Sixth International Congress Drug Therapy in HIV Infection 17-21 November, 2002 Glasgow, UK

Effective combination therapy can reduce HIV transmission but the benefits are reduced by the selection and transmission of drug resistant strains. We analyzed treatment rates, response to antiretroviral (ARV) therapy and transmission of ARV-resistant HIV in San Diego from 1997 onwards, using an empirical epidemiological model to obtain projections of future trends.

Drug resistant (DR) virus (10-fold or greater reduction in IC₅₀ relative to HIV-1NL4-3) was assayed with HIV PhenoSense. in patients with evidence of primary HIV infection (predominantly MSM). ARV therapy rates and suppression rates were evaluated from the UCSD HIV specialty clinic, which saw 20% of persons living with AIDS in San Diego in 2001. We used a differential equation model incorporating time-dependent recruitment rates and rates of suppression. Infection rates were estimated by back-calculation based on the observed AIDS incidence in San Diego county. Sensitivity analyses were performed by assuming upper and lower bounds for parameters under multiple model runs, selecting combinations of parameter values that gave a good fit to the incidence data.

In 2000-2002, HIV resistant to one or more ARV drugs was detected in 9% (9/101) of patients with primary HIV infection in San Diego, similar to 1999-2000 (10%) but higher than in 1996-1998 (2%, p= 0.05). Patients receiving 3 or more ARV drugs at the study clinic rose from 295 in 1997 to 1062 in 2002. The % of these subjects with virological suppression rose from 25% to 70% over the same period. The model was fitted to the observed numbers treated and suppressed to estimate future trends in transmission of drug resistant HIV. The model projects that even with over 60% of patients on ARV suppressed, the % of newly infected patients infected with drug resistant HIV will gradually increase. These individuals will form an increasing proportion of patients failing ARV therapy, and will themselves be responsible for an increasing proportion of transmissions of ARV resistance.

Despite an increasing proportion of individuals receiving ARV therapy and achieving virological suppression, transmission of drug resistant HIV is expected to continue. Increased efforts at early diagnosis and resistance testing for all recently infected individuals is warranted to ensure they receive optimal therapy.

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1 University of Edinburgh, Edinburgh, UK

2 University of California San Diego

3 Harbor-UCLA

4Virologic Inc., USA

2002-11-17
PL3-4

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