A few years ago, Hirsch saw a man in his 40s—an otherwise healthy runner who had developed a common respiratory infection. He was prescribed an antibiotic, and three days later he began experiencing severe diarrhea caused by a C. diff infection. Eventually he developed a complication of C. diff known as toxic megacolon, in which the colon swells and, in some patients, ruptures.

“Within 48 hours, he was on the table of an operating room having his colon removed,” Hirsch said. “He went from a healthy, jogging, middle-aged normal guy to an individual who is fated to shit out of his side for the rest of his life into a colostomy bag.”

More than 250,000 Americans each year require hospitalization for C. diff infections, and roughly 14,000 die from it, according to the CDC. In its recent report on drug resistance, the CDC classified C. diff as an “urgent” threat.

C. diff infections are often sparked when a person with an unrelated ailment takes a round of antibiotics, which kill off the gut’s “good” bacteria in the process. But Hirsch said he sees the bacteria even in patients who haven’t used antibiotics recently.

To him, this means C. diff is generating hearty, impossible-to-kill spores that allow it to jump from person to person, including within hospitals.

To make matters worse, certain strains of C. diff have evolved to withstand even the heaviest bombardment by drugs. Until recently, it could be treated with antibiotics, but in the late 1990s, the bug morphed and became much harder to eliminate.

“We knew we had a horrific problem,“ Mark Miller, former head of infectious diseases at the Jewish General Hospital in Montreal and a doctor who helped document C. diff’s transformation, told a Canadian news service. “We knew it was a bad C. diff, a more virulent C. diff.”

Increasingly, doctors are finding that their last remaining weapon is the bacteria from a healthy person’s bowels.

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Fecal transplants aren’t a new therapy—the first was performed in 1958—but it’s still a relatively rare procedure because it’s logistically and, well, cognitively unappealing. Only about 20 doctors in the U.S. perform the procedure, and just 500 to 700 patients have received the transplants.

However, the rise of this more tenacious C. diff strain is pushing both patients and doctors to get over their fecal fears. In January, a study in the New England Journal of Medicine found that a far higher percentage of patients infected with C. diff recovered among a group being given an enema containing the stool of a healthy donor than did among those who were treated with antibiotics. Fecal transplants have been shown in that and other studies to cure 90 percent of C. diff infections within a few days.

But the procedure is far from simple. In clinics, they’re usually administered through a colonoscopy-type procedure, which is uncomfortable for sick and elderly patients, or through a tube stuck down the patient’s nose and into the stomach, which only exacerbates the patient’s natural feeling of disgust.