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R-0 may be the most important scientific term you’ve never heard of when it comes to stopping the coronavirus pandemic.

USA TODAY

Officials have been able to control COVID-19 transmission rates by implementing policies that encourage residents to eat and drink, exercise and spend time with friends and loved ones at a safe distance outside. 

But health experts are concerned cases could spike again as cooler temperatures in the fall and winter force people back indoors. 

The nation’s leading infectious disease expert Dr. Anthony Fauci also is concerned upcoming holiday celebrations could increase transmission rates and advised Americans to skip any big Thanksgiving plans. 

Speaking to “CBS Evening News” Wednesday, Fauci cautioned against “gathering together in an indoor setting” with large groups of out-of-town guests. “It is unfortunate because that’s such a sacred part of American tradition – the family gathering around Thanksgiving,” he said. “But that is a risk.” 

Some experts suspect indoor transmission is what facilitated the summer surge of COVID-19 cases in southern states as residents retreated to public places with air conditioning to escape the heat. The three most populous states – California, Texas and Florida – each tallied more than 500,000 infections at the height of the surge in August, according to Johns Hopkins data.

“Indoors in public spaces is one of the places where the largest amounts of risk and transmission are likely to be happening,” said William Hanage, associate professor of epidemiology and a faculty member in the Center for Communicable Disease Dynamic at Harvard T.H. Chan School of Public Health.

What makes congregating indoors so dangerous and how can you stay safe?

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New York City reached a recovery milestone on Wednesday as indoor restaurant dining was permitted for the first time since March. (April 30)

AP Domestic

‘A minority of infections leads to the majority of transmission’

Dr. Lewis Nelson, professor and chair of emergency medicine at Rutgers New Jersey Medical School, said one of the main reasons there’s a higher risk of transmission indoors than outdoors is lack of ventilation.

Natural air currents outside disperse virus particles more quickly and effectively than inside. There’s minimal to no air circulation indoors, allowing virus particles to linger in the air or fall on high-touch surfaces.

“If I were to smoke a cigarette (inside), you would see the smoke particles linger,” he said. “Whereas outdoors the smoke kind of leaves.”

Additionally, indoor public places have more surfaces. As respiratory droplets or aerosol particles fall, they land on table tops, chairs, door handles and other objects people frequently touch.

“Outdoors have less surfaces,” Nelson said. “Nobody is touching the ground and then touching their eyes, nose or mouth.”

People also tend to be closer indoors because they’re confined by walls. Hanage said bars are a major source of transmission in communities because people tend to gather there for long periods of time as judgement