Frequency of CXCR4-using viruses in primary HIV-1 infections using ultra-deep pyrosequencing.

We used ultra-deep pyrosequencing and the Toulouse Tropism Test phenotypic assay to determine the prevalence of CXCR4-using viruses in 21 patients with primary HIV-1 infections. We found X4-containing virus populations in 9% of patients by ultra-deep pyrosequencing using position-specific scoring matrices (PSSM(X4/R5)) or geno2pheno(5.75) and in 14% using the combined 11/25 and net charge rule. The phenotypic assay identified 9% of CXCR4-using viruses. This confirms that R5 viruses are predominant in primary HIV-1 infections.