Minnesota schools are reporting a surge in flu outbreaks as an unusual mix of early flu strains continues to spread statewide and take a toll on children.

The state recorded 60 outbreaks of flu-like illness last week — a nearly fivefold increase from the prior week, according to an influenza tracking update released Thursday by the Minnesota Department of Health.

“We use a threshold of 5% absenteeism, and we’re seeing much higher levels than that,” said Kris Ehresmann, director of the state Health Department’s infectious disease division.

Some schools are missing as many as one-fifth of their students.

The Health Department also declared influenza to be “widespread” in Minnesota, which means that cases have now been detected in every reporting region in the state.

That designation prompted several hospitals to impose routine flu-season visitor restrictions. Anyone experiencing flu-like symptoms and children under age 5 were asked to refrain from visiting patients at Allina Health hospitals, which include Abbott Northwestern in Minneapolis and United in St. Paul, and at the M Health Fairview system, which includes the University of Minnesota Medical Center and Masonic Children’s Hospital in southeast Minneapolis.

Health officials said the upcoming holiday break is arriving at a good time in some respects because it could disrupt the spread of school outbreaks. But, they said, it also means that sick children might spread germs as they visit friends and relatives.

The number of school outbreaks — which are reported when flu-like illness causes more than 5% of students to be absent, or three or more students to be missing from the same elementary school classroom — contrasts sharply with the absence of any outbreaks last week in long-term care facilities such as nursing homes.

Children also represented a higher than usual share of the 262 flu-related hospitalizations reported so far this season. Six flu-related deaths have been reported as well, though none involved children.

Testing data continued to show the unusual early-season emergence of a B strain of influenza. Normally, A strains emerge first in the winter and then B strains come later. B strains have historically spread more quickly among children.

While flu seasons with lots of B influenza infections tend to be milder, health officials said any flu infections should be taken seriously. Vaccine remains widely available and includes protection against both A and B strains.