Antibiotics didn’t cure their infections. Fecal bacteria did.

Until now, there has never been a clinical trial conducted in more than one medical center that has investigated so-called fecal transplants as a first therapy for C. difficile infections, said Dr. Michael Bretthauer, a gastroenterologist at the University of Oslo and lead author of the new study.

The Food and Drug Administration permits fecal transplants and professional societies endorse them, but only a last resort for treating C. difficile infections after antibiotics have failed, said Dr. Alexander Khoruts, a gastroenterologist at the University of Minnesota.

“The F.D.A. and all the professional societies are in full agreement on this point,” he said.