Background: There is concern that transmission of multi-drug-resistant HIV could become a major public health problem. If so, it might be expected to be seen first in gay men, due to the extensive history of ART use in this group. Even though the prevalence of multi-drug-resistant HIV in newly infected people tends to be much lower than the prevalence in the pool of infectious men (for various possible reasons), future trends in the prevalence of multi-drug-resistant HIV in newly infected men are likely to largely depend on trends in prevalence of resistance in the infectious pool.

Methods:  A stochastic model (HIV Synthesis) was developed to reconstruct and project the U.K. population of infected gay men. The model reconstructs changes every 3 months in parameters including viral load, use of specific ART (including drugs projected to be available by 2010), adherence, and presence of resistance mutations, for each individual with HIV to live in the United Kingdom at any time until 2010 (160,000 30-year patient histories simulated in each run). The infectious pool at any given time point was defined as the population with viral load >1000 copies/mL, regardless of whether HIV is diagnosed. The model fits relatively closely to a wide range of observed surveillance and clinical data.

Results:  The reconstructions suggest that, despite estimates of the number of new infections in recent years, which are probably on the low side, the proportion of the infectious pool who are on ART has decreased. This is due to the well-documented increasing success of ART in suppressing viral load. The proportion of the infectious pool carrying multi-drug-resistant HIV as their majority virus, which the reconstructions suggest had grown after the initial use of the non-nucleoside reverse transcription inhibitor (NNRTI) and protease inhibitor (PI) classes to around 13% in 2002, shows a decline after that time through 2010. Similar results were found in various sensitivity analyses; e.g., transmitted mutations assumed not to persist in majority virus, different means of defining infectious, different rates of resistance appearance, and earlier initiation of ART.

Conclusions:  The projections indicate that the prevalence of multi-drug-resistant HIV as the majority virus in the infectious pool in gay men in the United Kingdom is unlikely to increase and may well decrease over the next 5 years. Similar trends are likely to be seen in gay epidemics elsewhere in resource-rich countries because our findings were similar when ART was assumed to be initiated at higher CD4 counts.