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Coronavirus (COVID-19 [2019-nCoV], SARS, MERS)

Reviewed on 4/29/2020

What Facts Should You Know About Coronaviruses?

Coronaviruses include the Wuhan coronavirus (2019-nCoV), SARS, and MERS, among others.
Coronaviruses include COVID-19 (Wuhan coronavirus, 2019-nCoV), SARS, and MERS, among others.
  • Coronaviruses are very common. Most coronaviruses that infect humans cause mild symptoms like a common cold and go away on their own. Very few may cause severe disease such as viral pneumonia that may lead to death.
  • Coronaviruses spread easily from person to person by inhalation of respiratory secretions or by contact of respiratory secretions with the eyes, nose, or mouth. Rarely, fecal contamination can transmit COVID-19.
  • Frequent cleansing of hands with soap and water or alcohol-based sanitizers and avoiding crowds can help prevent infection with coronavirus, influenza, and many other upper respiratory infections. Experts also recommend that people cough or sneeze into their elbow or cover their mouth and nose with a tissue that they can throw away.
  • Coronaviruses also infect animals. Some strains can also infect humans or evolve the ability to spread to humans.
  • There are 7 known coronaviruses that infect people, including the newly discovered 2019 novel coronavirus (COVID-19 or 2019-nCoV, also known as Wuhan coronavirus), Middle East respiratory syndrome coronavirus (MERS-CoV), and severe acute respiratory syndrome coronavirus (SARS-CoV).
  • MERS-CoV, SARS-CoV, and COVID-19 (Wuhan coronavirus, 2019-nCoV) made the news in recent years because they evolved and have the ability to spread from animals to humans and because they caused deaths.
  • Researchers believe that MERS-CoV spread from camels in Saudi Arabia in 2012.
  • Researchers believe that SARS-CoV spread from bats and civet cats in China in 2002.
  • It is believed that an animal source of COVID-19 (Wuhan coronavirus, 2019-nCoV) first infected humans at a market that sells live animals for food in Wuhan, Hubei Province, China, in 2019.

What Is a Coronavirus?

Coronaviruses belong to the Coronaviridae family of viruses and are named for the crown of spikes on their surface. There are four known subgroups: alpha, beta, gamma, and delta coronaviruses. There are very many coronaviruses in nature, and they infect a variety of animals, humans, or both. Researchers have detected over 70 coronavirus species in bats alone in China. Researchers first recognized coronaviruses that infect humans in the 1960s. They generally spread in respiratory secretions between animals, animals to people, or person to person. New coronaviruses may occasionally spread from animals to cause infections in humans. This happened with MERS-CoV (from camels) and SARS-CoV (possibly bats or civet cats).

To date, seven coronaviruses that infect people are known:

  1. 229E (alpha coronavirus)
  2. NL63 (alpha coronavirus)
  3. OC43 (beta coronavirus)
  4. HKU1 (beta coronavirus)
  5. MERS-CoV (a beta coronavirus that causes Middle East respiratory syndrome, or MERS)
  6. SARS-CoV (a beta coronavirus that causes severe acute respiratory syndrome, or SARS)
  7. 2019 novel coronavirus (2019-nCoV), COVID-19, or Wuhan coronavirus (a beta coronavirus similar to SARS-CoV)

Most human infections occur with the first four coronaviruses listed. They commonly cause "common cold" symptoms and do not cause deaths. Researchers believe the last three only recently evolved to infect humans and have caused outbreaks associated with deaths. It is possible that they may cause more severe disease because they are new coronaviruses that most human immune systems do not have prior antibodies to and are unaccustomed to. Most domestic pets such as dogs and cats are not known to spread serious coronavirus infections to humans. However, animals raised for food and sold at live animal markets have spread coronaviruses such as SARS-CoV, MERS-CoV, and probably Wuhan coronavirus (2019-nCoV).

