evidence about the impact of treatment on the risk of HIV transmission largely
comes from big randomised controlled studies. For instance, a study in Africa
last year found that the chances of HIV being passed on between partners was
reduced by 92% - better than the average reduction due to attempted consistent
condom use – if the HIV-positive partner was on treatment.3 That’s a big treatment bonus.
enrolled in these trials generally receive a lot of support and good medical
care. Often this is at a higher level than is available from routine medical
‘real-world’ evidence from the US
has suggested that high rates of treatment within the community may be starting
to help prevent new infections.
researchers also looked at this question recently, and found a result that was
completely out of line with this.4
Their research involved 1927 couples where one partner was HIV-positive and the
other HIV-negative. These couples were monitored for approximately three years.
transmission rate in couples where the HIV-positive partner was taking
treatment was 5%, compared to a transmission rate of 3% in the other couples. That
makes it look as if taking treatment was worse in terms of infectiousness than
not taking it, but in statistical terms the 2% difference is within the margin
of error, and it essentially means the risk was the same, regardless of
treatment. Nonetheless, this is a drastically different result from the African
editorial that accompanied the study, Myron Cohen, a senior US HIV doctor, said
the results of this study should cause those who support the wider use of HIV
treatment as a way of controlling the spread of the virus to “pause”.5
was the result so wildly out of line? In their own paper, the researchers note
that people on treatment who did not switch their regimens were much more
likely – nearly three times as likely – to transmit HIV than people who had
switched their drug regimens.
this be a clue? Well, the researchers did not provide any information on the
viral load of the individuals who transmitted HIV to their partners, about
whether they had drug resistance, or about measures to support adherence.
they also noted that a previous study of drug resistance in Henan province found
that only one third of people with HIV were adherent to their treatment after
six months of therapy, and that by this time (from an original figure of 14%
with drug-resistant HIV), no less than 63% had drug resistance.6
tell if the same situation applied in this study. But if adherence is poor and people
in this region do have high rates of resistance, perhaps due to a lack of
support or treatment education, then failing to switch therapies might mean
they are much more likely to have drug-resistant HIV – which they then transmit
to their partner – than they are if they move to a new therapy.
get more information, we won’t know if that’s the explanation and, as Dr Cohen says,
this gives us pause for thought. However, what this study may be showing us is
simply that suboptimal treatment regimens and levels of support produce
prevention failure as well as treatment failure.