According to researchers at PolicyLab at the Children's Hospital of Philadelphia, Chicago has a high transmission rate and inadequate social distancing measures. Boston's transmission rate is growing and many are traveling for leisure, according to cell phone data, according to PolicyLab. And Baltimore is at risk because of its high density and poverty rate, and large number of multi-generational households.
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"We're just seeing significant transmission in all three of those cities happening late in the summer, acknowledging they have only weeks left before nights get colder and transmission dynamics may actually worsen," said Dr. David Rubin, director of PolicyLab at the Children's Hospital of Philadelphia. "I worry about a perfect storm."
Traveling ICU nurse Trinity Goodman knows the challenges of hot spots all too well. She was working in New York when the pandemic first hit.
"I almost felt this almost like a deeper like calling to go," Goodman said.
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And more recently, she's been working along the Texas border, where she says all her patients were under 40 and not one of them lived.
"We just had literally no resources," she said. "That's like we had no right literally had no resources."
In the past 24 hours, the United States reported the nation's highest number of deaths in a single day. Robert Redfield, director of the Centers for Disease Control and Prevention, issued a stark warning, saying everyone in America needs to wear a mask, or this coming fall could be the worst "we've ever had."
ABC News contributed to this report.