The Centers for Disease Control and Prevention (CDC) conducted a test to detect the p24 antigen in the blood of a frequent plasma donor. This test, now considered more reliable than the standard HIV-antibody test, showed traces of the virus in the blood of a Utah man who had tested negative following his wife's diagnosis of AIDS. The man continued to donate plasma from 1994 through August 1995, when he developed Pneumocystis carinii pneumonia (PCP), an AIDS-defining illness. The man's plasma was not recalled because it had been heat-treated to inactivate the virus. Whole-blood donations are not treated. Of the 12 million units of blood donated annually in the U.S., an estimated 32 to 49 donations of whole blood per year carry the virus.