Outbreak of virulent recombinant HIV strain reported among gay men in Paris region

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Public health officials in France have reported an outbreak of a recombinant strain of HIV characterised by a high viral load during early infection and rapid loss of CD4 cells.  The outbreak involved X4 tropic virus, usually associated with more advanced HIV, and is reported in Eurosurveillance by a team led by Dr Marc Wirden of the Pitié Salpêtrière Hospital in Paris.

The outbreak was focused on the Ile-de-France – the area around Paris.  A total of 49 infections had been detected by the end of 2017 and 45 of these were in gay men. The authors are certain that the actual number of cases is much higher. Using phylogenetic analysis, they were able reconstruct a transmission network, showing that the virus in each of the 49 infections shared genetic characteristics. The use of smartphone hookup apps was widely reported, and the authors suggest that they could also be used to disseminate targeted HIV prevention and testing messages.

“We show here that, even in settings in which HIV prevention and treatments are widely available, important HIV transmission chains can still emerge,” comment the authors. “These transmission chains may lead to the selection of new recombinant strains with a potentially greater capacity to spread, and new tools are required to detect them early and to optimize prevention of their spread.”


transmission cluster

By comparing the genetic sequence of the virus in different individuals, scientists can identify viruses that are closely related. A transmission cluster is a group of people who have similar strains of the virus, which suggests (but does not prove) HIV transmission between those individuals.


In HIV, different strains which can be grouped according to their genes. HIV-1 is classified into three ‘groups,’ M, N, and O. Most HIV-1 is in group M which is further divided into subtypes, A, B, C and D etc. Subtype B is most common in Europe and North America, whilst A, C and D are most important worldwide.


A variant characterised by a specific genotype.



An organism, cell or genetic material formed by genetic recombination (or reconstruction).

primary infection

In HIV, usually defined as the first six months of infection.

Between 2015 and 2017, routine resistance testing at the laboratory of the Pitié Salpêtrière identified ten HIV infections involving a new circulating recombinant form of HIV. This was suggestive of an ongoing transmission cluster involving a form of HIV combining subtype B (the dominant HIV subtype in Western Europe), subtypes A and G (both common in sub-Saharan Africa) and the very rare subtype F2.

The investigators alerted laboratories across France and asked them to report similar cases. Information on the clinical characteristics of people living with this strain of HIV was collected. Where possible, epidemiological and behavioural information was also obtained.

A total of 49 infections were identified, with all the diagnoses made between 2013 and 2017. All were white and of French origin, 48 were men and the median age was 35 years. The HIV risk group was gay men/men who have sex with men for 45 of the individuals, three were heterosexual and the likely mode of transmission was unknown for the remaining person. The most common reasons for HIV testing were symptoms of primary HIV infection (n=19) and regular testing (n=12).

Most of the individuals had been recently infected with HIV. There were 19 cases of primary infection as well as ten individuals who had been infected for less than a year. Twenty-four individuals with recent infection supplied information about their HIV risk behaviour. All were gay men and reported risky sex around the time of their likely infection with HIV. Twenty men reported finding casual partners using smartphone apps, with seven saying they used cruising areas. None were taking PrEP and 18 had not heard of it at the time of their diagnosis.

The median viral load was high, approximately 200,000 among individuals with non-primary infection and 600,000 among those with primary infection. Median CD4 cell counts were 371 and 407, in those with non-primary and primary infections respectively.

HIV tropism was identified in 26 individuals, shifting from R5 in 2013 to X4 by 2016/17. The latter tropism is usually associated with more advanced HIV disease and rapid loss of CD4 cells.

Most individuals who started antiretroviral therapy responded to treatment. Twelve-month follow-up data were available for 31 individuals, with 25 having a viral load below 50 at this time. Five people had a viral load between 50 and 100 and the remaining individual had a viral load of 5500. Average CD4 cell count was 777, a robust increase from baseline.

Phylogenetic analysis showed that all 49 cases belonged to the same transmission cluster. Four smaller sub-clusters were also identified, each with a different geographic distribution. The authors found that 14 of the 31 individuals in cluster D had either worked for or had engaged in risky sex with employees of a single company in the eastern suburbs (Seine-et-Marne). The majority (n=41) of diagnoses were made in the Ile-de-France. Four of the remaining individuals had connections with the region, three living there temporarily for work.

"Smartphone hookup apps could be used to disseminate targeted HIV prevention and testing messages."

Wirden and colleagues suggest that the use of smartphone apps may have hastened the spread of this strain. But they suggest that such apps can also be valuable health promotion tools, disseminating targeted prevention messages, with geopositioning ensuring that such information could reach individuals in outbreak areas.

“Routinely generated HIV sequence data and epidemiological information for newly diagnosed patients can be used to focus preventative activities to limit the spread of HIV,” conclude the authors. “For optimal efficiency, data collection and analysis must be more systematic, with modern tools and connected epidemiological and interventional frameworks.”