“You can’t 100% prove that someone doesn’t have something because we don’t have perfect tests. So we try and put together a combination of their exposures, their clinical history, testing, radiology like a CT-scan of the lung of the donor, which was done and didn’t show anything that looked like COVID,” Dr. Daniel Kaul, the director of the Transplant Infectious Disease Service at the University Michigan who helped write the study, told the Detroit Free Press.