The number of people in Europe who have become infected with
a drug-resistant strain of HIV may have increased by around 35% since 2003, even though
the total prevalence of drug resistance has remained stable, according to an
estimate presented at the 14th European AIDS Conference in Brussels
Previous estimates of transmitted drug resistance have
tended to focus on the proportion of the population who have acquired a
drug-resistant virus. They have placed less emphasis on the total number of
people with HIV who have acquired drug-resistant virus, despite the fact that
the number of people diagnosed with HIV infection continues to rise in all
The presence of transmitted drug resistance can cause a
number of complications for antiretroviral treatment. Although the European AIDS
Clinical Society and many national guidelines recommend drug-resistance testing
prior to starting therapy, resistance testing does not happen in all settings.
People who receive antiretroviral therapy without baseline
drug-resistance testing may fail to suppress HIV and develop further drug resistance
to agents in the first-line regimen. In settings where drug choices are
limited, transmitted drug resistance will compromise the choice of first- and
Drug-resistant virus can also be transmitted to others,
particularly where individuals have very high viral load.
Even if the proportion of people with drug resistance remains stable, an increase in the total number of people with drug resistance will imply a higher number of people requiring specialist management and diagnostics.
Marije Hofstra of Centre de Recherche Public de la Santé,
Luxembourg, presented data on behalf of the SPREAD study, analysing transmitted
drug resistance in 26 European countries. Rates of transmitted resistance were
calculated by assessing transmitted resistance by HIV exposure category for
each country, and then producing an average weighted by HIV prevalence in each
The study compared three periods: 2002 to 2005, 2006 to 2007 and
2008 to 2010. It included 8711 people, 81% male, 56% men who have sex with
The study found a prevalence of 9% across all three periods.
Prevalence among men who have sex with men was consistently higher than among
heterosexual men and women.
Taking into account the growth in HIV prevalence in all
Europe countries, the research group estimated that the number of people
infected with drug-resistant virus had increased by approximately 35% between
the periods 2003 to 2005 and 2008 to 2010, despite improvements in rates of viral
suppression in many European countries.
There was little change over time in the prevalence of
specific drug resistance mutations associated with the three major classes of
antiretroviral drugs, despite changes in the patterns of antiretroviral
prescribing in many European countries.
Dr Anna Maria Geretti of the University of Liverpool
commented that further research is needed to explain why the prevalence of
specific drug resistance mutations to the nucleoside analogue drug class
associated with AZT (zidovudine, Retrovir) and d4T (stavudine, Zerit) remained stable during the study period, despite
the decline in use of both thymidine analogue NRTIs (AZT and d4T).
A second study, of drug resistance testing in Europe, found
that only 29% of people who had experienced virologic failure (viral load
above 500 copies/ml after at least four months on treatment) had received a drug
resistance test in the following year. The study, of 8611 people enrolled in
the EUROSIDA cohort of European HIV clinics, compared the frequency of
resistance testing and the prevalence of drug resistance between five regions
Anna Schultze of University College, London, reported that people receiving care in northern Europe and western Europe were significantly more likely
to receive a resistance test, but less likely to have detectable drug
In contrast, results from eastern Europe (non-EU countries)
showed a trend towards less resistance testing, but significantly higher odds
of detecting resistance in those patients tested.
Overall, detectable resistance declined, from 85% of all
samples tested in 2003, to 74% of all samples tested in 2012.