Declining prevalence of HIV-infected individuals at risk of transmitting drug-resistant HIV in Denmark during 1997-2004

BACKGROUND: Transmission of drug-resistant HIV is a potential threat to the substantial clinical benefit of highly active antiretroviral therapy (HAART). To explore the background for the low rates of drug resistance transmission (2.5%) in our population, we estimated acquisition of HIV drug resistance and examined temporal trends in the prevalence of patients at risk of transmitting drug-resistant HIV. METHODS: The study population included all 4,025 patients from The Danish HIV Cohort Study seen during the period 1995-2004. Virological failure to a given drug class was defined as a viral load (VL) > 1,000 copies/ml for 120 days while on a HAART regimen including that drug class. In addition, receiving nucleoside reverse transcriptase inhibitors (NRTIs) for 180 days before HAART counted as NRTI failure irrespective of VL. Having experienced failure was considered a proxy for harbouring drug-resistant virus in subsequent observation time. Patients with a current VL > 1,000 copies/ml were considered at risk of transmitting HIV. RESULTS: We found a decrease from 1997 to 2004 in the prevalence of potential transmitters of drug-resistant HIV. The number of these patients with previous NRTI failure decreased from 429 (24% of all patients) in 1998 to 213 (8.0% of all patients) in 2004. Previous protease inhibitor (PI) failure peaked at 279 (14%) in 1999, declining to 142 (5.3%) in 2004. Previous NNRTI failure peaked at 121 patients (4.7%) in 2002, and occurred in 113 patients (4.2%) in 2004. Of all 686 potential transmitters in 2004, 31% had previously experienced NRTI failure, 21% PI failure, and 16% non-NRTI failure. CONCLUSION: In the population of HIV-infected individuals in Denmark with complete follow-up, the number at risk of transmitting drug-resistant virus declined over time.