Everything You Need to Know About Coronavirus Transmission

The novel coronavirus, aka COVID-19, is getting close to home. For the first time, health officials have confirmed a case of coronavirus transmission in the U.S. wherein the origin of the virus is unknown.

Previous cases of coronavirus in the U.S. have involved people who had either recently traveled to and from China (where coronavirus COVID-19 originated) or who had been in close contact with someone who recently traveled to and from China, according to the Centers for Disease Control and Prevention (CDC). But in this "unknown" case, the patient, who lives in California, said they haven't traveled to any locations where coronavirus has been detected or, as far as they know, been exposed to anyone with a known coronavirus infection, according to a press release from the CDC.

"This suggests that there is community spread of the virus," says infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. "Community spread" describes the spread of an illness wherein the source of the illness is unknown, explains Dr. Adalja. While health officials are still investigating the puzzling California case, it's possible that this person was unknowingly exposed to an infected traveler who'd recently returned to the U.S. from a location where the virus has been detected (at this time, coronavirus cases have been confirmed in at least 32 countries and territories), according to the CDC.

ICYDK, there are seven strains of coronavirus known to infect humans, according to the CDC. While most can cause minor ailments like the common cold, three types can cause serious illness: MERS-CoV (which causes Middle East respiratory syndrome, the illness that infected roughly 2,500 people and killed nearly 900 others in 2012), SARS-CoV (which causes severe acute respiratory syndrome, the illness that infected nearly 8,000 people and killed 800 others in 2003), and SARS-CoV-2 (aka this novel coronavirus that originated in Wuhan, China in December 2019 and causes coronavirus disease 2019, or COVID-19).

Currently, there are more than 81,000 confirmed cases of COVID-19 across the globe, including 53 in the U.S., according to the latest data from the World Health Organization (WHO).

This news naturally raises some major questions about coronavirus transmission, plus what you can do to stay safe. Here's what you need to know.

What has coronavirus transmission looked like so far?

COVID-19 is thought to have originally spread from animals to humans, says Dr. Adalja. It's unclear where, exactly, this coronavirus originated, but it's believed to have started in a large seafood market in Wuhan, China, he explains.

Now, coronavirus transmission is happening mainly from person to person through respiratory droplets (aka coughing and sneezing), according to the CDC. "An infected person coughs or sneezes, and the droplets go into the air and fall to the ground," says Rajeev Fernando, M.D., an infectious disease expert in Southampton, New York. The droplets can land in the mouths or noses of people who are near the infected person, and they can also be inhaled into the lungs, adds Dr. Adalja. The droplets are thought to have the ability to travel up to six feet before falling, according to the CDC-released info about coronavirus transmission. And while some reports indicate that people can spread the coronavirus before they show symptoms, an infected person is believed to be most contagious once symptoms are present. (

Can coronavirus transmission happen after touching a contaminated surface?

Inhaling or ingesting infected respiratory droplets seems to be the primary way that coronavirus transmission happens. But the virus can also spread by touching a surface that's been contaminated by the virus, says Pinki J. Bhatt, M.D., an infectious disease specialist at the Rutgers Robert Wood Johnson Medical School. Meaning, if a person with coronavirus touches say, a counter just before you do, and you put your unwashed hands in your mouth, nose, or eyes, there's a chance you could become infected with the virus. While experts still don't have definitive data about this novel coronavirus transmission, a recent review of 22 studies on human coronavirus strains (including SARS-CoV-2) suggests that these viruses may linger on surfaces like metal, glass, or plastic for up to nine days. If that freaks you out, know this: Touching contaminated surfaces is not thought to be the main form of coronavirus transmission, according to the CDC. Plus, the authors of the review said that the virus can be "efficiently inactivated" by things like disinfectant wipes.

"There is also some evidence that coronavirus is shed in the feces of infected people," says Richard Watkins, M.D., a clinical researcher and infectious disease physician in Akron, Ohio, and a professor of medicine at the Northeast Ohio Medical University. In mid-February, health officials in Hong Kong partially evacuated an apartment block over fears that coronavirus transmission was happening through the building's pipes. While early research suggests that coronavirus can be detectable in the fecal matter of infected people, health officials are still trying to figure out if this means COVID-19 can spread via sewage pipes, explains Dr. Watkins. (

How does coronavirus transmission compare to that of other infectious respiratory viruses?

At this time, the novel coronavirus transmission rate seems to be on par with that of influenza and the common cold, says Dr. Watkins. However, COVID-19 does seem to spread more quickly than SARS and MERS, notes Dr. Adalja. "That could partly be due to increased globalization, people traveling more, and better diagnostics," adds Dr. Bhatt.

That said, data on the novel coronavirus transmission rate is limited since the virus was only recently discovered. So, there's a lot that researchers still don't know about the virus. Ultimately, infectious disease experts recommend practicing proper hygiene to avoid contracting COVID-19 and other respiratory infections. (Here are some other tips on how to prepare for coronavirus and the threat of an outbreak.)

"The best way to prevent the illness and stay safe is to practice preventive actions," explains Dr. Bhatt. "This includes washing your hands often with soap and water." Dr. Fernando also recommends using hand sanitizer that contains at least 60 percent alcohol and regularly sanitizing commonly used surfaces in your home, like counters, bathroom fixtures, and doorknobs. (BTW, you don't need one of those N95 respirator masks.)

Limiting how much you touch your eyes, nose, and mouth is also a good idea, says Dr. Adalja. Additionally, he recommends avoiding close contact with anyone who seems to be ill.

As of now, COVID-19 is considered a low risk to the majority of Americans, according to the CDC. Even though that could change at any time, experts say there's no need to panic right now. Instead: "Wash your hands a lot and keep abreast of news in your local community about the virus," says Dr. Adalja.

The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it’s possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.