Parents in multiple California counties have been notified that a teacher may have contaminated flutes sent to elementary students with bodily fluid — specifically, semen.

NBC News reports that federal authorities are investigating reports that flutes sent to elementary school children as part of a nonprofit outreach program called “Flutes of the World” may have been contaminated by a performer and teacher who was involved in the distribution.

“You have to read in between the lines — and most likely it’s not sweat,” a parent of a student at Courreges Elementary School in Fountain Valley told the news outlet.

“It makes me sick to my stomach,” said another parent.

According to the Sacramento Bee, Saugus school district Superintendent Joan Lucid said in an email to parents Saturday alerting them to the vile contamination.

“The performer distributes a flute-like musical instrument made of PVC pipe or bamboo to students during a music lesson, and the allegation is that he contaminated some of these instruments with semen,” Lucid said in the email.

The alleged contamination first came to light in a report from the Fountain Valley schools superintendent. The flutes were reportedly distributed throughout Southern California. According to NBC News, the contaminated flute shipment may have affected up to 13 school districts.

“We are still working to determine which specific schools,” Capistrano school district spokesperson Ryan Burris reportedly said in an email to the Orange County Register.

The suspect has not yet been identified. NBC News reports that the teacher has been arrested.