In the U.S., 59.72% of counties are reporting high community transmission. Five weeks ago, only 8% of counties were reporting high transmission, according to federal data.

Louisiana now has the highest case rate in the country with more than 600 new cases per 100,000 residents, according to federal data.

Louisiana Gov. John Bel Edwards on Monday reinstated a statewide indoor mask mandate for everyone ages 5 and above.

Louisiana is followed by Florida, Arkansas and Mississippi with 500, 400 and 300 new cases per 100,000 residents respectively.

-ABC News’ Arielle Mitropoulos

Sen. Lindsey Graham, who is vaccinated, said he’s tested positive for COVID-19.

"I started having flu-like symptoms Saturday night and went to the doctor this morning," the Republican senator tweeted Monday. "I feel like I have a sinus infection and at present time I have mild symptoms."

Graham continued, "I am very glad I was vaccinated because without vaccination I am certain I would not feel as well as I do now. My symptoms would be far worse."

In Louisiana, which has the nation's highest case rate per 100,000 residents, COVID-19 hospitalizations are reaching peak levels, with more than 1,700 patients now receiving care.

"We're seeing people that are way too young to be so sick," David Wrightson, a respiratory therapist and ECMO (extracorporeal membrane oxygenation) specialist for the Willis-Knighton Health System in Shreveport, Louisiana, told ABC News. "We see families destroyed. We see children without one or more parent because of this virus. We see a new mom who will never go home to see her newborn, will never see her child grow up."

He went on, "When you see someone that's 30 years old with no medical problems at all, nobody knew anything was wrong, and we have this person literally on death's doorstep, doing everything in our power to turn them around and return them to their family. The vaccine is something worth getting."

More people need to see and understand the reality of this disease, he said.

"I wish I could show them a few steps in our day to see what we see and to see what we have to do, and to go home at night and, and have nightmares about those things, and sometimes cry yourself to sleep," he said.

-ABC News’ Erica Baumgart and Arielle Mitropoulos

Denver is mandating vaccinations for city employees and those in high-risk jobs like first responders, correctional workers and school personnel. The mandate also applies to staff at long-term care facilities, shelters and hospitals.

Mississippi is facing "a phenomenal increase in daily reported cases of COVID, and this is entirely attributable to the delta variant, which is sweeping over Mississippi like a tsunami," state health officer Dr. Thomas Dobbs said Thursday.

Dobbs said 97% of new cases are among the unvaccinated, and that 89% of hospitalizations and 85% of deaths are unvaccinated.

Dobbs pleaded with the public to get vaccinated, stressing that the unvaccinated population is driving the current surge, but that vulnerable, vaccinated people are suffering the fallout.

"There is going to be some collateral damage, unfortunately, even folks who've done everything they can to protect themselves," Dobbs said.

"The minority of folks who are vaccinated and hospitalized are overrepresented by the older and those with weaker immune system, so we're seeing a pretty dramatic spillover effect from the transmission in the community to more vulnerable parts of our population," he said.

-ABC News' Soorin Kim