Concerns about unexplained illnesses in a special-needs school building have led the Osseo Area Schools to spend more than $73,000 to test for mold and study the air quality, heating and air conditioning, among other things.

Since September, staff members and students have reported symptoms such as burning in the throat and eyes, fast heartbeat, dizziness and numbness in the face.

The Minnesota Department of Health got a number of complaints from parents and staff who demanded an investigation.

Dan Tranter, indoor air supervisor for MDH, said the concerns did not trigger an investigation, but health officials gave the district ideas on checking for potential problems, such as carbon dioxide, mold and ventilation.

“Usually we get one or two calls per month,” Tranter said, referring to indoor air quality concerns. The number of calls in this case “is a little unusual,” he said.

In an e-mail to the Star Tribune, Osseo Area Schools Superintendent Kate Maguire said the school has exhausted all possible tests. Her note did not say what issues, if any, were found.

“Our comprehensive approach included extensive testing, identification and execution of necessary repairs and or maintenance, and an independent review of our work to address any potential concerns. I am confident that we have taken every appropriate action to get to the bottom of reported concerns,” she said in a statement last week.

The 64-year-old Osseo Education Center, 324 6th Av. NE., serves about 100 students in two special-needs programs. ACHIEVE serves students in grades 7-12 who have significant disabilities, while the Osseo Secondary Training Center serves students ages 18-21 who need extra support to live independently.

In mid-December, the school sent a letter to parents and teachers informing them that the numerous tests failed to find any building-related link that could explain their symptoms. To address the complaints, the school cleaned a cafeteria and closed a room that needed ventilation improvement. The room was being used as an office by a staff member but was initially designed as a closet, according to district spokeswoman Barbara Olson.

Parents said they were kept in the dark about the severity of the situation until someone close to the case alerted them.

Heidi Hughes of Maple Grove moved her seventh-grade son from the school to one in New Hope. Hughes said her son complained of a constant stomachache, dizziness and headaches that made him nauseous. She said that his symptoms disappeared after only a week in the new school.

“He was always sick, and his teacher was constantly in and out,” Hughes said. “The school couldn’t tell me if it was a safe environment for him. This is a school for special needs kids. They’re medically fragile kids.”

Olson said a complaint has been filed against the district. She declined to provide further information.