There is a lot of controversy among scientists about this definition, hence the public health debate about how SARS-CoV-2, the virus that causes COVID-19, spreads. Generally, what is meant is spread of a contagious disease from a respiratory droplet that is small enough to float in the air or spread farther than 6 feet. The spread of these droplets may be affected by humidity, air flow, and temperature, but more research in this area needs to be conducted. What isn’t clear is if these small droplets contain enough virus to cause someone else to become infected.
A healthy person who is infected by a pathogen and showing no symptoms of disease. People can become infected with a pathogen and experience no symptoms. That person then can transmit, or “carry” the pathogen to another person, infecting them. That person may then become sick, even if the original carrier does not.
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 factors can influence the rate, like age and demographic characteristics, among others. For COVID-19, CFR estimates vary; in China, early CFR estimates by province have ranged from
Coronaviruses are a family of viruses, which cause respiratory illness in humans. It gets its name from the crown-like halo (or corona) surrounding the virus and can be seen under an electron microscope. Scientists have long identified coronaviruses circulating among animals, such as camels, cats and bats. Still, only a few have jumped to people – a spread that is defined by epidemiologists as “zoonotic.”
Before 2020, six coronaviruses were known to be circulating among people, four of which cause about 25 percent of colds. Two others were known to cause extreme illness – Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). SARS and MERS spread between humans via respiratory droplets with close contacts, the way influenza and other respiratory pathogens have spread, but they don’t spread easily and could be controlled. Around 8,000 people worldwide were infected with SARS and approximately 800 died and MERS infected 2,500 and killed about 860. There has been no known community spread of SARS since 2003 and very little community spread of MERS. In January 2020, China announced the emergence SARS-CoV-2019, the virus that causes COVID-19. The genetic sequence of the coronavirus causing COVID-19 shares some of the same genes as SARS. That is how SARS-CoV-2019 got its name. The “2019” designation was given because the virus is known to have begun circulating at some point late in 2019.
A form of contagious disease spread that involves the spray of saliva or respiratory droplets, expelled when an infected person breathes, coughs, sneezes, talks or sings. If someone is nearby, they could breathe in these droplets and become infected. A person could also touch an item where the infected person’s droplets fell and then become infected when they touch their eyes or mouth. Most droplets are large enough that once they are expelled, they drop to the ground, within the range of about six feet. This is why public health officials ask people to keep six feet apart from others in public and to wash their hands.
Infection-to-fatality rate (IFR)
An epidemiology term that quantifies the chances that a person who contracts an infection from a pathogen, will die from it. Not everyone who is infected by a pathogen will show symptoms of a disease. Not everyone who is infected by a pathogen will die. Knowing the IFR helps scientists determine the danger of a particular pathogen and develop countermeasures to prevent its transmission. With novel pathogens, like with the virus that causes COVID-19, this rate is initially difficult to determine because people who aren’t sick aren’t being tested for infection. As time goes on, and more people are tested for the virus, epidemiologists can determine a more accurate figure for the mortality rate of a pathogen.
Infectious diseases spread when a healthy person comes in contact with a pathogen expelled by someone sick, such as through a cough, sneeze, sexual activity, or contact with fecal material. The amount of that pathogen necessary to make that healthy person sick is the infectious dose. With SARS-CoV-2, the virus that causes COVID-19, the infectious dose is unknown, but because no one has immunity to it, researchers suspect the dose is low.
This policy involves separating people known or suspected to be infected with a contagious disease from those who are not sick to prevent them from transmitting disease to others. The definition of “suspected” is based on whether the person is showing symptoms of a contagious disease or whether they met certain laboratory criteria demonstrating they have likely been infected.
