Gregory Spoor got the distressing news about his wife on the morning of Jan. 16 while standing outside her room in the intensive care unit at Northwestern Memorial Hospital in Chicago. The doctor explained that Stephanie Spoor, 64, had contracted a “rare, very rare, fungus.”

The physician said the fungus was called Candida auris, and it appeared to have entered her bloodstream through a catheter or other intravenous line during her treatment. Mr. Spoor sent a text to the couple’s four children.

“Hey guys, I’m very sorry to do this via text but you need to know and not fair to wait until all of us are together,” he wrote. “The fungus mom has is the worst possible and can be terminal.”

He added: “It is a day to day issue so I don’t have any more answers or info at this time.”

Mr. Spoor, 67, an executive at a plumbing equipment company, wasn’t the only one with few answers. C. auris, a germ that typically is resistant to major antifungal medications, has been quietly confounding doctors, hospitals and infectious disease scientists around the world.