July 12, 2016
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ART prevents HIV transmission within serodiscordant couples

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Researchers found no cases of partner-to-partner HIV transmission among nearly 900 serodiscordant couples who continued to report condomless sex while the HIV-positive partner was taking suppressive ART.

The prospective, observational PARTNER study was conducted among both heterosexual couples and men who have sex with men in Europe and included a median follow-up of 1.3 years.

“Although these results cannot directly provide an answer to the question of whether it is safe for [serodiscordant] couples to practice condomless sex, this study provides informative data (especially for heterosexuals) for couples to base their personal acceptability of risk on,” Alison J. Rodger, MD, of the research department of infection and population health at University College London, and colleagues wrote in JAMA

Thousands of condomless sex acts

During the study, Rodger and colleagues evaluated serodiscordant couples (n = 888) from 75 clinical sites in 14 European countries who reported having sex without a condom while the infected partner on ART had an HIV-1 RNA viral load of less than 200 copies/mL.

From September 2010 to May 2014, the couples (61.7% heterosexuals) reported 1,238 couple-years of follow-up. In that time, the couples reported having sex without a condom a median of 37 times per year. The total number of condomless sex acts reported by MSM couples was around 22,000. For heterosexual couples, it was about 36,000. Among MSM couples, 108 HIV-negative partners reported having sex without a condom outside the relationship, while 21 HIV-negative partners in heterosexual couples did the same.

Eleven of the HIV-negative partners in the study became HIV-positive — including 10 from MSM couples. Rodger and colleagues, however, determined through anonymized phylogenetic analysis that none of the transmissions occurred within the couples, “giving a rate of within-couple HIV transmission of zero,” they wrote. 

Authors address limitations in earlier study

In a related editorial, Eric S. Daar, MD, and Katya Corado, MD, of the Los Angeles Biomedical Research Institute, addressed several limitations of the PARTNER study, but also highlighted several ways in which it improved on an earlier study.

Daar and Corado said the PARTNER trial had limited power, underscored by raised upper 95% confidence limits for within-couple transmission per 100 couple-years. (The numbers were 0.97 in heterosexual couples where the male was HIV-positive; 0.88 in heterosexual couples where the female was HIV-positive; 0.84 for all MSM couples; and 2.7 for patients engaging in receptive anal sex with ejaculation inside the uninfected partner.)

“Even though there were no transmission events, the upper confidence limit reflects the small sample size, so that the estimated risk of transmission via this route is relatively imprecise,” they wrote in JAMA.

According to Daar and Corado, several limitations of the earlier HPTN 052 study were addressed by including MSM couples and enrolling partners who were primarily engaging in condomless sex.

“However,” they wrote, “the biology of HIV transmission and human behavior is complicated, and it is inevitable that enrollment into a study, even a cohort study, has a potential influence on these factors.”

Still, Daar and Corado concluded, the PARTNER study provides some guidance for certain couples.

“For individuals who want to routinely or intermittently not use condoms with an HIV-infected partner, clinicians can indicate that the risk of HIV transmission appears small in the setting of continued viral suppression, emphasizing that the duration the HIV-infected partner needs to be virologically suppressed before achieving optimal protection is unknown, although appears to be for at least 6 months, based on the best available data,” they wrote.

“Moreover,” they continued, “clinicians need to be clear that even though the overall risk for HIV transmission may be small, the risk is not zero and the actual number is not known, especially for higher-risk groups such as MSM.

“Although more research is needed with larger numbers of couples and longer follow-up, it is not known if or when such data will emerge.” – by Gerard Gallagher

Disclosures: Corado reports receiving research grant support from ViiV Healthcare. Daar reports receiving research grants from Gilead Sciences, Merck and ViiV Healthcare, and consulting support from Bristol-Myers Squibb, Gilead Sciences, Merck, Teva and ViiV Healthcare. Rodger reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.