school bus
In this photo, children walk past a School Bus in Monterey Park, California, April 28, 2017. Getty Images

An elementary school in New Hampshire canceled classes on Friday after one-third of its students said they were too ill to attend, according to local station WMUR9.

Dozens of students, as well as 15 teachers, called in sick on Thursday at the Whitefield Elementary School. School officials say it's the biggest number of absences it has seen in decades.

Some of those who called out had confirmed it was because of the flu. Most students and teachers said they were experiencing viruses with flu-like symptoms. U.S. health officials have said this week that the flu season has heightened since it began last October.

School officials decided to close down the school on Friday. Instead of pupils in class, custodians were left cleaning and sanitizing the school, disinfecting surfaces and common areas.

"Our custodial staff have gone through and done the routine cleaning of all the handles, doorknobs and table surfaces, chairs and the like, but we have also added in a fogger," the school’s principal, Michael Cronin, told WMUR9. "It is supposed to handle all of the germs. It is synonymous to spraying a big can of Lysol."

School officials hope the cleaning and disinfecting will help, since students and teachers will have to catch up on missed work. While Cronin hopes students and staff will return after the weekend, he urged those who do not fully recuperate to stay at home until they’re better.

flu
Here, syringes filled with influenza vaccination are seen at a Walgreens Pharmacy in Concord, California, Jan. 14, 2014. Justin Sullivan/Getty Images

The school’s closure comes as the country deals with a harsh flu season. This week, the Centers for Disease Control and Prevention announced 16 more children have died from flu-related symptoms, bringing this season’s pediatric death toll to 53.

The CDC said the flu has spread to 48 states and Puerto Rico. Hospitalizations related to the flu have also increased. Acting CDC Director, Dr. Anne Schuchat, said on Friday that “hospitalizations are now the highest we’ve seen. Even higher than the 2014-’15, our previous high season.”

“Unfortunately, our latest tracking data indicate that the flu activity is still high and widespread across most of the nation and increasing overall,” said Schuchat. “Influenza A H3N2 viruses continue to dominate this season. However, we are seeing other flu viruses including H1N1, and influenza B causing illness as well, and in some cases, disproportionately affecting certain age groups.”

The CDC points out that young children, the elderly, pregnant women and those with heart or lung disease have a harder time with the flu. Health officials say people who are sick should stay at home to avoid spreading respiratory viruses to others. The CDC also recommends people to wash their hands often and to cover their mouth when they sneeze or cough.