Within two to three days of the transplant, most patients are “symptom free …They get their lives back,” said Michael Edmond, an infectious disease specialist at Virginia Commonwealth University. It’s about as close to a miracle cure as medicine offers.

Yet access to fecal transplants has proven challenging. As recently as 2013, Amy Barto, a gastroenterologist at the Lahey Clinic in Massachusetts, said her patients had to find their own stool donors, whom the clinic would screen individually. On the day of the procedure, the donor had to provide a fresh stool sample, which Barto said she personally mixed using a blender from Target and transplanted into the patient’s colon. “It was embarrassing and stressful for patients to find their own donors, and expensive to have them screened,” she said. “I did about 100 procedures with the blender, and it was not efficient.”

In 2013, Smith and a college friend, James Burgess, decided to start a not-for-profit stool bank, called OpenBiome, providing pre-screened, frozen samples to doctors and hospitals. Smith’s MIT advisor, Eric Alm, offered guidance as well as a corner of his laboratory, and the team began to recruit donors, mainly among MIT and Harvard researchers. “When OpenBiome was established, my quality of life went through the roof,” Barto said. More importantly, access to the procedure “just blossomed.” More doctors were willing to get involved and patients were able to able to get the procedure more quickly, with fewer barriers and less expense.

One such patient was Natalie Jamil. In April, Jamil, then 25, discovered that a root canal she had had for years was badly infected. Her dentist extracted the tooth, treating her with antibiotics before and after the procedure. A week after she stopped taking the drug, however, she began to vomit and developed severe diarrhea, cramping, and pain in her joints. Jamil had recently taken a job as a secretary in Washington D.C., but “it became impossible to get to work, and I was asked to resign,” she said. “I was left with no job, no health insurance, and no tooth.”

Searching the web in desperation, she found Edmond. “I had lost over 25 pounds in two months,” Jamil said. “I was ready to do anything.”

In June, Jamil received the treatment using frozen stool from OpenBiome. Edmond administered the sample through a tube that threaded in through her nose and down into her small intestine. “It was like the flicker of a light,” she said. “The next day I was back on my feet. My stomach was calm. I wasn’t having diarrhea. It was like magic.”

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OpenBiome is similar in some ways to a blood bank, which also collects, screens, and distributes biological material. Early on, though, it became clear that the group faced different challenges in recruiting donors and testing samples. For one thing, few applicants qualified: Anyone who had had a gastrointestinal disease, recently used antibiotics, or traveled to any country with a risk of waterborne illness was rejected, even before their stool was analyzed for pathogens. It was sometimes awkward turning away MIT colleagues who wanted to contribute stool, Smith said, but “it helped to say, ‘Hey, I’m not eligible either.’”(Smith’s brother lives in Singapore and he visits there each year.) OpenBiome tests stool for an extensive list of pathogens, including HIV, hepatitis, and syphilis, which can be transmitted through bodily fluid. But they also screen for disorders, from obesity to metabolic syndrome to autoimmune diseases, that are not traditionally viewed as contagious but have been at least correlated with disturbances in gut bacteria. At a blood bank, no one worries that transfusions might make patients obese.

Rather than casting its net wide for donors, OpenBiome cultivates a small group of stalwart contributors. That way, the cost of testing, which can be roughly $1500 per donor, is spread over many patients and treatments. Contributors in this model make a major commitment. They are required to bring in samples within an hour of passage, since the bacterial composition of stool changes rapidly with exposure to air. “We have one guy who brings his samples in on [Boston’s T train],” Smith said. But for the most part, donors are students who live or work close by. When the project moved from Alm’s lab at MIT, this spring, to a new location near Tufts University, OpenBiome sought out a new cohort of dedicated graduate students. Their constancy also means the group can reassure doctors that the individual whose stool they are receiving has already cured numerous cases of recurrent C. diff—and has not caused new infections in any recipients.