Background: Development of resistance to antiretroviral drugs remains an important cause of treatment failure in HIV-infected patients, and has been associated with increased mortality. Drug resistance can also be transmitted upon infection and causes subsequent inferior response to treatment. It is important to monitor the level of resistance in different populations as the prevalence varies in different regions. This study investigated the prevalence in a cohort of both antiretroviral treatment (=ART)-experienced and ART-naïve HIV-infected individuals in Oslo. We also investigated for potential differences in resistance within the subgroups gender and socio-cultural background.
Methods: We performed a retrospective observational study on data from the HIV-cohort database at Ullevål University Hospital. Patients having at least one genotypic resistance test in the time period between 2003 and 2008 were included. Patients were stratified into two groups, ART-naïve and ART-experienced. Resistance mutations were identified, and clinical resistance to NRTIs (divided into lamivudine and other), NNRTIs and PIs respectively was predicted by the means of an algorithm developed from the IAS-USA list of mutations. The prevalence of resistance to at least one drug class was calculated for each of the two main groups, as well as for the subgroups gender and socio-cultural background (labeled western/non-western).
Results: The study included 665 resistance tests from 547 patients, of which 399 tests were from ART-naïve and 266 from ART-experienced. We found a low overall prevalence of resistance among the ART-naïve, and a decreasing prevalence among the ART-experienced. In the latter group resistance to NRTIs was most common. In the ART-naïve resistance was detected more often in non-western females than in western males, and this was most apparent for NNRTI-resistance. In the ART-experienced there were no differences in overall prevalence between gender and sociocultural background, but some differences were observed within the individual drug classes, with proportionately more western males harboring resistance to PI and NRTIs (other than lamivudin) than non-western females.
Conclusion: Our findings regarding the overall prevalence in both ART-naïve and ART-experienced are in agreement with other studies from Europe and North America. The decreasing prevalence is most likely due to more efficient treatment in the recent years and shows that resistance can be kept at a low level in spite of increased availability of antiretroviral treatment. Further studies are needed to clarify whether the observed differences in prevalence of resistance at the subgroup level are due to local variations in access, prescription and utilization of drugs, genetic factors or other reasons.