A term for an individual who is experiencing long-term health effects from COVID-19, the disease caused by the SARS-CoV-2 virus. While most people recover and return to normal health within days or a few weeks after infection, some people have symptoms that can last for months. Even those who weren’t hospitalized and seemed to initially have mild symptoms, can have symptoms that persist. The symptoms include shortness of breath, extreme fatigue and brain fog. Some even experience serious consequences like inflammation of the heart and loss of lung function. Because the disease is so new, public health officials and scientists are still studying why some infected individuals have symptoms that last longer than others.
Multisystem inflammatory syndrome (MIS-C)
This is a rare and potentially life-threatening inflammatory response associated with COVID-19, the respiratory disease caused by the SARS-Cov-2 virus. The syndrome affects mainly children, and emerges weeks after they have contracted the virus. By the end of May 2020, around 300 children had developed MIS in North America and Europe.
All viruses, including coronaviruses, replicate by attaching themselves to a living cell and subvert the cell’s DNA (the blueprint that directs its function) to reproduce the virus instead. As the virus copies itself, there are naturally errors, or mutations. This is called antigenic drift and shift.
This is a term used by the Centers for Disease Control and Prevention related to the diagnostic testing process for a disease. A presumptive positive result is when a patient has tested positive by a state or local public health laboratory to infection by a pathogen, but has yet to have been confirmed by the CDC. Public health laboratories are a network of specialized governmental health laboratories that operate at the state and local level across the country. Every state and the District of Columbia, has a public health lab and many states have local public labs in metropolitan areas and smaller communities. They are among the keys to public health surveillance and work closely with the CDC and other federal agencies, as well as international health agencies.
The percent of COVID-19 tests with positive results over a seven to 14-day period. As part of public health measures aimed at reducing spread of COVID-19, the World Health Organization recommends that communities aim for a positivity rate of less than 5 percent for at least two weeks . A threshold of 5 percent or more is as an indication that the spread of COVID-19 is not under control in the community.
Involves health authority separating and restricting the movement of people who have potentially been exposed to a contagious disease, until it can be determined whether they have become sick or no longer pose a risk to others. For example, those suspected of exposure to Ebola were quarantined up to 21 days. Quarantines may take place in the home, or other locations determined by health authorities. If a person shows no symptoms of the disease within the time when a person is considered contagious, they are considered disease-free and released from quarantine.
A class of vaccines that utilize a piece of genetic information from a specific pathogen to produce an immune response in the body and prevent disease.
A blood test to detect the presence of antibodies against a microorganism. Antibodies are proteins that the body creates when it detects a foreign presence, such as bacteria or virus.
A serologic test can determine whether a person has been exposed to a particular microorganism, and the potential that they are immune to a disease.
Symptomatic case-fatality rate (sCFR)
An epidemiology term that quantifies the risk that a person who is infected with a pathogen, and showing signs of illness, will die. Knowing this figure helps scientists determine the danger of a particular pathogen. With a fast moving and novel pathogen, like the virus that causes COVID-19, this figure may be a moving target, because only those with illness are tested. As time goes on, and more people are tested for the virus, epidemiologists can determine a more accurate figure for the mortality rate of a pathogen. That is why journalists may want to caveat the mortality rate figures early in an outbreak with something to the effect of: "a mortality rate, based on the information that scientists have."
This is the measure of virus particles. Generally, it refers to the amount of virus present in the body, once a person has become infected and the virus has replicated in the person’s cells. For most people, the higher the viral load, the worse the symptoms and outcomes.
A zoonotic disease refers to a pathogen that has been living within an animal, and then, for an environmental or genetic reason, jumps into the human population where it can cause disease. Two of the best known zoonotic diseases are influenza and the plague. The flu virus lives in the guts of water fowl. The flu can spread to humans through a genetic shift that causes people to become ill. The plague is caused by the bacteria, Yersinia pestis. It can live inside fleas, which then bite humans and cause illness. In 1346, rats carrying fleas with Yersinia pestis, traveled through trade routes in western Europe, causing a pandemic known as the Black Death. Around 60% to 75% of all new diseases that affect humans are zoonotic in origin.