Risk of high-level viraemia in HIV-infected patients on successful antiretroviral treatment for more than 6 months.

OBJECTIVES: According to the Swiss Federal Commission for HIV/AIDS, HIV-infected patients on successful antiretroviral treatment have a negligible risk of transmitting HIV sexually. We estimated the risk that patients considered to have an undetectable viral load (VL) are actually viraemic.
METHODS: A Danish, population-based nationwide cohort study of HIV-infected patients with VL <51 HIV-1 RNA copies/mL for more than 6 months was carried out for the study period 2000-2008. The observation time was calculated from 6 months after the first VL <51 copies/mL to the last measurement of VL or the first VL >50 copies/mL. The time at risk of transmitting HIV sexually was calculated as 50% of the time from the last VL <51 copies/mL to the subsequent VL if it was >1000 copies/mL. The outcome was the time at risk of transmitting HIV sexually divided by the observation time.
RESULTS: We identified 2680 study subjects contributing 9347.7 years of observation time and 56.4 years of risk of transmitting HIV (VL>1000 copies/mL). In 0.6% [95% confidence interval (CI) 0.5-0.8%] of the overall observation time the patients had VL >1000 copies/mL. In the first 6 months this risk was substantially higher (7.9%; 95% CI 4.5-11.0%), but thereafter decreased and was almost negligible after 5 years (0.03%; 95% CI 0.0-0.2%). The risk was higher in injecting drug users, but otherwise did not differ between subgroups of patients.
CONCLUSION: The risk of viraemia and therefore the risk of transmitting HIV sexually are high in the first 12 months of successful antiretroviral treatment, but thereafter are low.