Semen goes viral – or does it?

Published 17, Apr, 2012
Author // Bob Leahy - Publisher

If you have an undetectable viral load, is your semen undetectable too? Researchers say it may not be. But what’s the likelihood of actual HIV transmission? And how should we process that risk? Bob Leahy reports.

Semen goes viral – or does it?

There has been a flurry of articles recently with headlines like “Undetectable Viral Load? Not Necessarily in Semen” like this one in POZ.  Discovery of this connection isn’t the least bit new, of course, but what’s drawn attention is new research from Boston which furthers our understanding of the associated risk a little more. More on what that research says in a moment.

The headlines may sound alarming for those who thought, because they’d reached undetectable, they were much less infectious because of low levels of virus in their blood. But if there is in fact virus in the semen, are we back to square one, the walking time bombs we’ve always been? Certainly the headlines seem to imply that. And certainly the headlines seem to reinforce the message for poz guys everywhere “wear a condom, whatever your viral load”.  But do the headlines reveal the full picture?

It’s clear we’ve made good progress towards quantifying what IS the risk of virus in the semen, and in the associated risk of HIV transmission. Today I want to look at what we’ve learned and what are the implications for people living with HIV.

Semen – the traditional view

The virus in the blood vs. virus in the semen debate is a complicated and technical one. As a result, there has been a tendency for prevention experts to try and make things simple for us. Here’s how CATIE, for example, answers the question “If my viral load is undetectable, can I still pass HIV to others? 

“Yes. While HIV may not be detectable in the blood, there might still be enough to infect someone. Also, there may be higher levels of HIV in semen or vaginal secretions. So, even if you have an undetectable viral load, you might still infect someone if you share needles or have unprotected sex.”

There is nothing here that isn’t absolutely correct.  But the answer doesn’t help quantify the risk for us – and quantifying risk, or trying to, is exactly what informed decisions are built on. In this particular case, we need to know what science tells us about three key questions:

  • What is the likelihood of virus appearing in the semen if it can’t be detected in the blood?
  • Where virus is detected in semen, what are the likely concentrations?
  • Are those concentrations likely to cause HIV transmission?

All three questions are answerable, albeit with provisos, from research. That research suggests, in a nutshell, that while a quarter of ‘undetectable’ gay men have HIV in semen, the risk of transmission is likely quite low.

The research on “undetectable” gay men’s semen.

The Boston research has helped quantify the likelihood of both virus being present in the semen in "undetectable" men and the likelihood of it causing transmission. This study involved 101 gay/bi men. This AIDSmeds article summarizes the results. Eighty-three of the 101 men had undetectable levels of HIV in their blood samples. Though most also had undetectable HIV in their semen samples, 25% of those had detectable seminal viral loads. This is in the range that previous studies have confirmed.

What’s interesting is that the men who had an STI were 29 times more likely to have viral discordancy. The implication is that without an STI, undetectable in the blood means, way more often than not, undetectable in the semen.

Now let’s look at those 25% of undetectable men where virus was detected in their semen, because it’s important to understand how much virus was present.  The median level in the semen was 200 - in other words, unlikely to infect anyone.  A viral load below 1,000 has in fact, rarely been associated with HIV transmission.

So let’s summarize what we’ve learned from Boston: if you have an undetectable viral load there is a one-in-four chance of virus being measurable in your semen, considerably smaller if no STIs are present. And if that virus in your semen reflects median levels found in the study, the chances of transmission are tiny.

The problem is that median levels are just that – some men will in fact have higher levels of seminal virus, thus increasing the risk of transmission.  So, while the median range for measurable semen may have been 200, the actual range was 80 to 2,560 copies. We need to look at other research to find out whether those higher levels of seminal virus are likely to cause transmission.

It’s not as clear cut as one would like, but AIDSmap reports a small 2008 study from San Francisco found that the median seminal viral load in men transmitting HIV to partners was 4,300 and the lowest was 110. A larger (1,199 gay men) 2009 study from the UK found that two out of 41 transmissions of HIV (5%) were from men with an apparently undetectable viral load, as measured in their blood.

BUT as AIDSmap  qualifies “studies of the link between viral load and transmission suffer from it being difficult to pin down transmitters in a cohort of gay men with multiple partners and where viral load may be measured months after the transmission.”  In other words, it is wrong to conclude the men had undetectable virus (in the blood) at the time of transmission.

What does all this mean? It’s hard not to suggest that in “undetectable” men, virus in semen at levels likely to result in HIV transmission represents anything other than a small but nevertheless potential risk.

How we process risk.

It’s notoriously difficult to turn research data like this in to helpful risk guidelines, a topic which was explored in some depth in my recent interview with CATIE’s James Wilton here

What is clear is that the risk associated with semen in otherwise undetectable men is low, but cannot be expressed as zero.

