York schools will move to online instruction next week because a rise in COVID-19 cases has led to an untenable number of staff and student absences.

Superintendent Lou Goscinski informed the school community in an email Friday afternoon. He cited the growing positive test rate in York County, which is above 20 percent, and said the district has been struggling to staff buildings and classrooms since students returned from the holiday break.

York County is a particular hotspot for infections, Goscinsky wrote. As of Friday, York County had 549 COVID infections per 100,000 population, the highest infection rate in the state.

A total of 1,625 students attend York’s four schools, but it was not immediately clear how many people the district employs.

Co-curricular activities will be canceled as well. Students were already staying home Monday, a staff development day, although staff are expected to work. In-person instruction and co-curricular activities are expected to resume Jan. 18 after Martin Luther King Jr. Day.

Principals at each school are expected to communicate more details with families soon, Goscinski wrote.

“We look forward to getting back to in-person instruction and resuming co-curricular activities as quickly as possible,” he wrote. “Stay safe.”

Goscinski did not say how many teachers, non-teaching staff and students had called out sick or were absent this week. He did not immediately return a call seeking an interview.

York is the latest district to move to online instruction following a surge in cases statewide driven by the highly contagious omicron variant. Other states and school districts are already feeling the effects of a surge in cases among teachers, disrupting in-person learning.

Statewide, hospitalizations for COVID-19 were the highest of the pandemic Friday, and the state has seen more cases in recent days than at any time during the pandemic.

Shifting infection rates among Maine counties suggests the new variant has initially spread most quickly in coastal and more populous counties, driving up infection rates where they had been relatively low just three weeks ago. Experts predict cases will soon spike in every county, however, as omicron takes hold in rural areas, too.

Bonny Eagle, one of the largest school districts in the state with 3,430 students, moved to online learning Tuesday after too many bus drivers called out sick because of exposure to the virus, that district’s superintendent said.

While scientists believe omicron is less deadly in general and especially for vaccinated people, it is far more contagious than the original strain and the delta variant.

Portland Superintendent Xavier Botana announced changes to the district’s COVID-19 protocols during Tuesday night’s school board meeting.

Jeremy Ray, superintendent of schools in Biddeford, Saco and Dayton, said district schools are seeing more positive cases this week than ever, but he called switching to remote learning a “last resort” option.