Emergence of X4 usage among HIV-1 subtype C: evidence for an evolving epidemic in South Africa.

This study investigated the genotype and phenotype of HIV-1 isolates of 20 South African AIDS patients. We found the highest percentage of CXCR4 usage among primary isolates, in which 30% efficiently utilized CXCR4 and exhibited the syncytium-inducing phenotype. Phylogenetic analysis of env confirmed that 19 of the 20 were subtype C, and syncytium-inducing viruses had genetic changes in the V3 loop, characteristic of CXCR4 usage. Results imply that the frequency of CXCR4-utilizing subtype C is increasing with time.