LAKE FOREST – County public health experts said Wednesday they’ve pinpointed the source of skin irritations that have affected dozens of students and staff members at Lake Forest Elementary: blood-feeding mites lurking on at least one of the school’s playgrounds.

Mite specialist Steve Bennett, who has been assisting Orange County Vector and Mosquito Control to solve the mystery, collected wood chips this week from three of the school’s playgrounds. On Wednesday, he found evidence of 25 mites in one of the samples — more specifically mites from the Mesostigmata order, which are known to be blood-feeding as opposed to chiggers, which feed on surface skin material, vector control spokesman Jared Dever said.

“This was the smoking gun we were looking for,” Dever said. “Everything about this mite fits the bill for what has caused these types of injuries.”

Bennett took samples of wood chips after being told they were added around the time the bites started occurring. Wood chip samples were taken from highly used playground areas, including under slides.

“Kids could be falling down in these areas and have a high exposure to these mites,” Dever said.

For those students and staff affected by bites and skin irritation, Dever recommended consulting a physician and including information on what type of mite likely was to blame.

“The type of mite we’re dealing with causes a different type of irritation,” he said, “but the physician should be able to provide the best course of relief.”

Evidence of the mites came from the playground closest to The Learning Center, the school’s after-school program, he added.

To solve the mystery, Bennett placed wood chips in berlese funnels, then used a light source and a capture jar to extract the samples.

“We haven’t used berlese funnels here in probably 15 years,” Dever said. “It’s incredibly hard to find mites on wood chips because of their shapes, so we placed them in the traps.”

Kristin Faller, mother of a second-grade Lake Forest Elementary student, said knowing the likely source of the her child’s ailment is a relief.

“Now it’s not just some unknown out there,” she said. “Hopefully, with them having the area roped off for so long, the chance of it coming home is slim.”

In a letter sent to parents before Bennett’s findings Wednesday, Principal Richard Rodriguez said the fields in which the playgrounds are located would remain closed for further testing.

Dever said removal of the wood chips from play areas would be the best course of action. He also said it’s possible the mites have moved around the campus, but it’s up to school officials to decide whether it wants to do further surveillance.

School officials first informed the Saddleback Valley Unified School District of the skin irritations on Sept. 15, and the district later reported 30 students and 10 staff members had been affected. The source of the problem initially was said to be around fields near the after school program, which uses the portable buildings on the north side of the campus.

SVUSD hired Safety First – a pest-control company – to spray pesticides on the campus on the weekend of Sept. 24-25. Vector control laid traps for chiggers and mites in the following days, and came up empty.

Parents asked questions of district staff and Dever at a Parent-Teacher Organization meeting Sept. 28 and asked whether the campus was safe for children or not. The school did not close down because of the investigation.

Contact the writer: npercy@scng.com