Individuals with recent HIV infection are
sustaining the epidemic, a Swiss study published in the online edition of AIDS suggest. The investigators believe
that their results further support the use of antiretroviral therapy as
prevention, but also show that its impact on the epidemic will be blunted
because of the high number of transmissions which can be attributed to
individuals who have been recently infected with HIV and who are not yet taking
Phylogenetic analysis showed that only a
handful of infections in individual diagnosed between 2008 and 2010 could be
attributed to patients diagnosed before 2000. Patients with longer-term HIV
infection were the group most likely to be taking antiretroviral therapy and to
have an undetectable viral load.
“Recent HIV infections were a significant
source of HIV spread,” comment the authors. “By contrast, HIV individuals
diagnosed before 2000 were rarely the source of new infections before 2008.”
It is now widely accepted that patients who
are taking HIV therapy that suppresses their viral load to undetectable levels
are highly unlikely to transmit the virus to their sex partners.
However, even in countries with widespread
free access to antiretrovirals there continue to be large numbers of new infections.
A possible reason could be that many of
these transmissions originate in individuals who have only recently been
infected with HIV. Many of these patients will be unaware that they have HIV
and few will be taking anti-HIV drugs.
The molecular epidemiology of the HIV
epidemic in Geneva, Switzerland, has been studied in detail since the 1990s. A
retrospective analysis of blood samples obtained from patients diagnosed in
three periods (before 2000; 2000 to 2008; and 2008 to 2010) allowed investigators
to establish if the epidemic was indeed being sustained by individuals with
more recent infection.
Phylogenetic analyses were performed on 780
newly diagnosed individuals between 2000 and 2010 (142 between 2008 and 2010)
and 1058 patients diagnosed before 2000. This type of analysis is able to
identify clusters of HIV transmissions.
A total of 214 clusters were found, their
size ranging from two to 13 infections. Some 35 clusters included at least one
individual diagnosed between 2008 and 2010.
Overall, 42% of patients diagnosed in the period 2008 to 2010 could be
placed within a cluster.
Almost two-thirds (65%) of patients
diagnosed between 2008 and 2010 belonged to new clusters of infections, and 41%
belonged to clusters exclusively composed of patients diagnosed in this most
recent time period. Just over half of the infections belonged to transmission
network involving patients diagnosed between 2000 and 2008. Only 8% belong to
clusters where all the other members were diagnosed before 2000.
The investigators then conducted an
analysis to see what proportion of patients in each time period belonged to a
transmission cluster which involved individuals diagnosed between 2008 to 2010.
Overall, 66% of patients diagnosed between
2008 and 2010 could be placed with such a cluster. This compared to just 2% of
all patients diagnosed before 2000.The transmission dynamics revealed by the
authors appeared to be related to the likelihood of each group of patients
taking antiretroviral therapy and having an undetectable viral load.
Some 84% of individuals diagnosed before
2000 were taking anti-HIV drugs and 50% had an undetectable viral load.
Three-quarters of individuals diagnosed
between 2000 and 2008 were taking HIV therapy and 42% were undetectable. In
contrast, 51% of patients diagnosed in the most recent time period were treated
with antiretrovirals and only 7% had a viral load below the limit of detection.
Median viral load also differed between the
three groups of patients and was significantly higher for patients diagnosed
between 2008 and 2010 (p = 0.001).
“We show that the epidemic is only
marginally fed by individuals diagnosed over a decade ago,” comment the
researchers. “This may be related to their lower viral load as a consequence of
HAART coverage…by contrast, recently infected, untreated individuals are a
frequent source of new infections in Geneva.”
The investigators believe that prevention
campaigns need to be focused “on improving diagnosis for recently infected
individuals who represent an important source of HIV transmission.” They
caution that unless measures to increase testing and earlier diagnosis are not
implemented then the ability of HIV treatment to contain the epidemic will be