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February 10, 2009 (Montreal, Quebec) – The belief that undetectable plasma HIV RNA means lower risk of viral transmission through seminal fluid may hold true on a population level, but not when applied at the individual level, according to new data presented here at the 16th Conference on Retroviruses and Opportunistic Infections.

Prameet Sheth, MD, from the University of Toronto, in Ontario, and colleagues conducted a longitudinal study in a cohort of 25 participants who were initiating highly active antiretroviral therapy (HAART). They were seen every 2 weeks for the first month, then monthly for 5 months. HIV RNA became undetectable in blood for all of them by week 16, but nearly half (48%) still had detectable virus in their seminal fluid.

Some of the lower levels of viremia likely did not have clinical significance, nor did they pose substantial risk of transmission. But 4 of the 25 (16%) participants surpassed 5000 copies/mL, and 1 reached 16,000 copies/mL of HIV RNA, which was cause for concern. One patient completely suppressed plasma viremia within 4 weeks of starting therapy but "was a sustained semen shedder" out to the end of the 6-month study.

Isolated Shedding Episodes

Dr. Sheth studied a second cohort of 13 men who had been receiving HAART and who had an undetectable viral load in their blood for at least 4 years and reported that 4 had isolated HIV shedding episodes in their semen.

"We did see quite a differential in the penetration of drugs; 3Tc was present in seminal plasma [at a rate] 100-fold higher than it was in blood, but we were still able to get isolated HIV shedding in these individual," said Dr. Sheth. "There was no evidence of drug resistance in the virus in the compartments."