In 2012, researchers first identified MERS-CoV in humans and traced it to markets and livestock farms in Saudi Arabia, where people raise camels for milk and meat. Outbreaks, including spread to other countries, have originated in the Arabian Peninsula. About 3-4 out of 10 infected people have died from it. In 2002, researchers first identified SARS-CoV in Guangdong Province in southern China. It caused a global outbreak that ended in July 2003. Researchers suspect an animal source, possibly bats or civet cats, from a live animal food market. Smaller incidents occurred afterward, three being from laboratory accidents. 2019-nCoV appeared in Wuhan, Hubei Province, China, and spread rapidly. Based on early information, it appears to have originated from an animal and seafood market. Investigation is yielding new information daily and is updated at CDC, 2019 Novel Coronavirus.

What Are the Risk Factors for a Coronavirus Infection?

Risk and complications vary according to the species of coronavirus. The main risk factor for a coronavirus infection is exposure to the respiratory secretions of an animal or person infected with a strain that can infect humans. Coronaviruses are thus most easily spread when there is crowding and frequent contact of surfaces by many people or frequent contact with saliva and respiratory secretions. For example, child care centers and schools are often sources of upper respiratory virus infections such as coronaviruses. Workplaces, public transit, and shopping centers pose risks during an outbreak. Cold weather brings more groups and public crowding indoors and increases the risk of cold viruses like coronavirus, among many other respiratory viruses. Thus, they often peak during winter and spring.

Risk factors for COVID-19 (Wuhan coronavirus, 2019-nCoV) include the following:

  • Having close contact with someone who has recently visited Wuhan, China (Avoid travel to Wuhan, China, until the CDC or World Health Organization changes the travel status.)
  • Coming in contact with secretions and feces from an infected person
  • Eating or handling wild animals native to China

MERS-CoV is not currently circulating. Risk factors for MERS-CoV generally include exposure to

  • a sick traveler returning from the Arabian Peninsula;
  • camels, camel markets, or camel meat or dairy products; and
  • travel in the Arabian Peninsula or other area, especially if involved during a known outbreak of MERS-CoV.

There are no specific risk factors for SARS-CoV at this time because it is not known to be circulating. Because most coronavirus are mild and self-limited and patients with symptoms are not expected to cause outbreaks, health care workers have been at risk for severe coronavirus and some have died. This has happened especially early during an outbreak when infection prevention measures have not yet been established.

What Is the Incubation Period for a Coronavirus Infection?

The incubation period (the time from infection to development of symptoms) for coronaviruses varies by species. Most common cold coronaviruses cause symptoms within 2 days, but again this may vary. For example, the incubation period for COVID-19 (Wuhan coronavirus, 2019-nCoV), MERS-CoV, and SARS-CoV seems to be anywhere from 2-14 days.

What Are the Signs and Symptoms of a Coronavirus Infection?

Most people have had one or more coronavirus infections and were unaware that they had a coronavirus. Most coronavirus infections, as with many respiratory viruses that circulate throughout the year, cause a self-limited cold for a few days, with typical signs and symptoms of

Often, there is no or very mild, brief fever. Symptoms resolve within a few days to a week without lasting aftereffects in mild infections.

Rarely with specific species of coronavirus (like MERS-CoV, SARS-CoV, and COVID-19 [Wuhan coronavirus, 2019-nCoV]) do coronaviruses cause additional symptoms. These viruses may cause shortness of breath or difficulty breathing if the illness progresses to viral pneumonia or lung inflammation. With more severe infection, the viral pneumonia may cause respiratory failure (severe acute respiratory syndrome) and require mechanical ventilation support. In addition, severe infection may cause kidney failure (requiring hemodialysis), and systemic inflammatory syndrome that leads to shock and death. Depending on the coronavirus, other signs and symptoms might include

  • headaches,
  • muscle pain,
  • chills,
  • body aches,
  • nausea,
  • vomiting,
  • loss of sense of smell (anosmia),
  • repeated bouts of shaking chills,
  • loss of sense of taste (ageusia), and
  • diarrhea.

How Does a Coronavirus Spread?

