If the Walter Reed National Military Medical Center told you that you tested negative for HIV in October, you might want to get in touch. The facility in Bethesda, Md., says a mistake occurred late in the month, when two blood samples out of 150 were mixed up. A sample that tested positive was mislabeled with the wrong person's name; that patient later determined he or she was not actually infected. So the medical center, the military's "flagship hospital," is now trying to figure out who the positive sample actually belonged to, the New York Times reports.
Officials narrowed the group down to the 72 people with the same blood type as the sample and sent them certified letters last month; 63 people responded, and 50 of them have gotten new blood tests. But as for the other nine people... "Email, phone, letters: We are trying every way we can to get in touch with those folks," says the hospital spokesperson. As for how the mistake happened, that's under investigation. The sample in question was taken on Oct. 23.