But what risk CAN be expressed as zero? Certainly not with  condoms, the cornerstone of our HIV prevention programs.  A recent literature review reported in CATIE concluded condoms can be highly unreliable. CATIE summarizes “The review found that there is a variety of ways in which condoms are being used incorrectly and the prevalence of incorrect condom use is surprisingly high.”  That and breakages, even when condoms are used properly, present an alarming  picture.  Breakage and slippage or complete failure of the condom to afford protection was reported in 25-45% of those studied, with an event rate of up to 8%.  (“Fit or feel” issues, by the way, were reported in 7-30% of those  studied and in up to 45%  of events, with erection difficulties reported by 19-20%  and up to 20% of events.)

How do condoms stack up to undetectable viral load as a means of affording protection?  Some prominent advocates have suggested that the use of condoms in people living with HIV affords LESS protection than having an undetectable viral load.  Respected POZ magazine founder Sean Strub said that here. Even Canada’s most prominent AIDS researcher, BC’s Dr Julio Montaner said in a interview “I’m very comfortable that HAART is at least as protective – or more – than condoms.”

Overall though, we’ve been slow to acknowledge the risk from unprotected sex amongst sero-discordant partners has changed radically since the advent of undetectable viral load.  But here’s a recent exception. The ever-progressive Heath Initiative for Men (HiM) said just this month ”Most of the time, guys with undetectable blood viral loads who are taking treatment as prescribed, and get tested regularly for STIs (and treated if need be), also have undetectable viral loads in cum and rectal secretions.”

They go on, very significantly, that “for some gay men, if their partner is on treatment as prescribed by his doctor, has an undetectable blood viral load that is monitored regularly and is getting tested (and treated if need be) for STIs regularly, their risk of picking up HIV is greatly reduced, even without condoms. This may be something you want to talk about with your partner, together with his doctor.”


Given the evidence, even with its gaps, it’s not unreasonable to suggest that  the risk of transmission associated with semen when your blood viral load is undetectable has been over emphasized and overstated.  Why? It’s hard not to think it’s connected with our desire to see condom use maintained.

Not that this desire isn’t well founded. Condoms may not be 100% effective, or even close, but they are the best prevention technology we have right now.  So let’s be clear; it’s inappropriate for people living with HIV to stop using condoms, whatever their viral load, without carefully reviewing the risk to themselves and their partners.  That, as HiM suggests, may involve discussion with your partner and your doctor, hopefully an informed one.

But ultimately it depends, as does life in general, on what risk you consider reasonable. You make similar informed decisions every time you cross the road. writer Michael Bouldin saidIt’s not that we don’t know what constitutes risky behavior; it’s that it’s simply not possible to always avoid it, or in a given moment even desirable. Walking a red light can get you killed; it can also get you to a job interview on time.”

How we process risk is fluid too.  It depends on the context – the time, the place, the partner – and to what extent we are informed.  And to be frank, there are problems here. Canadian Treatment Action Council (CTAC) chair  Alex McLelland recently said on “As a community, we have not developed or even responded with relevant guidelines on how to incorporate the new reality that people living with HIV who are on treatment and have viral suppression do not always need to use condoms.”   

So risk is a very fluid concept for us consumers, isn’t it? It’s less so for HIV educators, who need to ensure that anything less than zero risk constitutes a warning shot across our bows.

Warning shots are fine and we need them. But we need to interpret them, try to qualify the degree of risk that might apply to us, just as we hover on the curb before crossing the road. In the case of the danger of virus in semen in those of us who are undetectable, the warning shot doesn’t pack a lot of punch for me, if you peel its skin away and look at the underlying research. But your experience may vary. In the context of informed decision making, you really need to make up your own mind.

About the Author

Bob Leahy - Publisher

Bob Leahy - Publisher

Award-winning blogger Bob Leahy first made his social media mark a decade ago on where there are still to this day almost 3,000 entries of his available to be read. He was a featured blogger on Ontario’s campaign, along with founder Brian Finch. He joined at its inception in 2009 and became it's Editor a year later.

Born in the UK, Bob’s background is in corporate banking, which he gladly left in 1994, after being diagnosed with HIV the previous year.  He has chaired the board of PARN (Peterborough AIDS Resource Network) and has been an executive board member of both the Ontario HIV Treatment Network (OHTN) and the Canadian AIDS Society (CAS).  He was inducted in to the Ontario AIDS Network’s Honour Roll in 2005.  Bob is currently a member of Ontario’s GMSH (Gay Men’s Sexual Health Alliance). He also writes for

In 2012, Bob was honoured with the Queen Elizabeth II Diamond Jubilee medal for his work and commitment to HIV/AIDS in Canada.

Bob continues to write for this site while in the Positivelite.Com editor’s seat, with a particular interest  in HIV prevention, theatre and the arts in general. He is accredited media for a number of Toronto theatres. He lives in Warkworth, Ontario with his partner of thirty-two years and three dogs.