USA regional differences in low HIV viral loads: Management or response to HAART?

P. Heseltine*¹, R. Kagan¹, E. Koski², H. Hamdan¹, K. Chen¹, W. Meyer⁴, T. McCormick³, A. Maddo² and M. Lewinski¹. ¹Quest Diagnostics Nichols Institute, San Juan Capistrano  CA 92690; ²Quest Diagnostics, Advanced Diagnostics IT, Lyndhurst, NJ 07071; ³Quest Diagnostics, Teterboro NJ 07608; ⁴Quest Diagnostics, Baltimore MD 21227(USA).

Background: Suppression of HIV viral load by HAART to <50 copies/mL has been shown to correlate with favorable clinical outcome. We investigated the geographic distribution of ordering patterns and results of HIV-1 RNA assays performed by UltraSensitive RT-PCR, Standard RT-PCR or branched DNA across a large diagnostic reference laboratory system. Material and Methods: Clinical samples submitted for the HIV-1 RNA quantitative assays AMPLICOR® HIV-1 MONITOR UltraSensitive RT-PCR assay version 1.0 (Roche Diagnostics) and VERSANT® HIV-1 RNA 3.0 branched DNA assay (Bayer Corporation), performed at six Quest Diagnostics reference laboratories were reviewed.  Data were available for 168,383 UltraSensitive PCR results and for 103,556 bDNA results collected over a 16-month period from Oct. 2001 to Jan. 2003. Results: Undetectable viral loads of <50 cp/mL were found in 46.8% usPCR and 38.3% by bDNA.  The overall frequency of low-level viremia (50 - 400 cp/mL) was 24.8% by usPCR and 11.2% by bDNA.  These proportions remained relatively constant over a 16-month period by region.  While the regional distribution of test orders closely followed the CDC case rates for the 10 states with the highest cumulative incidences of AIDS, the geographic data showed a higher proportion of patients in Massachusetts with undetectable viral loads by usPCR (52.6% <50 cp/mL) than in Florida (33.0% <50 cp/mL). Conclusion: Regional variations in the numbers of patients with low positive viral load are not fully explained by assay method or ordering practices. Regional resistance data (to be presented) may also not explain the differences in outcome. These controlled data provide an opportunity to consider the impact on successful HAART of regional prescribing and adherence practices.