Background: Guidelines suggest that patients on continuous antiretroviral therapy for >4 months with current viral load (VL)>1,000 copies/ml should be tested for resistance. There are limited data showing the frequency of resistance testing in routine clinical practice following these recommendations.

Methods: In EuroSIDA, virological failure (VF) was defined as confirmed VL>1,000 copies/ml after =4 months continuous use of any antiretroviral in a =3-drug regimen started during or after 2002. We assessed whether a resistance test was performed around VF (from 4 months before to 1 year after VF) and used logistic regression analysis to assess factors associated with having a resistance test.

Results: A total of 1,090 patients experienced VF a median 8.1 months (range 4 months to 6.3 years) after starting their regimen. There were 395 (36.2%; 95% CI 33.4–39.1) patients with a resistance test around the time of VF. Predictors of having a resistance test following VF include availability of a resistance test earlier than 4 months before VF (OR 2.20, 95% CI 1.77–2.75 for yes versus no; P<0.0001), region (OR 0.29, 95% CI 0.14–0.62 for Eastern Europe versus Northern Europe and OR 0.64, 95% CI 0.48–0.85 for Southern Europe versus Northern Europe; global P=0.0006) and current calendar year (OR 0.45, 95% CI 0.30–0.68 for =2007 versus 2004; global P=0.003).

Conclusions: This analysis suggests a delay in genotypic testing after VF that seems longer than expected given current treatment guidelines. This delay is highly variable across Europe.