Robert Badura1, Helena Cortes Martins2, Rita Sobral2, Emilia Valadas3, Ricardo Miguel2, Maria Teresa Paixão2, Francisco Antunes1,3. 1Serviço de Doenças Infecciosas, Hospital Santa Maria, Lisboa, 2Laboratório de Virologia, Instituto Nacional Dr. Ricardo Jorge, Lisboa, 3Faculdade de Medicina de Lisboa (Portugal).

Background: Resistance testing of therapeutic naive patients with chronic HIV infection has a doubtful value because it might fail to detect the minor subpopulation responsible for eventual pre-existing resistance and therefore likely to underestimate its real extend. Considering the time HAART has been used now one would expect to see an increase of resistant virus transmission. The vast majority of HIV-infection though is discovered in their chronic carrier stage or even when presenting AIDS – defining illnesses. In aim to characterize this cohort in respect to eventual resistance detectable we proposed a prospective pilot study. Material and Methods: These results here are the first preliminary evaluation of the first twenty-five patients, being the final goal to follow 100 naïve chronic infected patients with indication to initiate therapy. From this study were excluded patients with obvious low adherence, an active drug addiction problem or adverse drug reactions. After obtained consent, HIV resistance testing was proceeded simultaneously on patient’s first laboratory evaluation prior to any therapy. Ability to suppress retroviral proliferation will be compared to the results from HIV resistance testing at 6, 12 and 18 month after therapy onset. Genotypic resistance was assessed with Viro Seq TM HIV-1 Genotyping system. Results: We found that 18 patients had a non-B genotype (7 G, 1 F, 9 Recombinants) and 7 with genotype B. This corresponds with other surveys, demonstrating a relative high prevalence of non-B genotype in Portugal. Two patients had demonstrable resistance, one to nelfinavir and the other to nevirapine. All patients had mutations in the protease-gene originating in potential resistance to nelfinavir (3) and saquinavir and lopinavir (1). Intermediate resistance to saquinavir was shown in another case, probably reflecting the increased use of protease inhibitor in the last couple of years. Conclusion: Albeit considering this very limited number of patients so far, we found that the amount of pre-existing resistance is likely to be an increasing problem with serious consequences for chosen first line therapies, though it’s true clinical value will only be amenable after correlation to clinical outcome.