U=U: What HIV Providers Should Know

Getty/Lars Nikki

After years of programs focusing on prevention for positives, we've learned that treatment is in fact the best prevention option for people who are HIV positive. In fact, treatment works so well that people who successfully achieve viral suppression are not at risk of passing the virus on to their partners, even without using condoms or other barrier methods.

While over the last decade the science was quickly mounting evidence that this was true, it took a push from people living with HIV to begin making public health and medicine shift clinical guidelines, policies, and program priorities to address this reality. Due to community pressure and activism, the language that physicians, scientists, and public health bodies use to describe the potential for HIV transmission when a person has an undetectable viral load is now much clearer.

The slogan "Undetectable = Untransmittable" (U=U) is simple and easy to grasp. Moreover, as Anthony S. Fauci, M.D., the director of the National Institute of Allergy and Infectious Diseases (NIAID), has said, "The science really does verify and validate U=U."

U=U expresses the fact that people living with HIV who take antiretroviral medications daily as prescribed and who maintain a durable undetectable viral load do not transmit HIV to their sexual partners. When a person has had an undetectable viral load for at least six months and maintains good adherence, there is effectively no risk that he or she will sexually transmit the virus.

Talking About U=U

Language matters. When speaking with people living with HIV, their sexual partners, and the wider community, it is important to describe these facts in a way that inspires confidence and does not promote unnecessary doubts or fear.

For example, it is scientifically accurate to say that the risk of transmission in these circumstances is "negligible." However, this can sometimes be misinterpreted to suggest that a risk still needs to be taken into account or remains of practical significance.

It is preferable to use terminology that is less likely to be misunderstood. For example the Centers for Disease Control and Prevention (CDC) uses the phrase "effectively no risk" and states that effective antiretroviral therapy "prevents sexual HIV transmission." Others say that those with a durable undetectable viral load "do not transmit," "cannot transmit," or "will not transmit" HIV.

The Science Behind U=U

Data showing the relationship between an HIV-positive person's viral load and their HIV-negative partner's risk of acquiring HIV have been available for almost two decades. A key study, from a Ugandan cohort, was published in the New England Journal of Medicine in 2000.

However, the key evidence supporting U=U comes from three international research studies published since 2011. Each one recruited couples in which one partner was living with HIV and the other was not. Between them, HPTN 052, PARTNER, and Opposites Attract recruited over 3,000 couples. During the latter two studies, couples reported engaging in more than 74,000 episodes of condomless vaginal or anal intercourse.

Between these three studies, not a single HIV transmission was observed from an HIV-positive partner who had a durable undetectable viral load to an HIV-negative partner.

Although it had been hypothesized that transmission would be more likely during anal sex than vaginal sex, or if one of the partners had a sexually transmitted infection, in fact, the number of linked HIV transmissions was zero in each of these circumstances.

Some HIV transmissions did, however, occur in the first few months of a person taking antiretroviral therapy in the HPTN 052 study, before his or her viral load was durably suppressed. Individuals can, therefore, be advised to use other prevention methods if their viral load has not been undetectable for at least six months. A number of HIV-negative study participants also acquired HIV from outside their main relationships, with viral strains that were different from those of their primary partners. People who are in a relationship with a person living with undetectable HIV may need counseling on prevention with other sexual partners.

Have a look at "Key U=U Studies," below, to find out more about these studies.

It is notable that since the data from HPTN 052, PARTNER, and Opposites Attract have been released, there have been no case reports of HIV transmission from a person with HIV who had an undetectable viral load. Given the high level of public and scientific interest in this topic, it might be expected than any suspected cases would be investigated and published.

Summing up, there isn't any evidence that sexual HIV transmission occurs when a person's viral load is durably undetectable.

Factsheets and Overviews

HIV Undetectable = Untransmittable (U=U): Information for Providers (February 12, 2018)
From the New York City Department of Health and Mental Hygiene
Provides key facts about U=U and suggestions for counseling patients.

The Evidence for U=U: Why Negligible Risk Is Zero Risk (August 10, 2017)
In HIV Treatment Bulletin_, from HIV i-Base_
While the dramatic impact of antiretroviral treatment (ART) on reducing HIV transmission has been known for a long time, it is new to say that ART stops transmission completely. This article provides a thorough review of key studies from the past 20 years.

News & Opinion

Pregnancy and Infant Feeding: Can We Say U=U About the Risk of Passing HIV to an Infant? (February 14, 2018)
In Prevention in Focus: Spotlight on Programming and Research_, from Canadian AIDS Treatment Information Exchange_
Can an undetectable viral load eliminate the risk of passing HIV to an infant? This article examines what we know about the risk of passing HIV through pregnancy, childbirth, and infant feeding.

What Should We Do About Persistent Low-Level Viremia? (October 10, 2017)
From Journal Watch
Paul E. Sax, M.D., answers a question about a patient with a persistently low viral load, of around 70-100 copies/mL. Does "undetectable = uninfectious" still count?

CDC Corrects Misleading HIV Conception Guidance, Responding to Community Pressure (August 17, 2017)
From TheBodyPRO
The CDC is finally up-to-date with its HIV-affected conception guidance. It now quotes data from HIV trials showing that treatment alone can prevent HIV transmission when couples with mixed HIV status desire to have a baby.

