Undetectable equals untransmittable

Timely identification of HIV-infected individuals and early treatment is a promising strategy for tackling the HIV/AIDS epidemic. There is less available data to estimate HIV-1 transmission risk in serodifferent gay partnerships (in which the HIV-positive partner is taking antiretroviral therapy (ART)) than data on transmission risk in heterosexual couples. Now, an observational study of 782 gay couples across Europe between 2010 and 2018 reports that men whose HIV-1 infection was fully suppressed by ART had zero chance of infecting their partner. The authors monitored sexual behaviour, HIV-1 status of HIV-negative partners and the viral load of HIV-positive partners, which provided results over 1,593 couple-years of follow-up, including 76,088 cases of condomless anal intercourse. No cases of within-couple HIV-1 transmission were detected, which suggests that individuals who achieve and maintain an undetectable viral load cannot sexually transmit HIV.


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  1. Rodger, A. J. et al. Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study. Lancet https://doi.org/10.1016/S0140-6736(19)30418-0 (2019)

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Correspondence to Ashley York.

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York, A. Undetectable equals untransmittable. Nat Rev Microbiol 17, 399 (2019). https://doi.org/10.1038/s41579-019-0215-4

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