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Q&A on the PARTNER Study: How to Interpret the Zero Transmission Results

July 12, 2016

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The following Q&A are linked to the PARTNER study that was published in the Journal of the American Medical Association (JAMA) on 12th July 2016 with full free access. The technical report of this study in HTB is here.

What is the PARTNER study?

The PARTNER study is a large international study. It looked at the risk of HIV transmission when viral load is undetectable on HIV treatment (ART).

Who was enrolled?

The study enrolled 1166 couples where one partner was HIV positive and on ART, and the other was HIV negative. In order to join the study, couples had to already be having sex without condoms.

The study enrolled both gay and straight couples and the average age was about 40 years old.

How long had the couples been having sex without condoms?

There was an interesting range of time that couples had already not been using condoms.

On average this was roughly:

  • 1.5 years for gay couples (IQR 0.5 to 3.5)
  • 2.8 years for straight couples where the woman was HIV+ (IQR: 0.6 to 7.5)
  • 3.6 years (IQR: 0.7 to 11.4) for straight couples where the man was HIV+.

The IQR in brackets refers to the range for the middle 50% of each group.

So 25% of gay couples had been having condomless sex for less than 6 months.

Similarly, 25% of straight couples where the man was positive had been having condomless sex from more than 11 years.

How long had the positive partners been on ART?

This time was thought to be important because the longer someone is on treatment, the lower viral load is likely to be.

Also, the longer someone has had an undetectable viral load, the lower the risk of viral rebound.

Again there were differences with each group and between groups.

HIV positive partners had been on ART for approximately:

  • 4.8 years (IQR: 1.9 to 11.4) for gay men.
  • 7.5 years (IQR: 3.3 to 14.2) for straight women.
  • 10.6 years for straight men (IQR: 4.3 to 15.6).

When did the study run?

Enrolment took place between September 2010 and May 2014.

Early results were presented in February 2014 before the end of the study.

These final results were published in July 2016.

An extension of the PARTNER study called PARTNER 2 is continuing in gay men. This is to get an equivalent amount of data for gay men as for straight couples.

Where did the study take place?

This was a European study at 75 centres in 14 countries. These countries and centres are listed on the PARTNER website.

PARTNER 2 is still enrolling gay couples.

What were the main PARTNER study results?

The main results were that there were no linked HIV transmissions from the HIV positive to the negative partner. This was after about 58,000 times when couples had sex without using condoms.

To be included in the results, viral load had to be undetectable at the most recent test. Undetectable in this study was defined as being less than 200 copies/mL.

The results were not affected even with other STIs, They were not affected by likely viral load blips between viral load tests.

How does the study know about these risks?

Everyone in the study also provided detailed diaries about their sex lives.

This meant that the study could look at different types of risk.

For example, we have a good idea of how many times this included anal sex and vaginal sex with ejaculation by the positive partner. These are the highest sexual risks.

What is new about the published results?

Early results from PARTNER were presented at a conference in 2014.

The new results include more follow up -- now with approximately 58,000 times that participants in the study had sex without condoms (compared to 45,000 in the 2014 report).

The results have also now been extensively reviewed by other experts. The results have been published in one of the world's leading medical journals.

The study still reports zero linked transmissions.

What is special about the PARTNER study compared to other transmission studies?

Most other studies only reported relative risks -- for example comparing the risk from being on ART compared to not being on ART.

PARTNER was able to estimate actual risks for different types of sex

Importantly, all risks are estimates to be zero -- even for highest risks when the positive partner comes inside the negative partner.

This is after approximately 58,000 when couples had sex without condoms.

How many people became positive from their partner?

Zero. There were no transmissions within couples when viral load was undetectable.

Were there other HIV transmissions?

Yes, 11 people did become HIV positive during the study (ten gay men and one heterosexual). In nearly all these cases, the person said that they had sex with another person other than their main partner.

Approximately 33% of gay couples and 4% of straight couples were in open relationships.

Importantly, none of these transmissions were linked to their HIV positive partner.

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This article was provided by HIV i-Base. Visit HIV i-Base's website to find out more about their activities, publications and services.

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