Flu-like illnesses caused 167 outbreaks in Minnesota schools last week, making this season the worst for schoolchildren in five years.
With most classes dismissed this week for the holiday break, the next front for the flu's spread is likely to be at home or at community events, but the dominant flu strain this season is one that tends to affect children the most.
The number of school outbreaks jumped from 60 in the previous week, according to the weekly flu update provided by the Minnesota Health Department on Thursday.
By comparison, there was just one outbreak in long-term care facilities last week, making it one of only eight reported so far this season.
Minnesota has not seen so many school outbreaks since the 2014-2015 season, when nearly 300 schools reported that at least 5% of their students or three or more students in one elementary class had called in sick around this time of the year.
That means there are a lot of sick children, but because the definition of a flu-like illness is broad and many cases are not confirmed by a laboratory, some of those affected could be showing symptoms of cold viruses, which are also common this time of year.
Flu symptoms typically develop abruptly, according to the Centers for Disease Control and Prevention, and often include a fever and body aches, which are less prevalent with the common cold.
Those and other symptoms, such as head congestion, coughing, sore throat and sneezing, are sending many people to the doctor, with 6.5% of clinic visits caused by flu-like illnesses, up from 3.4% in the previous week.