Background:  The study of HIV recent seroconverters provides critical information about the main characteristics of the epidemic in a given region. Knowledge about the predominant HIV subtypes, proportion of drug-resistant strains, and HIV co-receptor usage of viruses currently transmitted is crucial for the optimal design of first line therapies.

Methods:  All consecutive recent HIV seroconverters (<12 months from exposure) seen since January 1997 to September 2006 at 15 different hospitals distributed across Spain were examined. Major drug resistance mutations (International AIDS Society-USA list updated in September 2006), HIV subtype and estimation of co-receptor usage using V3 loop amino acid sequences were performed.

Results:  A total of 358 recent HIV-1 seroconverters were identified. Median time from initial HIV exposure was 7 months; 69.5% were men who have sex with men (MSM). At the time of first diagnosis, median plasma HIV RNA was 4.7 log and median CD4 count 569 cell/μL. Overall, 12.6% of patients carried viruses with drug resistance mutations. They were 9.9% for nucleoside reverse transcriptase inhibitors (NRTI), 4.5% for non-NRTI (NNRTI), and 3.4% for protease inhibitors (PI). While a significant decline in the transmission of drug-resistant viruses was seen comparing the periods 1997-1999 and 2000-2001 (29% vs 5.3%, p <0.001), a rebound was seen in the period 2002-2004 (10.7%) and particularly in 2005-2006 (13.2%). Moreover, an increased transmission of viruses with resistance to NNRTI and PI occurred (5.4% and 6.2%, respectively). Furthermore, within the last 3 years, 5 patients have acquired viruses containing resistance mutations to all the 3 drug families—41L (5), 74V (1), 118I (3), 210W (3), 215N/S/D (5), 103N (5), 46L (1), 82A/T (2), and 90M (3). A total of 24 individuals (6.4%) carried non-B subtypes (8 CRF14_BG, 4 CRF03_AG, 3 CRF12_BF, 3 C, 3 G, 2 F, and 1 A). Interestingly, they only began to be recognized since 2001. X4 viruses, either as pure or dual/mixed population, were recognized in 15.3%. Distinct HIV tropism (X4 vs R5) was not associated with plasma HIV RNA (4.5 vs 4.4 log copies/mL), nor CD4 counts (594 vs 540 cells/mL), nor with drug-resistance mutations.

Conclusions:  A significant proportion (13.2%) of recent HIV-1 seroconverters in 2005-2006 harbor drug-resistance mutations, which represents an increase with respect to prior years. Moreover, PI-resistant and multidrug-resistant viruses have become more frequent in recent years. The presence of X4 viruses does not seem to be associated with transmission of drug-resistance mutations.