Seattle Children's hospital has reopened 14 of its operating rooms after one patient died and five others developed an infection from mold following surgical procedures over the last two years.

The hospital closed the operating rooms in May after routine testing detected aspergillus in several ORs and in equipment storage areas. The closure resulted in roughly 1,000 surgeries being moved to other hospitals, according to NBC affiliate King5 News in Seattle.

The operating rooms reopened Thursday after the hospital deep-cleaned the rooms, upgraded its air handling and purification systems, and installed a new humidification system.

"We want to reiterate how sorry we are for the impact that this air quality issue has had on our patients and families and that we are doing everything we can to maintain a safe environment for our patients," hospital Chief Medical Officer Dr. Mark Del Beccaro said at a news conference. "That is our highest priority."

Lindsay Kurs, a spokesperson for the hospital, said three patients developed aspergillus surgical site infections in 2018 and one of them died. Another three patients developed infections this year, Kurs said.

"We are deeply saddened that one of these patients died," she said in a statement. "Out of respect for our patients’ privacy, we cannot share additional details."

Aspergillus is a fungus whose spores are present in the air, but does not normally cause illness, according to the aspergillus & aspergillosis Website. The fungus can cause disease in people who have weakened immune systems, damaged lungs or have allergies, the website states.

Kurs said the risk of other patients developing an infection from the mold "is very low."

Seattle Children's first became aware of the aspergillus last year, according to the Seattle Times. It was found again May 18, prompting the hospital to close four operating rooms, King5 News reported.

Del Beccaro said the hospital hired an outside company to investigate and alerted the Department of Health on May 20. An additional 10 operating rooms were closed May 24 and as a precaution, Seattle Children's sent letters to about 3,000 families of patients who had operations and may have been exposed.

Del Beccaro said the "overwhelming majority of those patients" had little to no risk of being exposed to aspergillus.