Newly infected individuals sustaining HIV epidemic in Geneva

Michael Carter
Published: 14 August 2012

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 treatment.

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 blunted.


Ambrosioni J et al. Impact of HAART on the molecular epidemiology of newly diagnosed HIV infections in Geneva, Switzerland. AIDS 26, online edition. DOI: 10.1097/QAD.0b013e32835805b6, 2012.   

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