PERFORMANCE OF THE AMPLICOR HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PCR AND ANALYSIS OF SPECIMENS WITH FALSE-NEGATIVE RESULTS

Over a 4-year period, the Roche Amplicor kit was used in a United King dom reference laboratory for the detection or confirmation of human im munodeficiency virus (HIV) type 1 infection, particularly in infants b orn to HIV-infected mothers, Of 408 specimens from adults and older ch ildren tested, the 122 seronegative specimens were all Amplicor negati ve, Of the 286 seropositive specimens, 268 were Amplicor positive. On the basis of these results, the Amplicor assay has a specificity of 10 0% and a sensitivity of 93.7%. In addition, for 247 specimens from inf ants and young children serological results may not have been diagnost ic because of placental transfer of maternal antibodies. Forty-eight w ere Amplicor positive, and of the 199 Amplicor-negative specimens, 19 were assumed to be false negative on the basis of clinical data, serol ogical markers (including p24 antigen), and/or results for previous or follow-up specimens, This represents a sensitivity of 75% for the Amp licor test for specimens from patients under 2 years of age, Of these 37 false-negative specimens plus 2 specimens from other laboratories, 31 could be characterized by amplifying extracted material from them b y an in-house nested gag PCR spanning the Amplicor target region, The amplicons were sequenced and found to represent subtypes A (35.5%), B (22.6%), C (22,6%), D (16.1%), and G (3.2%), False-negative results by the Amplicor assay may be ascribed to low-target copy number, the phy sical behavior of one primer (SK462), and sequence variation in the ta rget region of the other primer (SK431).