Coronavirus spreads the way most cold viruses do. How it spreads is through respiratory droplet secretions containing coronavirus that come into contact with the eyes, nose, or mouth, either from breathing them in after someone coughs or sneezes, or from being rubbed into these areas by hands after touching secretions on a contaminated surface. COVID-19 also spreads via fecal contamination. Crowds and public places increase the opportunities for infection. Being in enclosed spaces with a lot of individuals increases exposure as well.

How Contagious Is a Coronavirus?

Most coronaviruses are as contagious as common cold viruses or influenza virus (the flu virus). In other words, they can be very contagious from person to person but not as contagious as measles. For example, direct contact of hands with secretions or breathing within 3 feet of a cough or sneeze is required, not simply walking by a sick person. People with SARS should avoid public places for 10 days after illness. It is not clear for how long MERS is contagious, but it is likely similar. Most close contacts of people with MERS have not become ill. COVID-19 seems more contagious than SARS or MERS.

What Are Treatments for Coronavirus Infections?

There are very limited treatments for coronavirus infections other than supportive treatment of symptoms such as fever, congestion, and discomfort. Common cold remedies such as over-the-counter medicines help improve comfort while the infection runs its course. There is no antiviral treatment for most coronavirus infections. Severe coronavirus infections may require hospitalization and intensive care support such as mechanical ventilation and blood pressure support. A new antiviral drug (remdesivir, also known as GS-5734) under investigation for treating Ebola virus has also been found to be effective against MERS-CoV and SARS-CoV, but it is still in development and not commercially available. There is no drug to treat COVID-19.

What Are Potential Complications of Coronavirus Infections?

Complications of coronavirus are very rare except in the case of immune deficiency or a strain of coronavirus known to cause severe infection, like MERS-CoV, SARS-CoV, or COVID-19 (Wuhan coronavirus, 2019-nCoV). Complications include viral pneumonia, which may lead to severe acute respiratory failure. In addition, widespread inflammation (sepsis, or systemic inflammatory response syndrome or SIRS) may lead to shock, kidney failure, and even death in some cases.

Is It Possible to Prevent a Coronavirus Infection? Is There a Coronavirus Vaccine?

Yes. The best way to prevent coronavirus and other respiratory viruses that often circulate at the same time is to avoid inhaling infectious respiratory secretions or touching surfaces that may be contaminated.

  • Limit being in public or crowded places during winter and spring or when an outbreak of respiratory viruses is suspected.
  • Stay home if you are sick with cold symptoms.
  • If you must be around other people, cover your cough or sneeze with your elbow or sleeve to avoid contaminating your hands and then contaminating objects you touch. You can also use tissues that you can throw away.
  • Wash hands frequently with soap and water.
  • Use alcohol-based hand sanitizer often, especially if frequently touching potentially contaminated surfaces (for example, public keyboards, touch pads, doorknobs, elevator buttons).
  • Surgical masks are of limited value in preventing transmission or infection with most respiratory viruses, especially if they are worn a long time and become moist from breath. Masks do not replace the respiratory and hand hygiene measures above.
  • Health care workers should pay close attention to public health guidance about severe respiratory virus outbreaks to reduce their risk of infection. For MERS, SARS, and COVID-19, people usually use barriers such as gloves, gowns, and masks during a hospital stay.

There is no vaccine for coronaviruses at this time.

What Is the Survival Rate for Coronavirus Infections?

Almost all human coronavirus infections are self-limited and go away within a few days without specific treatment. Thus, survival rates are typically excellent except for a very few coronaviruses.

MERS-CoV: The case fatality rate is about 30%-35%.

SARS-CoV: The case fatality rate has ranged from 7%-50%, with older patients having the highest mortality.

COVID-19 (Wuhan coronavirus, 2019-nCoV): Information is evolving (current estimates of a case fatality rate -- about 6.95%). Updates are available at CDC.

Health Solutions From Our Sponsors

Reviewed on 4/29/2020
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Monaghan, K.J. "SARS: DOWN BUT STILL A THREAT." In: Institute of Medicine (US) Forum on Microbial Threats. Knobler S, Mahmoud A, Lemon S, et al., editors. "Learning from SARS: Preparing for the Next Disease Outbreak: Workshop Summary." Washington (DC): National Academies Press (US), 2004.

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