Swaziland Dramatically Reduces HIV Incidence Through Test-and-Treat Programs (August 1, 2017)
From TheBodyPRO
The Kingdom of Swaziland has dramatically reduced the number of new HIV infections thanks to a massively expanded testing-and-treatment program, as reported at the 9th International AIDS Society Conference on HIV Science (IAS 2017).

Viral Loads Becoming Undetectable in More People Across the United States (May 4, 2017)
From the Center for AIDS Information & Advocacy
Among HIV-positive people in care in the U.S., the proportion reaching an undetectable viral load rose steadily from 2009 through 2013. Women, blacks, Latinx, and younger people were less likely to have an undetectable viral load.

HIV Researchers Reassert Treatment Is Prevention (March 8, 2017)
From TheBodyPRO
In an interview at the 24th Conference on Retroviruses and Opportunistic Infections, (CROI 2017), Fred Schaich spoke with Deborah Donnell and Matthew Golden about how getting people onto HIV treatment also prevents the spread of the virus.

HIV Undetectable Does Equal Uninfectious: The Swiss Statement and the Vindication of Pietro Vernazza (October 7, 2016)
From TheBody
In 2008, the "Swiss Statement" clearly stated that people with an undetectable viral load cannot pass on HIV. This is the story of how the Swiss Statement went from policy pariah to documented fact.

The Undetectable Problem: Dating, Sex, and Criminalization (Part 2) (September 30, 2016)
From TheBodyPRO
Expressing the author's concern that with increased focus on getting everyone seropositive to undetectable, we are creating a larger divide between people with access to care and bodily stability and those without.

Treatment as Prevention Could Nearly Eliminate HIV in MSM, Danish Study Predicts (September 16, 2016)
From TheBodyPRO
Antiretroviral treatment as prevention in Denmark could nearly eliminate the HIV epidemic among men who have sex with men, according to predictions of a Bayesian back-calculation model.

HIV Transmission Risk Remains During First 6 Months of Treatment (March 12, 2015)
From TheBodyPRO
A study from Uganda shows that in the first six months of antiretroviral therapy, a residual risk of sexual transmission exists of about 2% per year.

Minimal Risk of Sexual HIV Transmission for Heterosexual Couples When the HIV-Positive Partner Has an Undetectable Viral Load (January/February 2013)
In HIV Treatment Bulletin_, from HIV i-Base_
A systematic review of publications reporting on rates of HIV transmission between heterosexual couples where the HIV-positive partner has an undetectable viral load on ART revealed minimum risk of transmission.

Key U=U Studies

No HIV Transmissions in Couples With Positive Partner Undetectable on Treatment (November 23, 2016)
From TheBodyPRO
Results from the PARTNER study, as reported in JAMA.

Negligible Risk: Updated Results From Two Studies Continue to Show That Antiretroviral Treatment and an Undetectable Viral Load Is a Highly Effective HIV Prevention Strategy (September 6, 2016)
In CATIE News_, from Canadian AIDS Treatment Information Exchange_
Final results from HPTN 052, as reported in the New England Journal of Medicine, and results from the PARTNER study, as reported in JAMA.

Early HIV Treatment Lowers Transmission Risk by Up to 93%: HPTN 052 Final Results (August 10, 2016)
From TheBodyPRO
Final results from HPTN 052, as reported at the 21st International AIDS Conference (AIDS 2016).

Zero: No Linked HIV Transmissions in PARTNER Study After Couples Had Sex 58,000 Times Without Condoms (July 12, 2016)
From HIV i-Base
Results from the PARTNER study, as reported in JAMA.

HPTN 052: No HIV Transmissions on Effective Antiretroviral Therapy but Only Limited Data on Viral Failure and Drug Resistance (August 1, 2015)
In HIV Treatment Bulletin_, from HIV i-Base_
Results from HPTN 052, as reported at IAS 2015.

HPTN 052: No Partner Infections With Viral Suppression (July 21, 2015)
Results from HPTN 052, as reported at IAS 2015.

No HIV Transmissions Between Gay Couples When Viral Load Is Undetectable: Preliminary Results (March 24, 2015)
In HIV Treatment Bulletin_, from HIV i-Base_
Interim results from Opposites Attract, as reported at CROI 2015.

Real-World Antiretroviral Therapy as Prevention: A Top HIV Clinical Development of 2014 (December 15, 2014)
From TheBodyPRO
Results from the PARTNER study, as reported at CROI 2014.

Insight Into HIV Transmission Risk When the Viral Load Is Undetectable and No Condom Is Used (April 10, 2014)
In CATIE News_, from Canadian AIDS Treatment Information Exchange_
Results from the PARTNER study, as reported at CROI 2014.

Zero HIV Infections Seen Through Condomless Sex When HIV-Positive Partner Is on Effective Treatment (March 4, 2014)
From TheBodyPRO
Results from the PARTNER study, as reported at CROI 2014.

Early Treatment Reduces HIV Transmission in Heterosexual Serodiscordant Couples (Fall 2011)
In Prevention in Focus: Spotlight on Programming and Research_, from Canadian AIDS Treatment Information Exchange_
Results from HPTN 052, as reported at IAS 2011.

Treatment Is Prevention: ARV Treatment in HPTN-052 Reduces Transmission by at Least 96%: Single Transmission in Treatment Arm Occurred Prior to Viral Suppression (July/August 2011)
In HIV Treatment Bulletin_, from HIV i-Base_
Results from HPTN 052, as reported at IAS 2011.