Officials in Philadelphia are recommending residents start wearing masks indoors again due to a spike in COVID-19 cases.
Data shows the city is currently averaging 94 new cases of COVID-19 per day.
This marks a 50% increase in infections over the last 10 days.
Additionally, over the last two weeks, 3.3% of COVID-19 tests in Philadelphia have come back positive compared to 1.4% just one month earlier.
"It's not huge numbers we're seeing, but it's enough to take notice," Dr. Darren Mareiniss, an emergency medicine and infectious disease expert at Einstein Medical Center Philadelphia, told ABC News.
Earlier this year, Philadelphia set three COVID-19 benchmarks, and two would have to be met to trigger the return of indoor mask mandates.
These benchmarks include average new daily cases above 100 but below 225; hospitalizations above 50 but below 100; and cases increasing by more than 50% in the previous 10 days.
So far, just one benchmark has been met: the increase of cases by more than 50%.
However, the city is closing in on meeting the hospitalization benchmark. As of Monday, 48 patients are hospitalized in Philadelphia with COVID-19.
This has led officials to recommend residents wear masks indoors ahead of a potential mandate going into effect.
"As we see more cases of COVID-19 in the city, everyone's risk goes up," Dr. Cheryl Bettigole, commissioner for the city's Department of Public Health, said in a statement. "That means that now is the time to start taking precautions. It's not required yet, but Philadelphians should strongly consider wearing a mask while in public indoor spaces."
The department did not return ABC News' request for comment.
Mareiniss believes the increase is partly due to the spread of BA.2, a subvariant of the original omicron variant.
BA.2 makes up more than 84% of COVID-19 samples in the Northeast that have undergone genome sequencing, according to the Centers for Disease Control and Prevention.
This has closely mirrored what's occurred in several countries in Europe, including the United Kingdom, which hit a record-high 1 in 13 people being infected with the virus last week, according to the government's Office for National Statistics.
Mareiniss added that the rise in cases in Philadelphia is also because several mitigation measures have been relaxed since the end of the omicron wave.
"We've relaxed a lot of restrictions, people are not masking indoors; it's much easier to transmit the virus when people are indoors unmasked," he said. "So, we're going to see an uptick. The question is how much of an uptick."
He stressed the importance of people getting vaccinated if they haven't already and said to follow the health department's recommendations of wearing masks in indoor settings.
"Right now, I would recommend indoor masking for everyone given the rise of cases," Mareiniss said. "Your behavior should be dictated by the level of disease in the community ... and, as levels rise, you should consider masking. I would try to mask indoors and avoid indoor dining."