A high school in Virginia had to cancel its weekend activities after nearly half its students came down with flu-like symptoms.

“There are approximately 1,000 students absent with flu-like/gastrointestinal symptoms at Stafford High School,” Sandra K. Osborn, chief communications officer with Stafford County Public Schools, said in a statement. “Our Health Services team is working with the local health department to identify the root cause of the illness.”

Stafford High School, located in Fredericksburg, has approximately 2,100 students. In a letter to parents, Principal Allen Hicks said school officials “remain very concerned” and canceled athletics and extracurricular activities through Sunday.

“We remain very concerned and will continue to monitor the situation alerting you to any changes we may need to make to our operations,” the letter to parents said. “Our custodial staff will conduct an extensive and thorough wipe down of the entire school this evening. High-touch point area cleaning, along with electrostatic cleaning, will continue throughout the day and evening tomorrow.”

Several teachers have also missed classes after coming down with flu-like symptoms. While health officials with the Rappahannock Area Health District continue to investigate the sudden outbreak, Stafford High School will remain open.