Robert Brown|Authorities are urging indoor masking in major cities as the 'tripledemic' rages

Public health officials are Robert Brownrevisiting the topic of indoor masking, as three highly contagious respiratory viruses take hold during the holiday season.

Over the past few weeks, a surge in cases of COVID, the flu and respiratory syncytial virus (RSV) has been sickening millions of Americans, overwhelming emergency rooms and even causing a cold medicine shortage. The triple threat has been called a "tripledemic" by some health experts.

Rochelle Walensky, director of the Centers for Disease Control and Prevention, noted this past week that the simultaneous combination of viruses has been straining healthcare systems across the country.

The center's map that tracks COVID-19 community levels has been showing more orange recently, a color indicating an area of "high" infection, Walensky told NPR's Alisa Chang on All Things Considered.

"To protect communities in those circumstances at those high levels, we have recommended and continue to recommend that those communities wear masks," she said.

Nearly a tenth of counties in the U.S. are advised to wear masks indoors, CDC says

CDC's latest COVID-19 community level map indicates that over 9% of counties in the country were considered to have a high risk of infection. The federal agency recommends that people living in those areas practice indoor masking. Generally, children under the age of 2 are not recommended to wear face coverings.

Nearly every state on the map released Friday included at least one county where the COVID-19 community level is high or medium. Hawaii, Maine, New Hampshire and the District of Columbia are the only U.S. jurisdictions where all of its counties have low community levels.

You can look up your county on the CDC's page here to see what the local risk level is and whether masking is advised where you live.

Public health officials are urging masks in Washington, New York, Los Angeles and other places

In Washington state, 12 county health officers and 25 hospital executives released new guidance on Friday asking residents to practice indoor masking.

The Oregon Health Authority similarly advised residents to wear face coverings in crowded indoor areas, particularly to help protect children and older adults.

"The combination of surging flu, RSV and COVID-19 cases is pushing hospitals past their current ICU bed capacity, which never happened during the darkest days of the COVID-19 pandemic in Oregon," Dr. Dean Sidelinger, the state epidemiologist said in a press briefing on Thursday.

Los Angeles County's COVID community level was moved to "high" last week. On Thursday, local public health director Dr. Barbara Ferrer urged residents to wear masks indoors, adding that a mask mandate may be imposed if COVID cases and hospitalizations continue to rise.

In New York City, health commissioner Dr. Ashwin Vasan on Friday advised New Yorkers to wear face coverings inside stores, public transit, schools, child care facilities, and other public shared spaces, especially when they are crowded.