Dr Fiona Bisshop

You’ve been cruising along with an undetectable viral load for years and then suddenly one day, the horror, you go to your routine appointment and your doctor tells you there’s an actual detectable number for your virus.  Maybe 30, 50 or 100, instead of the usual <20 result.  It’s OK your doc says, it’s nothing to worry about, it’s just the new assay the lab is using.

Viral load refers to the number of copies of virus detectable in your bloodstream.  It’s measured by a sophisticated lab machine and reported as how many millions of copies per ml they could measure.  As with all technology, it has improved over time, and the lab assays have become more sensitive.

Imagine you’ve been trying to count sheep on a distant hillside using an ancient telescope, and then one day someone gives you a really fancy set of binoculars – suddenly you can see sheep you’ve never seen before.  They’re not new sheep, they have always been there, you just couldn’t see them before.  The newer assays the labs are using for detecting virus are a bit like a new set of binoculars.

So what does it actually mean to have a viral load of 30 or 50.  Well here’s what it doesn’t mean.  It doesn’t automatically mean your meds are failing or your virus is resistant.  If you are good at remembering to take your meds then resistance is extremely unlikely to develop.  If your viral levels are not going up, up, up at each follow-up test, then you do not have treatment failure.

But if the meds are working then why is there any virus detectable at all?

Remember that HIV infects immune system cells called CD4 T cells, and while many cells die after they are infected (thus lowering your CD4 count), some of these cells live a very very long time.  Eventually they do die and the virus contained within them is released, and may be detected.  However, if you’re on effective meds then this newly released virus can’t actually infect any other cells, so it can’t replicate.

Now your next question is going to be about U=U (undetectable equals untransmittable) and contagion risk, right?

The good news is that in the huge studies looking at this, the cut-off used for undetectable was 200, not 20 or 50 or even 100, so your low-level viraemia is irrelevant and does not put your sexual partner at risk.  (see results of the PARTNER 2 study here)

Persistent viral loads above 200 are another story however, and no doubt your doctor will be doing resistance tests in this situation and will advise condoms or PrEP for your partner.

The take home message is that sudden new low level virus detection if you’re usually undetectable and take your meds is definitely not a disaster and you should not freak out!