Background:  Increasing access to the benefits of HAART requires that healthcare providers can adequately monitor response to therapy. In developed countries, therapy is initiated and monitored by measuring HIV-1 viral load by quantitative RT-PCR. However, this method is expensive and impractical for use in developing countries. An alternative, inexpensive assay is the signal-amplification-boosted p24 assay, which we evaluated to determine its utility in measuring viral load compared to HIV-1 RNA in HIV-infected individuals in Africa.

Methods:  Archived serum samples of 290 seroprevalent individuals from Rakai, Uganda, who were infected with HIV-1 subtypes A, D, and A/D recombinants were evaluated. Levels of HIV-1 RNA were quantified by RT-PCR (Roche Amplicor HIV-1 Monitor 1.5 assay). HIV-1 p24 antigen was quantified by the HIV-1 p24 Core Profile ELISA boosted by the ELAST ELISA Amplification System (NEN Life Science Products). We evaluated the correlation between HIV-1 RNA and p24 antigen levels by the Spearman correlation coefficient. For 272 participants followed for 30 months, Cox proportional hazards models assessed progression to death as predicted by HIV-1 RNA and p24 antigen levels.

Results:  The mean age of participants was 33.2 years (SD, 9.2) and 65.8% were female. The mean and median serum levels of HIV-1 RNA were 275,452 copies/ml (SD, 614,516 copies/ml) and 37,702 copies/ml (IQR, 5,271–166,830), respectively. The mean p24 was 5.8 pg/ml (SD, 18.6); the median p24 was 0.8 pg/ml (IQR, 0.1–2.0). When log-transformed values were used, the median log₁₀ HIV-1 RNA was 4.6 log₁₀ copies/ml (IQR, 3.7–5.2). The median log₁₀ p24 was -0.1 log₁₀ pg/ml (IQR, -1.0–0.3). The p24 antigen did not correlate well with HIV-1 RNA. Spearman correlation coefficient was 0.37 (p-value < 0.0001). HIV-1 RNA greater that 55,000 copies/ml strongly predicted progression to death with hazards ratio of 7.5 (95% CI, 2.6–21.5). A p24 antigen level greater than 2.0 pg/ml (75^th percentile) predicted progression to death with hazards ratio of 2.2 (95% CI, 1.1–4.5).

Conclusions:  This analysis of African samples illustrates a weak correlation between the p24 antigen assay and HIV-1 RNA. This suggests that further development is required to improve the application of this technique in regions where non-B viral subtypes predominate. Further studies are required to confirm the predictive value of the p24 antigen assay in Africa before it can be used for the initiation and monitoring of HAART.