The researchers collected poop samples from four healthy donors who hadn’t taken antibiotics for at least six months. Their blood was screened for HIV, hepatitis A, B and C, and a bacterium that causes syphilis. In addition, their feces were tested for various intestinal pathogens. Four weeks after their donations, they were screened again for HIV and hepatitis B and C to be sure nothing was missed the first time around.

The donated stool was placed in a blender and mixed with saline, then strained to remove large particles. The remaining “slurry” was concentrated and packed into capsules that contained about 1.6 grams of fecal matter apiece. Then the pills were kept frozen at a chilly 112 degrees below zero.

A total of 20 patients received the pills between July 2013 and January 2014. The patients, whose ages ranged from 11 to 89, had suffered at least three bouts of mild to moderate CDI or had at least two episodes that were severe enough to send them to a hospital. Before they tried the frozen pills, they were having diarrhea up to 30 times a day.