Pedestrians wear masks as they cross Brand Boulevard, Thursday, July 23, 2020, in Glendale, Calif. Three out of four Americans,…
Pedestrians wear masks as they cross Brand Boulevard, Thursday, July 23, 2020, in Glendale, Calif.

With the coronavirus spreading widely across the United States, the White House's pandemic task force coordinator is advising those living with vulnerable people to wear a mask at home, as well as in public places.  

"If you're in multigenerational households and there's an outbreak in your rural area or in your city, you need to really consider wearing a mask at home," Deborah Birx said Sunday on CNN's “State of the Union.” 

The United States is recording more than 60,000 new cases and more than 1,000 deaths per day on average, according to the COVID Tracking Project.

Birx said the pandemic was entering a “new phase” in the United States.  

While outbreaks were focused in large cities in the early months, “this epidemic right now is different and it's more widespread and it's both rural and urban," she said. 

President Donald Trump called Birx’s comments “pathetic.” He tweeted she “took the bait” after criticism from House Speaker Nancy Pelosi, who said Birx had previously presented too optimistic an outlook.

 The coronavirus can spread from infected people before they show symptoms, or from people who never show symptoms. One study estimates that more than half of all cases derive from presymptomatic or asymptomatic people.

The safest best, Birx said, is "assuming that you're positive if you have individuals in your households with comorbidities" such as diabetes or heart or lung disease. 

Shortcomings in coronavirus testing are exacerbating the problem.  

While the United States is now performing more than 800,000 tests per day on average, nearly half of test-takers are waiting more than three days for results. Some places report waits of a week or more. 

"What is occurring in many parts of the country is a situation in which people don’t know they’re infected, and the turnaround time for outpatient testing is too long to be useful," said Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security.  

"If someone is an essential worker or engaging in activities that are likely to bring them in contact with the virus, it may make sense to assume one is infected and take actions to protect vulnerable individuals with whom you live," he added. 

Public health officials say that while masks provide some protection for the people who wear them, their greatest benefit is preventing wearers from spreading the disease, especially when they could be carrying the virus and not know it.  

Experts are increasingly convinced that the virus can hang around in the air in droplets expelled by an infected person for longer than previously suspected, especially indoors.  

Epidemiologists have assumed that large droplets an infected person releases while coughing or sneezing, or even shouting or singing, fall to the ground within two meters, hence the social distancing recommendation.  

"Then we find out from the aerosol particle scholars that say, 'You know, there are larger particles than that that stay floating around a lot longer, so you shouldn't assume they all go to the ground,'" said National Institute of Allergy and Infectious Diseases Director Anthony Fauci in an interview Monday with the Journal of the American Medical Association.

Scientists are still debating how big a role airborne transmission plays in spreading COVID-19. But, Fauci added, "The one thing that it does tell you that's important is that you really better wear a mask." 

While breezes quickly blow away floating virus particles outdoors, "We need to pay a little bit more attention now to the recirculation of air indoors," Fauci added, "which tells you that mask-wearing indoors … is something that is as important as wearing masks when you're outside dealing with individuals where you don't know where they came from."  

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