SYPHILIS SEROLOGY IN HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION - EVIDENCE FOR FALSE-NEGATIVE FLUORESCENT TREPONEMAL TESTING

Injection drug users were assessed serologically for human immunodefic iency virus infection and syphilis every 6 months, Treatment histories were reviewed for any high-titer biologic false-positive (BFP) reacto rs, that is, persons with rapid plasma reagin (RPR) titers greater tha n or equal to 1:4 and negative results for fluorescent treponemal anti body absorption (FTA-ABS) tests, Selected sera were analyzed further b y immunoblotting for the presence of antibodies reactive with specific Treponema pallidum antigens, Of 112 BFP reactors, 35 (31%) had at lea st one RPR test reactive at a dilution >1:8 while the FTA-ABS test rem ained nonreactive. Five reactors (4.5%) converted from nonreactive to reactive by FTA-ABS test; 4 (3.6%) were reactive by FTA-ABS tests but later became nonreactive, Antibodies to T. pallidum membrane antigens were detected in some samples that were persistently nonreactive by FT A-ABS test, Serologic patterns over time, along with very high-titer B FP reactions and reactivity with T. pallidum-specific antigens, sugges t that some BFP reactions may represent FTA-negative syphilis.