Weekly cases among the age group jumped 55 percent across the country during that time and made up a bigger share of overall cases, according to the CDC’s Morbidity and Mortality Weekly Report. The agency said the increase in cases couldn’t fully be explained by ramped-up testing as colleges reopened for the fall.

The Northeast saw the biggest spike in virus cases among 18- to 22-year-olds, with a 144 percent increase. Cases in the Midwest among that age group also rose dramatically, with a 123 percent increase.

Also on Tuesday, a public university in North Carolina mourned the death of a student from complications that followed a covid-19 diagnosis.