But it isn't some kind of killer mold. It's a household kind -- plain old indoor mold.
It doesn't threaten the general population, or patients and staff with normal immune systems at the University of Pittsburgh Medical Center.
But UPMC said it believes the mold may have contributed to the deaths of organ transplant patients, including one who died Thursday at UPMC Montefiore.
Two other patients died in October and in June at UPMC Presbyterian, CNN affiliate WTAE-TV reported.
And UPMC said another patient is deathly ill with the same kind of mold infection.
Compromised immune system
People usually have plenty of contact with such molds, and nothing happens, UPMC said.
"The mold that causes infections like this is common in the environment and is not a risk to anyone except those who are most severely immunocompromised," it said in a statement
without giving the scientific name of the mold.
That latter group would include people who have received donor organs. Fungal infections are on the list of known health risks after transplant surgery, the Centers for Disease Control and Prevention said.
The drugs that prevent a patient from rejecting the new organ depress the immune system, opening the patient up to infection risks about which hardly anyone else would have to worry.
But these infections unfortunately pop up after a transplant, a CDC study shows.
Often the infected patient dies.
Report: Two patients who died had same room
WTAE reported that the first two patients who died stayed in the same room in the cardiothoracic ICU at UPMC Presbyterian.
Mold deposits were found in toilets and behind walls in the unit, and UPMC closed it temporarily and sent in a team to assess and clean the area. UPMC doesn't know how the mold got there, the TV station reported.
The air quality at UPMC Montefiore has also been checked for mold. "We have not received any concerning results," UPMC said in a statement. Still, it has replaced all of its germ-catching air filters.
And it is sending in a disinfecting robot to its ICUs to zap any germs with ultraviolet light.
Nicknamed "Violet," it looks like R2-D2 from "Star Wars" with an extendable neck and a camera flash on steroids.
All transplant patients at UPMC Presbyterian and UPMC Montefiore will receive an antifungal medication, even though they are not infected. "This prophylactic treatment is intended to protect them until we find and fix the source of this problem," a statement said.
Fungal infections may be more common in patients receiving small bowel sections, lungs, livers and hearts in descending order, the CDC said. Fungal infections also often cause a rash.
The first patient to die received a lung, as did the patient who recently has been strongly afflicted by the fungus. The patient who died Thursday had received a liver.
But that patient was neither exposed to the now-closed ICU nor to the other patient who is currently infected, UPMC said. It is still trying to figure out how that case might be related to the others.
The patient who died this week also had a rash that appeared to be fungal, UPMC said. And preliminary tests indicate the infection was in line with the other cases.
UPMC said it is working with independent experts, county and state health agencies and the CDC to track down the problem.