transmission is the most common way COVID-19 spreads.

  • Airborne transmission: when germs are carried by dust or tiny droplets (called "droplet nuclei") that hang in the air. Unlike droplets that fall to the ground within a few feet, droplet nuclei can hang in the air for long periods of time and can be blown over long distances. It's possible that COVID-19 can be airborne, especially in certain settings like hospitals where special equipment may be used. But scientists don't currently think this is the main way COVID-19 spreads.

A machine that helps patients breath when their lungs aren’t working well and they can’t get enough oxygen on their own.

A disease that spreads between animals and people. Common examples include rabies, Lyme disease, and West Nile virus.