In Colorado, Denver Mayor Michael Hancock said Covid-19 cases were rising at a "concerning rate," and warned new restrictions could be needed, with the city's seven-day average daily case rates as "high right now as they were at the height of the pandemic back in May."
Officials across the country are warning of similar patterns.
White House coronavirus task force coordinator Dr. Deborah Birx last week cautioned that the Northeast was seeing "early suggestions" of alarming trends.
Kentucky's governor said recently the state is seeing a third major escalation in infections.
And in Wisconsin, a field hospital is opening this week in response to a surge in Covid-19 patients -- days after the state reported record-high numbers of Covid-19 cases, hospitalizations and daily deaths.
The US is now averaging more than 49,000 new infections daily -- up 14% from the previous week, according to data from Johns Hopkins University. Last week, the nation recorded more than 50,000 new cases for at least four days in a row. The last time that happened was in early August.
I think we're facing a whole lot of trouble," Dr. Anthony Fauci told CNBC on Monday. "We've got to turn this around."
That doesn't have to mean another lockdown, the infectious disease expert has previously said, but means more people heeding to safety guidelines like wearing masks and social distancing.
Otherwise, the US could be in for a devastating winter. Researchers from the University of Washington's Institute for Health Metrics and Evaluation project that more than 135,000 Americans could die within the next three months.
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