A hospital in Pittsburgh is investigating whether the deaths of two patients are linked to infections from mold they may have contracted while in an intensive care unit.

UPMC Presbyterian said this week that the cardiothoracic intensive care unit was closed Sept. 3 for an environmental cleanup after mold was discovered.

Eighteen patients were relocated and one lung transplant patient became ill with a mold infection on his lung tissue.

Officials said the two heart transplant patients who died had contracted fungal infections and stayed in the unit. One was infected in October 2014 after doctors discovered a mold infection on the patient's left leg. The other was infected in June after mold was detected on the buttocks.

The type of mold found in the two heart transplant patients was different than that of the lung transplant patient.

Tami Minnier, UPMC's quality control chief, said doctors at the hospital don't know if the infections played a role in their deaths. A review of patient records found their infections started nearly a year ago.

Minnier said a total of 56 patients stayed in the room over the previous year.

She said that UPMC is currently unaware of any other infections. Mold has not been located in any other part of the hospital.

"It's just heartbreaking," Minnier said. "I can't tell you how many hours we have already spent trying to understand it. I still feel like I am navigating a very active investigation."