This paper describes the results of second-line drug (SLD) susceptibility tests among multidrug-resistant tuberculosis (MDR TB) cases reported in 20 European countries aiming to identify extensively drug-resistant tuberculosis (XDR TB) cases. A project on molecular surveillance of MDR TB cases was conducted by EuroTB and the National Institute for Public Health and the Environment (RIVM) from 2005 to 2007. Information on drug susceptibility testing (DST) was provided to this project and case-based data on MDR TB cases were reported on a quarterly basis by 20 countries of the World Health Organization s European Region, including 15 European Union Member States. Data included SLD susceptibility test results, enabling a retrospective description of XDR TB cases notified between 2003 and 2007 .In 18 countries DST was performed for two or more of the SLD included in the XDR TB definition. The proportion of MDR TB isolates tested for SLD varied widely between countries (range 20 to 100 percent). In the 18 countries, 149 (10%) XDR TB cases were reported among MDR TB cases with available DST results for SLD. Sixteen additional MDR TB cases were reported by the MDR TB surveillance system when compared with the number of routinely reported MDR TB cases to EuroTB in ten countries with representative data reported during three consecutive years (2003-2005). To counter the threat of XDR TB in Europe, a standardised approach to XDR TB surveillance and DST for SLD is needed, as well as increased laboratory capacity across European countries
