BILLINGS, Mont. (AP) — Newly confirmed coronavirus cases in Montana spiked to another record on Thursday and health officials reported that the number of infections tied to schools had more than doubled in just a week.

The state health department reported 333 new confirmed cases of the respiratory virus, topping the previous single-day record set last Friday.

The number of schools with cases associated with them rose from 58 last week to 121 this week. All but four of the schools have reported new cases in the past two weeks.

Almost 500 infections in total have been tied to schools since classes widely resumed in late August. That includes about 200 cases at universities and about 200 in K-12 schools.

The remaining student and staff cases are still under investigation and the school setting was not identified in the data released by the Department of Public Health and Human Services.

There are about 147,000 K-12 students in Montana. The data does not include schools with 10 or fewer students.

Schools across the state have adopted a variety of approaches to handling the virus, from full-time in-person classes, to remote learning and a mix of the two.

In Bozeman, more than 100 parents and students protested outside a school auditorium Wednesday in support of a return to full-time in-person learning. The Bozeman school board voted earlier this week to continue with two days of in-person school and three of remote learning.

“Each family should be able to look at their risk level and make their own decision,” Molly Ogle whose children are in the sixth and 11th grades, told the Bozeman Daily Chronicle.

The overall spike in cases in recent weeks was driven by schools reopening, Labor Day weekend gatherings and the virus’ continued spread through facilities such as nursing homes and jails, state epidemiologist Stacey Anderson recently said.

Jails and other correctional facilities have seen more than 300 cases among inmates and staff since the pandemic began, while nursing homes and other facilities for the elderly have seen more than 450 cases.

People between 20 and 29 years old now represent the age group with the most cases, a shift from the early months of the pandemic when most cases were being found among older adults, according to an analysis released this week by the state.

COVID-19 has killed 165 people and infected more than 11,000 in the state since Montana confirmed its first case on March 11.

Native Americans continue to be hit disproportionately hard. They account for about 7% of Montana’s population but 24% of confirmed COVID-19 cases and 37% of deaths where the race of the victim was known.

The number of infections is thought to be far higher in the state because many people have not been tested, and studies suggest people can be infected with the virus without feeling sick.

For most people, the coronavirus causes mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.

In other coronavirus-related news:

— Applications for temporary unemployment assistance in Montana declined during the week ending Sept. 12, the U.S. Employment and Training Administration reported Thursday. The number of applications submitted fell to 2,848, a decrease of 2.2% from the prior week but still up more than 300% compared to the same week last year.

Since March 14, the state has processed about 148,000 claims for unemployment, representing almost a third of the Montana workforce eligible for unemployment insurance. As of Sept. 5, more than 22,000 people, or 4.8% of all eligible employees in the state, were receiving unemployment benefits in Montana.