The coronavirus could pass between people who are up to 6 feet apart, the CDC warns

Six feet. That's how far the Centers for Disease Control and Prevention (CDC) suggests you stay from anyone who might be sick.

The agency is recommending that people avoid "close contact" with anyone showing flu-like symptoms. Specifically, the CDC defines close contact as "being within approximately 6 feet (2 meters) of a COVID-19 case for a prolonged period of time."

That's because the viral particles travel between people in tiny droplets or saliva and mucus, which typically spread 3 to 5 feet. If a sick person sneezes, coughs, or eats within that distance of someone healthy, the particles could land on them; if the particles enter the person's eyes, nose, or mouth, the person can become infected.

In the past, infection-control professionals have defined "close contact" as 3 feet that was the CDC's recommended distance for people during the SARS outbreak. But the agency has doubled that for the coronavirus, since it is possible for droplets to travel up to 6 feet.

How the coronavirus spreads

Scientists think the new coronavirus is carried in liquid droplets more than 5 micrometers in diameter. The common cold, which is also a coronavirus, travels in these big, wet droplets, too.

Scientists aren't sure whether the coronavirus also travels in smaller, drier droplets known as aerosols (which are less than 5 micrometers in diameter). Aerosols remain airborne for longer because of their size and are usually inhaled. Tuberculosis and measles are mainly transmitted through aerosols. Even if the coronavirus does travel in aerosols, though, it's not the main mechanism of transmission.

Disinfection equipment is carried by a worker as precautionary measures against the spreading of novel coronavirus, at Budapest Liszt Ferenc International Airport in Budapest, Hungary, 2 Zoltan Balogh/MTI via AP

Scientists aren't yet sure how long droplets containing the virus can live on surfaces. According to the World Health Organization , "studies suggest that coronaviruses (including preliminary information on the COVID-19 virus) may persist on surfaces for a few hours or up to several days."

The wide range there depends on factors like the type of surface and temperature or humidity of the surrounding environment. (The length of time a virus survives on a surface also depends on what kind of droplet it's traveling in saliva, phlegm, or aerosol.)

Robert Redfield, director of the CDC, told lawmakers on Thursday that "on copper and steel it's pretty typical, it's pretty much about two hours," according to Reuters .

"But I will say on other surfaces cardboard or plastic it's longer, and so we are looking at this," Redfield added.

A review of 22 studies of other coronaviruses found that at room temperature, human coronaviruses could remain infectious on inanimate surfaces for up to nine days. But the paper also said the viruses could be rendered inactive by common disinfectants and temperatures higher than 86 degrees Fahrenheit.

The best ways to avoid getting sick

The best ways to avoid getting the coronavirus (or any virus), according to the CDC, are to wash your hands frequently and avoid touching your face .The agency also recommends disinfecting commonly touched surfaces doorknobs, light switches, phones, and keyboards using household cleaning spray or wipes.

The CDC suggests that anyone who might come into close contact with people who have COVID-19 take additional precautions , such as wearing a mask. While masks are not recommended for the general US public, people caring for confirmed coronavirus patients in medical settings or at home should wear them.

In addition, the CDC recommends that people exhibiting flu-like symptoms stay home. If a person with flu-like symptoms does need to go out, they should also wear a mask, the CDC says.

coronavirus BSIP/UIG via Getty Images

The coronavirus has infected more than 89,000 people and killed more than 3,000 in total. Cases have been reported in at least 69 countries beyond China.

The US has reported nearly 100 coronavirus cases and six deaths.