Comparative performance of three viral load assays on human immunodeficiency virus type 1 (HIV-1) isolates representing group M (subtypes A to G) andgroup O: LCx HIV RNA Quantitative, AMPLICOR HIV-1 MONITOR version 1.5, andQuantiplex HIV-1 RNA version 3.0

The performance of the LCx HIV RNA Quantitative (LCx HIV), AMPLICOR HIV-1 M ONITOR version 1.5 (MONITOR v1.5), and Quantiplex HIV-1 RNA version 3.0 (bD NA v3.0) viral load assays aas evaluated with 39 viral isolates (3 A, 7 B, 6 C, 4 D, 8 E, 4 F, 1 G, 4 mosaic, and 2 group O). Quantitation across the assay dynamic ranges was assessed using serial fivefold dilutions of the vi ruses. In addition, sequences of gag-encoded p24 (gag p24),pol-encoded inte grase, and env-encoded gp41 were analyzed to assign group and subtype and t o assess nucleotide mismatches at primer and probe binding sites. For group M isolates, quantification was highly correlated among all three assays. I n contrast, only the LCx HN assay reliably quantified group O isolates. The bDNA v3.0 assay detected hut consistently underquantified group O viruses, whereas the MONITOR v1.5 test failed to detect group O viruses. Analysis o f target regions revealed fewer primer or probe mismatches in the LCx HIV a ssay than in the MONITOR v1.5 test. Consistent with the high level of nucle otide conservation is the ability of the LCx HIV assay to quantify efficien tly human immunodeficiency virus type 1 group M and the genetically diverse group O.