It is unclear whether unfit virus with little capacity to replicate will mean slower progression. Three studies in recently infected individuals found no evidence of a slower rate of disease progression in terms of CD4 cell loss^[1][2][3].

However, San Francisco researchers have produced contradictory conclusions, finding that those with genotypic evidence of drug resistance or virus with reduced replication capacity had significantly higher CD4 cell counts after controlling for duration of infection ^[4].

At the Seventh International Congress on Drug Therapy in HIV Infection in 2004, Dr Mark Wainberg of McGill University AIDS Centre in Montreal, Canada, argued that the clinical consequences of infection with multidrug-resistant virus were unpredictable, varying from repeated treatment failure to long-term non-progression. Low replicative capacity of multidrug-resistant virus may correlate with low viral load and delayed progress, but this theory is yet to be proven.

Of course, acquiring drug-resistant HIV is assumed to reduce treatment options. Resistance testing can be used to select active regimens for many people in this situation, and there is evidence that baseline resistance may not affect the short-term efficacy of first-line treatment when selected to account for resistance ^[5][6]. However, experts suspect that second- and third-line therapy may be compromised. NRTI and NNRTI resistance has been linked a greater risk of death in a large Canadian cohort followed between 1996 and 2003 ^[7].

Effects of acquiring drug-resistant virus appear to differ by class. Compared to recent seroconverters with wild-type virus, those with PI- and NRTI-associated resistance have shown consistently lower viral loads over time, and those with NNRTI-associated resistance had significantly higher viral loads over time ^[8].