The conclusion of a survey of DNA fragments in blood circulating in humans conducted by Stanford researchers has found that 99% of the microbes in our bodies have never been seen, classified, or named. This conclusion was found somewhat accidentally when Stephen Quake, Stanford Professor of Bioengineering and Applied Physics, along with his lab members, examined blood samples from organ transplant recipients in order to see whether or not the transplants had been rejected by the patient's immune system. Of all of the DNA examined, 99% of the microbes did not match anything in the existing genetic databases. 

"What this does is it arms infectious disease doctors with a whole set of new bugs to track and see if they're associated with disease," Quake said. "That's going to be a whole other chapter of work for people to do".