Undetectable = Untransmittable: Effective HIV Treatment Prevents HIV Transmission

In September 2017, the U.S. Centers for Disease Control and Prevention (CDC) officially recognized that suppressing HIV through antiretroviral therapy (ART) prevents sexual transmission of HIV. In a "Dear Colleague" letter, CDC officials said, "people who take ART daily as prescribed and achieve and maintain an undetectable viral load have effectively no risk of sexually transmitting the virus to an HIV-negative partner."

The statement recognizes the reality that Undetectable equals Untransmittable, or U=U. This enormously important CDC declaration will hopefully enable people with HIV and their HIV-seronegative partners to make well-informed decisions about their sexual health, and encourage medical providers to confidently discuss effective antiretroviral therapy (ART) as an evidence-based means of preventing HIV transmission.

An international U=U campaign, backed by more than 525 community partners from 70 countries, is disseminating information about the effectiveness of treatment as prevention.

A substantial body of scientific evidence shows that sustained suppression of HIV RNA, defined as less than 200 copies/mL, prevents HIV transmission. Most notable are three studies of serodifferent couples, those in which one partner is with HIV and the other is HIV-negative. In these studies, there were zero HIV transmissions from a partner who had HIV suppression on ART to an HIV-negative sex partner. Two of these studies included substantial numbers of men who have sex with men (MSM), and couples who did not use condoms; these couples had about 75,000 episodes of condomless (and PrEP-less) sex acts with no HIV transmissions (see references, below).


Bavinton B, Grinsztejn B, Phanuphak N, et al. HIV treatment prevents HIV transmission in male serodiscordant couples in Australia, Thailand, and Brazil. In: Program and abstracts of the 9th IAS Conference on HIV Science; July 23-26, 2017; Paris, France. Abstract TUAC0506LB.

Cohen MS, Chen YQ, McCauley M, et al. Antiretroviral Therapy for the Prevention of HIV-1 Transmission. N Engl J Med. 2016 Sep 1;375(9):830-9.

Rodger AJ, Cambiano V, Bruun T, et al. Sexual Activity Without Condoms and Risk of HIV Transmission in Serodifferent Couples When the HIV-Positive Partner Is Using Suppressive Antiretroviral Therapy. JAMA. 2016 Jul 12;316(2):171-81.

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