Four years ago, Natalie Gurvich developed a strange reaction to antibiotics she’d been prescribed for strep throat: horrible stomach problems, no matter what she ate, up to 20 times a day.

The diagnosis: Clostridium difficile, known as C. diff. It’s a bacterial infection that affects as many as half a million people in the U.S. each year, causing almost 30,000 deaths.

After a fecal microbiota transplantation at NYU’s Langone Medical Center it took about two only months to check properly that she hasn’t felt any symptoms of C. diff.