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Background:  Infection with subtype-C HIV virus is becoming more common worldwide. Therefore, new versions of different assays have been developed to suit measurements of viral load in non-subtype-B infected patients. Several studies previously reported viral load underestimation as measured by NASBA assay, compared to Amplicor HIV-1 Monitor Assay Version 1.5. The present study was designed to evaluate the performance of a newer version of the NASBA assay in subtype-C infected patients.

Methods:  The performances of Amplicor HIV-1 Monitor Assay Version 1.5, and of real-time nucleic acid sequence-based amplification HIV-1 assay (NucliSens EasyQ) were evaluated in 28 HIV subtype-C-infected patients; 20 HIV-1 subtype-B-infected patients served as a control group. Blood samples were prospectively collected from patients in both groups and each sample was tested by both assays. Results of the Amplicor assay were multiplied by a factor of 0.51 in order to convert copies/mL into international units (IU). The log converted results were compared using a paired, 2-tailed student’s t-test.

Results:  Viral load results from the Amplicor and EasyQ assays of each patient were compared. The discrepancy between the 2 assays was highly significant for subtype C (p = 0.01) but non-significant for subtype B (p = 0.77). Discordant results (> 0.5 log difference) between the 2 assays were detected in 42% (12 of 28) of subtype C samples, compared with 15% (3 of 20) of subtype B samples. A discordant result of greater than one log was obtained In 17% (5 of 28) and 10% (2 of 20) of subtype-C and subtype-B-infected patients respectively. In subtype C, the mean viral load as measured by the Amplicor assay was 137,880 IU (range 232 to1,421,000), whereas a mean of 121,132 IU (range 25 to 2,500,000) was measured using the NucliSens EasyQ assay. In subtype-B samples, the mean viral load was 143,932 IU (range 232 to 1,397,800) using the Amplicor assay, and 34,500 IU (range 25 to 3,100,000) using the NucliSens EasyQ assay.

Conclusions:  In our study, a statistically significant difference was found between the results of viral load measurements obtained using the NucliSens EasyQ assay and those obtained by Amplicor HIV-1 Monitor assay Version 1.5, in subtype-C-infected patients. This difference may have significant bearing on patient care.

Keywords: Subtype C; NucliSens EasyQ ; Amplicor HIV-1 Monitor assay Version 1.5