Drug-resistant variants are frequently present in both recently and chronically infected therapy-naive patients. Drug-resistant variants are most commonly seen in patients infected with subtype B virus, probably because of longer exposure of these viruses to drugs. However, an increase in baseline resistance in non-B viruses is observed. These data argue for testing all drug-naive patients and are of relevance when guidelines for management of postexposure prophylaxis and first-line therapy are updated.

The role of mutations in protease (PR) and reverse-transcriptase (RT) of human immunodeficiency virus (HIV) in predicting virologic failure was assessed in 248 antiretroviral-naive HIV-positive patients who began a PR inhibitor-containing antiretroviral regimen. Genotypic testing was performed on plasma samples stored before the start of therapy. Twenty-seven patients (10.9%) had mutations in the RT, 5 (2%) carried primary mutations in the PR, and 131 (52.8%) showed only secondary PR mutations. Virologic failure at week 24 occurred in 62 (25.0%) of 248 patients. There was a statistically significant correlation between virologic failure and the number of PR mutations (P= .04, chi(2) test). Mutations at codons 10 and 36 of PR (present in 39.3% and 40.0% of patients in whom treatment failed, respectively) were identified by stepwise logistic regression as the strongest predictors of virologic failure (odds ratio, 2.20; 95% confidence interval, 1.30-3.75; P= .004). If confirmed in independent studies, this result may justify the increased use of HIV genotyping in drug-naive patients requiring antiretroviral therapy.

Background: The prevalence and the origin of HIV-1 subtype B, the most prevalent circulating clade among the long-term residents in Europe, have been studied extensively. However the spatial diffusion of the epidemic from the perspective of the virus has not previously been traced.

delta 32/delta 32 homozygosity for the CCR-5 gene does not confer absolute protection against HIV-1 infection, suggesting that either macrophage-tropic viral strains could use coreceptors other than CCR-5 or infect independently of the presence of a functional CCR-5 coreceptor. Alternatively, primary infection sustained by T-cell-tropic isolates, although exceptional, may occur.

HIV-1 215 revertants with an increased ability for selecting 215Y mutation are associated with a higher risk of virological failure and may lead to the appearance of virus carrying 215Y/F mutation in vivo. These findings suggest that 215 revertant viruses may compromise the efficacy of the first thymidine analog-containing regimen.

Based on the calculated genetic barrier, the rate of drug resistance development may be similar for different HIV-1 subtypes. Because of differences in minor protease substitutions, protease inhibitor resistance could be enhanced in particular subtypes once the relevant major substitutions are selected.

BackgroundHIV-1 non-B subtypes have recently entered Western Europe following immigration from other regions. The distribution of non-B clades and their association with demographic factors, over the entire course of the HIV-1 epidemic, have not been fully investigated in Italy. MethodsWe carried out a phylogenetic analysis of HIV-1 pol sequences derived from 3670 patients followed at 50 Italian clinical centres over nearly three decades. ResultsOverall, 417 patients (11.4%) carried non-B subtypes. The prevalence of non-B strains increased from 2.6% in 1980 -1992 to 18.9% in 1993) in a subset of 2479 subjects with a known year of diagnosis. A multivariate analysis on a subset of 1364 patients for whom relevant demographic data were available indicated that African ethnicity, heterosexual route of infection and year of diagnosis were independently associated with non-B HIV-1 infection (P 0.0001). All pure subtypes, except for clade K, and seven circulating recombinant forms were detected, accounting for 56.6 and 34.1% of the non-B infections, respectively. The F1 subtype was the most prevalent non-B clade among Europeans and was acquired heterosexually in half of this patient population. Unique recombinant forms accounted for 9.4% of the non-B sequences and showed a B/F1 recombination pattern in one-third of cases. ConclusionsThe circulation of non-B clades has significantly increased in Italy in association with demographic changes. Spread of the F1 subtype and B/F recombinants appears to predominate, which may result in a redistribution of the relative proportions of the different strains, and this could lead to overlapping epidemics. Thus, the HIV-1 landscape in Italy may in future be distinct from that of the rest of Europe. IntroductionNine discrete lineages of group M HIV-1 (A-D, F-H, J and K) have differentiated during the global pandemic as a result of massive virus replication, the very high error rate of reverse transcriptase (RT) and the selective pressure exerted by the immune system. The highly recombinogenic activity of HIV-1 RT has added further complexity to the global diversity of HIV-1 as 43 circulating recombinant forms (CRFs) have already been characterized and a number of unique recombinant forms (URFs) have been identified world-wide [1][2][3]. Most subtypes and CRFs were originally restricted to specific geographical regions or populations, but their distribution is constantly evolving [4]. In order to monitor the evolution of the global pandemic, it is convenient and effective to assign viral clades, which allow evaluation of the local epidemiological trends that result from social changes and migration flows. [6][7][8][9][10][11][12][13]. The recent epidemiology of HIV-1 infection in Western European countries with large immigrant communities has been characterized by increasing genetic diversity and a marked rise in non-B subtype strains among newly diagnosed individuals [14][15][16][17]. It has been assumed that most non-B subtype infections in Western Europe are linked to migration ...

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