The detection and control of acute (very recent) HIV
infection may be a powerful HIV prevention measure in HIV epidemics in men who
have sex with men (MSM), Eugène Kroon of the Thai Red Cross AIDS Research
Center told a late breaker session at the 7th International AIDS Society Conference on HIV
Pathogenesis, Treatment and Prevention in Kuala Lumpur this week.
An HIV testing programme in Bangkok, Thailand, was able to
identify a considerable number of men who have sex with men who had only been
infected with HIV for a few weeks, he reported. Moreover, most of
those identified accepted the offer of immediate antiretroviral therapy,
resulting in dramatic drops in viral load in blood and semen.
The HIV epidemic in young Thai men who have sex with men
continues to grow at an alarming speed. Last week one of
the key Bangkok HIV testing centres reported that, in 2011, 28.3% of new
patients were already infected with HIV. Amongst existing patients, eight in
100 newly acquire HIV each year.
As in many other situations where there are high rates of
partner change, it is likely that individuals who have themselves been very
recently infected with HIV but are unaware of the fact make a disproportionate
contribution to the number of new infections which occur.
Researchers in Bangkok have been working to identify, treat
and follow a cohort of people with acute HIV infection, primarily for basic
science purposes. They aim to describe the clinical, immunological, and
virological characteristics of acute infection, to inform the development of
vaccines. Furthermore, a better understanding of the effect of HIV treatment during
acute infection may help the development of a functional cure.
But the project also aims to describe the demographics and behavioural
risk factors of those identified with acute HIV infection.
Blood samples of people attending HIV testing clinics in
Bangkok were screened for acute HIV infection using nucleic acid testing (as is
used in screening blood donors), a p24 assay, antibody testing and Western
Blot. As each of these has a different ‘window period’ during which it cannot
detect a recent infection, the contrasting test results can suggest the likely
duration of a person’s infection.
Over four years from 2009, 69,911 samples were tested and
136 were found to be cases of recent infection. Almost all were samples from
men who have sex with men.
Kroon presented data on 90 of these MSM. Most were in their
twenties or early thirties and were thought to have been infected for between
10 and 23 days.
The laboratory facilities in place meant that their acute infection
was usually identified within three days of samples being taken. The
individuals were immediately contacted, counselled and invited to go on
antiretroviral therapy – 88 of the 90 did so.
As a result, viral load levels dropped dramatically. Whereas
the average blood plasma viral load was around 5 log10 copies/ml for
the first two weeks, 22% of the men were undetectable by week 4, rising to 55%
at week 8, 80% at week 16, 91% at week 24, and 97% at week 48.
Similarly, 59% of seminal plasma samples were undetectable
by week 2, 73% by week 4, 95% by week 12 and 100% by week 24.
Kroon noted that, in men not taking antiretroviral
treatment, seminal viral load usually peaks a month after infection, whereas
there was a sharp and rapid decline in this cohort. This will have a
substantial impact on the risk of onward transmission.
What’s more, although the researchers did not describe in detail the risk reduction counselling which was provided, it appears to have
At baseline, 55% of the men had reported having between two and four
sexual partners in the previous month, and 30% reported having more than five.
By week 24, these figures had dropped to 32 and 7% respectively.
Moreover, at baseline 84% of men reported having had unprotected
anal intercourse in the previous four months (including 57% reporting it with a
casual partner). By week 24, the figures had dropped to 25 and 8%.
Kroon said that, whereas he wasn’t particularly surprised
to see these reductions in the first few months after diagnosis, he was very
surprised that the behaviour change was maintained up to week 48 (eleven
months). For each of the behavioural indicators just reported, there were no statistically
significant differences between the figures at weeks 24 and 48.
In the Bangkok programme, there appears to be a synergy
between the effects of immediate antiretroviral therapy and the impact of behaviour change. Kroon said that the preliminary results of modelling work
conducted by David Wilson suggested that when an individual with acute
infection receives the intervention, it may avert 78% of onward transmissions in
the first six months after infection.