Epidemiologic and evolutionary trends of HIV-1 CRF31_BC-related strains in southern Brazil

Background: To evaluate the impact of HIV-1 CRF31_BC in the southern Brazilian HIV epidemic. Methods: Blood plasma from 284 patients was collected from July 2002 to January 2003 at 2 reference HIV/AIDS centers in southern Brazil. Viral protease and reverse transcriptase (RT) genomic regions were amplified by RT polymerase chain reaction, sequenced, and subtyped. Evolutionary analyses were performed to estimate the CRF31_BC most recent common ancestor and its population growth rate with BEAST version 1.3. Results: CRF31_BC was responsible for 7.4% of infections. The average time of HIV diagnosis and the proportion of patients on antiretroviral treatment were shorter for CRF31_BC and subtype C than for subtype B. CRF31_BC was found as early as in 1990 in the Brazilian epidemic. Evolutionary analysis of CRF31_BC revealed that it appeared immediately after the introduction of subtype C in Brazil and has been growing at a similar rate as subtype C. Conclusions: CRF31_BC plays an important role in the HIV epidemic of southern Brazil, and its prevalence has increased throughout the years. This circulating recombinant form corresponds to approximately 25% of total HIV isolates in this region in 2004. Understanding the cause of this spread is important for public health strategies in Brazil and in Latin America.