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Those are two pieces of advice that could be crucial in reducing the spread of the coronavirus.

Public health officials say the spread has been mainly driven through people spending time indoors with others who have the disease.

"Looks like the main driver is not widespread community infection — looks like it's household-level infection," Dr. Bruce Aylward, a senior adviser to the World Health Organization, 

Indeed, data from China's cases show that most of the spread is happening among family members who live together.

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Perhaps the reason that the virus spreads among family members is the way people become infected. "The main mode of transmission is respiratory droplets" that can be produced by 

, associate professor of microbiology and immunology at the University of Michigan. "These droplets then can find their way into the mouths, noses of other people nearby."

(Sneezing, another way droplets are spread, is 

 of COVID-19, indicating that it's not usually an upper respiratory infection, Aylward said.)

But spread isn't exclusively a family matter. The close contact that leads to infection can apply to a range of behaviors, says 

, a virologist who studies flu transmission at the University of Pittsburgh. "You can do it through shaking hands or kissing somebody who is sick, or you can do it through indirect contact transmission, which is through a contaminated surface, something like a doorknob or a handrail ... [or] you pick up somebody else's phone."

(To learn how Lakdawala suggests cutting down on the risk of transmission at home, 

Researchers aren't sure how long droplets of the new coronavirus remain infectious on phones, but similar coronaviruses can survive on surfaces from a few hours up to a few days, depending on the environment, 

Spread takes place more readily if you're within coughing range of someone sick, "like if you're standing next to your kid and they cough in your face," says Lakdawala. You could breathe in the droplets. Or they may land on a surface that somebody then touches.

While there's no way for health authorities to regulate family interactions, steps can be taken to reduce the likelihood of close contact in crowds.

 — as when China extended the national Lunar New Year holiday to keep people from traveling or working, closed offices and canceled public transportation — have helped slow the transmission of the disease there. Such steps could be effective in other countries, including the U.S., where the virus is spreading in some communities.

, such as the 1957 flu pandemic and the 2003 SARS epidemic, found that public health policies that kept people from gathering in public spaces — such as closing schools and canceling big events — helped slow the spread of disease.

In the current outbreak, the evidence for the way the coronavirus has spread comes from analyzing case clusters in China. Findings were published on Feb. 28 in a 

In mid-February, a team of international experts visited areas in China hard hit by the coronavirus. The mission was co-led by Aylward and Wannian Liang, head of the expert panel for China's National Health Commission.

The team toured hospitals, health clinics and community centers to determine how the coronavirus is spreading in China.

Aylward says the pattern of family spread could be a big reason for China's apparent success in slowing the spread of the virus. Once one member of a family is infected, it's usually easy to find other family members who may have had close contact and then put them in quarantine for 14 days.

Data from China's government show that the country's coronavirus infection rates peaked in late January and have declined ever since.

Outside China, much of the spread has come from mass gatherings. On the Diamond Princess cruise ship, more than 700 passengers and crew members caught the coronavirus. More than 2,000 infections have been linked to a 

"It's very much driven by the context of a gathering" and how people disperse after it's over, spreading it to other individuals or groups, said 

, executive director of the WHO Health Emergencies Programme, at a press conference on Feb. 24.

There is some encouraging news about the coronavirus' spread. So far, it seems to spread less easily than flu or measles.

"With influenza, people who are infected but not yet sick are major drivers of transmission, which does not appear to be the case for COVID-19," 

said WHO Director-General Tedros Adhanom Ghebreyesus

 at a news conference on March 3. And the measles virus is so contagious that droplets can survive in the air for two hours.

And you should definitely think twice before kissing. French Health Minister Olivier Véran has advised people to cut back 

. Even a kiss on the cheek from a coronavirus case could leave droplets that you would breathe in.

Tips on preventing coronavirus spread at home

Lakdawala, the University of Pittsburgh virologist, studies how viruses spread — and what can limit them.

She has some simple tips for stopping the spread of the coronavirus or any other virus at home if someone is sick:

Health

COVID-19

Pien Huang

Author

After looking at the patterns of spread in China, researchers have come up with advice for effective strategies to reduce the risk of infection.

How coronavirus spreads: A cough in your face ... or a kiss on your cheek

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