A newly identified respiratory virus that causes pneumonia was recently discovered in China.
Cases of the virus, a type of coronavirus, have spread in China, and have also been reported in nearby countries in Asia and in the United States and France. The number of confirmed cases has soared to nearly 2,000 and there have been at least 56 deaths.
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, the deadly MERS and milder ones such as the common cold.
The new virus is called 2019-nCoV. 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.
"It is likely there will be more cases reported in the U.S. in the coming days and weeks, likely including person-to-person spread," the CDC said in a statement on Jan. 26.
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.
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 are 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?
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, 2019-nCoV 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.
What's the risk this will spread in the U.S.?
CDC officials maintain that the likelihood this coronavirus will spread from person to person in the U.S. is low. However, isolated cases from travelers are likely. The first case in the U.S. was reported by CDC officials on Jan. 21: a male in his 30s who traveled from Wuhan. A second case, a woman in her 60s in Illinois, was reported on Jan. 24. On Jan. 26, the CDC said the number of confirmed cases of the new coronavirus in the U.S. has risen to five. About 100 samples from 26 states have been sent to the CDC for testing and more are expected.
There is no evidence that person-to-person transmission has occurred anywhere in the U.S., although health officials are monitoring close contacts of all patients closely.
Passengers traveling from China are being screened at major airports, including New York's JFK airport, San Francisco, Los Angeles, Hartsfield-Jackson Atlanta International Airport and Chicago's O'Hare International Airport.