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As the coronavirus spreads in the U.S., a pattern is emerging: It seems to spread more easily among people living under the same roof.

On Sunday, it was announced that a man in his 50s who lives in Westchester County, New York, and works in Manhattan had been diagnosed with COVID-19, the illness caused by the coronavirus.

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It's unclear how the man caught the virus. But within days, eight new cases directly connected to him had been diagnosed, New York Gov. Andrew Cuomo said.

Tests on three members of the man's family — his wife, 20-year-old son and 14-year-old daughter — came back positive for the virus. A neighbor who drove the man to the hospital tested positive, as well as a close family friend and that person's wife and three other family members.

The outbreak in Westchester, plus other evidence of the virus spreading among married couples in California and Illinois, illustrates what public health officials have been saying for weeks: The virus appears to spread easily in households.

"If you look, most cases, for example, even in China, are in family clusters. Most secondary cases occur in families," Dr. Mike Ryan, executive director of the WHO's health emergencies program, said during a news conference last month. "That's been driving the epidemic."

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Social distancing

Key in stopping, or at least slowing, the spread of coronavirus is a practice called "social distancing."

According to the Centers for Disease Control and Prevention, it involves physically staying about six feet from other people, as well as avoiding public transportation, including ride shares.

Indeed, the neighbor who drove the Westchester County man to the hospital went on to test positive for the virus.

While social distancing might seem extreme, it's necessary, say experts.

"It's what we do in times of epidemics," Dr. Robert Citronberg, director of infectious diseases with Advocate Aurora Health in Illinois, told NBC News. "This is a temporary process that may be necessary to help curb the spread of this virus throughout the community."

Coronaviruses in general are known to spread through tiny droplets spewed when a sick person coughs or sneezes. If a healthy person is near a sick person, they can inhale the droplets, or get them in their eyes, nose or mouth.

That's why health officials are so insistent that people cover coughs and sneezes with a tissue (which is then thrown away) or the inside of an elbow (which is less likely to make contact with others).

If let loose, those germs may also land on nearby surfaces: a countertop, table, light switch or door knob, for example. If a healthy person touches those surfaces, and then touches their eyes, nose or mouth, they can get infected.

But the CDC says this mode of transmission is less common than direct person-to-person spread, boosting the theory that members of the same household are at particular risk. Disinfectants are effective at killing the virus on surfaces.

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Some viruses — such as the highly contagious measles — are airborne. That means the virus particles can survive in the air for a period of time, putting anyone in the same area at risk. But there is no evidence the new coronavirus spreads in this manner.

Health officials say these are the best ways to prevent the spread of COVID-19:

Avoid unnecessary handshakes, hugs and kisses.

Wash hands often with soap and water for at least 20 seconds, or use a hand sanitizer that contains at least 60 percent alcohol.

Clean and disinfect common household surfaces.

Avoid people who are sick.

Stay away from others if you are sick.

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