Number of people infected with drug-resistant HIV in Europe has risen by around 35%

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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 today.

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 European countries.

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.


drug resistance

A drug-resistant HIV strain is one which is less susceptible to the effects of one or more anti-HIV drugs because of an accumulation of HIV mutations in its genotype. Resistance can be the result of a poor adherence to treatment or of transmission of an already resistant virus.

resistance testing

Laboratory testing to determine if an individual’s HIV strain is resistant to anti-HIV drugs. 

detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.

second-line treatment

The second preferred therapy for a particular condition, used after first-line treatment fails or if a person cannot tolerate first-line drugs.


In everyday language, a general movement upwards or downwards (e.g. every year there are more HIV infections). When discussing statistics, a trend often describes an apparent difference between results that is not statistically significant. 

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 second-line treatment.

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 exposure category.

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 men.

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 in Europe.

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 resistance.

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.


Hofstra M et al. Increasing number of HIV-1 diagnoses with transmitted drug resistance across Europe despite stable prevalence. 14th European AIDS Conference, Brussels, abstract PS2/1, 2013. View the abstract on the conference website.

Schultze A et al. Prevalence of detected drug resistance across different regions of Europe: data from EuroSIDA 1997-2012. 14th European AIDS Conference, Brussels, abstract PS2/2, 2013. View the abstract on the conference website.