About 10 patients at an Oregon hospital - and possibly more - suffered burns because staff didn't replace filters on lights in three operating rooms, officials at the medical center said Wednesday. 

Staff at Silverton Hospital changed diffusers on the halogen lights in September 2013 but left out the filters, officials said. The first cases of skin burns came to the hospital's attention the following June, said Ray Willey, director of quality and risk services. A hospital investigation pinpointed the cause five months later in November.

As many as 2,100 surgery patients who underwent procedures in the operating rooms during the 14-month period may have been at risk, Willey said.

Halogen lamps emit ultraviolet light and must have filters, according to a report from the National Institutes of Health. The filter is often incorporated into the bulb's glass, but some lamps require separate filters.

It took several months to figure out the cause of the burns, Willey said, because the hospital initially looked at more common culprits: solutions used to prep skin before surgery, bandages or dressings used after surgery, and cautery devices used to stop bleeding during surgery.

When none of those turned out to be the cause, a surgical team member recalled maintenance had been done on the lights, Willey said.

Operating room staff had routinely replaced light bulbs in the operating rooms, he said, but they had not performed equipment maintenance such as changing diffusers.

"This was a bit unusual," Willey said. "They had not realized the complexity of changing the diffusers."

Fewer than 10 patients have contacted the hospital about burns thus far. Their injuries range from mild burns to severe "thick skin burns."

None of the patients has been permanently disfigured, Willey said. In the most extreme known cases, patients will have permanent redness on the part of their skin that was exposed to the light.

Because patients are draped during surgery, he said, only isolated patches of skin where the light was focused were burned.

The hospital has notified the Oregon Safety Patient Commission and will soon submit a formal report.

No one has been fired because "it was a system issue, not an individual issue," Willey said.

The hospital has replaced the halogen lights with lamps that use light-emitting diodes, or LEDs, and it has changed procedures for medical equipment maintenance. Staff must now notify the hospital's engineering department or the equipment's vendor to do any kind of maintenance.

Hospital officials are also working to find other affected patients and to provide compensation to those who experienced burns.