A newly identified respiratory virus that causes pneumonia was recently discovered in China.
Cases of the virus, a type of coronavirus called COVID-19, have spread in China, and have also been reported in more than 20 other countries, including the United States.
Here's what to know about the coronavirus.
What is a coronavirus?
Coronaviruses are a group of viruses that can cause a range of symptoms including a runny nose, cough, sore throat and fever. Some are mild, such as the common cold, while others are more likely to lead to pneumonia. They're usually spread through direct contact with an infected person.
The coronavirus gets its name from the crown-like spikes on its surface, according to the CDC. (Corona is Latin for crown.) Including the newly identified form of the virus, there are a total of seven coronaviruses that can infect humans, the CDC says. Other well-known coronaviruses include SARS and MERS.
The new virus is called COVID-19. It's unclear how easily it spreads from person to person, but the CDC recommends that anyone who may have been exposed to the illness monitor themselves for 14 days after close contact with an infected person.
Symptoms to watch for include fever, cough, shortness of breath, trouble breathing, body aches, sore throat or vomiting and diarrhea.
How does the new coronavirus spread?
Researchers are still learning precisely how the new virus spreads from person to person.
"While we do not know all of the mechanisms of spread of the epidemic so far, there is likely spread by droplets and contaminated surfaces, and possible airborne [spread], similar to SARS," Dr. Mark Denison, a virologist at the Vanderbilt University Medical Center, said.
Coronaviruses in general are spread through close contact — a range of about 3 to 6 feet. The virus is primarily spread through a sick person coughing or sneezing on someone, said Dr. Kathy Lofy, a health officer in Washington state.
A person could also become infected through contact with the virus particles on a surface, though it's unknown how long the new coronavirus can survive on surfaces outside of the body. If an infected person sneezes or coughs onto a surface, such as a countertop or doorknob, and another person touches that surface and then rubs his or her eyes or nose, for example, the latter may get sick.
The SARS virus was also spread through feces. Denison suggested the same spreading mechanism may be found in the new virus, but it's too early to know for sure.
Can coronavirus be spread through the mail or through goods imported from China?
It’s extremely unlikely. While more needs to be learned about how this particular virus works, coronaviruses typically don't live very long on surfaces, and are very unlikely to survive over a period of days or weeks when an item is being shipped.
"There is no evidence to support transmission of [COVID-19] associated with imported goods and there have not been any cases of [COVID-19] in the United States associated with imported goods," said Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, during a call with journalists.
Is the coronavirus likely to spread in areas in the U.S. with confirmed cases?
So far, none of the confirmed coronavirus patients in the U.S. has infected anyone else in this country. Dozens of their close contacts are being closely monitored for at least 14 days, with daily checks for fever and cough. Health officials continue to believe the risk for sustained human-to-human transmission from these cases is quite low.
A bigger viral risk in those cities (and everywhere else in the country) is the flu. The CDC estimates there have been 15 million flu cases so far this season nationwide, with 210,000 hospitalizations and 12,000 flu deaths, including 78 children, as of Feb. 1.
"Our influenza problem is large," Dr. William Schaffner, an infectious disease specialist at Vanderbilt University, told NBC News. "Our coronavirus problem — very small and so far contained."
How long does it take for someone to get sick?
The new coronavirus's incubation period — meaning the time it takes from a person being infected with the virus to when they start showing symptoms — is still unknown.
However, public health experts are working under the assumption that the incubation period is about 14 days. It's unclear whether a person is contagious during the incubation period.
Does a face mask protect you from coronavirus?
The CDC recommends that patients with the coronavirus wear a face mask to protect others around them, or, if the patient cannot wear a face mask, others should if they are in the same room together.
Caregivers or people living in the same house as someone who is sick should also wear disposable face masks, along with gloves and disposable gowns, when coming into contact with the patient's bodily fluids.
For health care workers in contact with coronavirus patients, the CDC recommends a more specialized type of mask — one that is individually fitted to a person's face to create a seal and that filters out 95 percent of particles that at least 0.3 microns in diameters. (A micron is 1/1,000th of a millimeter.) This type of mask is called N95.
At this time, the size of the coronavirus particles is unknown. The SARS virus was 0.1 microns in diameter.
How can I prevent coronavirus?
One of the simplest prevention measures a person can take is proper hand-washing.
The CDC recommends washing hands with soap and water before eating, after using the bathroom, and after blowing your nose, coughing or sneezing, and before and after caring for a sick friend or a family member.
The most effective way to clean hands is to wet them with clean water, then apply soap and scrub for at least 20 seconds, before rinsing and drying with a clean towel.
Is it SARS?
No. SARS, or severe acute respiratory syndrome, is a type of coronavirus that was first reported in Asia in February, 2003.
Over the following months, the illness spread to more than two dozen countries, sickening 8,098 people worldwide, killing 774.
However, COVID-19 is a different strain. It's unknown at this point if the new virus is as severe or as contagious as SARS. While some patients in China have had serious illness, other patients have had milder illness and been discharged.
Is there a coronavirus vaccine?
There is no specific treatment for the new virus, and no vaccine to prevent it. The National Institutes of Health confirmed Tuesday it's in the "very preliminary stages" of research to develop a vaccine, but declined to provide details.
In addition, the drug company Regeneron is in the early stages of work on a potential treatment for this coronavirus. The company previously developed a similar treatment for Ebola.
Do disinfectants kill the coronavirus?
Yes, they can. The CDC suggests that anyone exposed to an infected patient clean all "high-touch" surfaces, such as counters, tabletops, doorknobs, bathroom fixtures, toilets, phones, keyboards, tablets and bedside tables.
Cleaning agents can include a household disinfectant with a label that says "EPA-approved," according to the CDC. A homemade version can be made, using one tablespoon of bleach to one quart of water.
Follow NBC HEALTH on Twitter & Facebook.
