Many different definitions for multidrug-resistant (MDR), extensively-drug resistant (XDR) and pandrug-resistant (PDR) bacteria are being used in the medical literature to characterize the different patterns of resistance found in healthcare-associated, antimicrobial-resistant bacteria.  Harmonized definitions with which to describe and classify bacteria that are resistant to multiple antimicrobial agents are needed, so that epidemiological surveillance data can be reliably collected and compared across healthcare settings and countries.

A group of international experts came together by a joint initiative by the European Centre for Disease Prevention and Control (ECDC) and the Centers for Disease Control and Prevention (CDC), to create a standardized international terminology with which to describe acquired resistance profiles in Staphylococcus aureus, Enterococcus spp., Enterobacteriaceae (other than Salmonella and Shigella), Pseudomonas aeruginosa, and Acinetobacter spp., all bacteria often responsible for healthcare-associated infections and prone to multidrug resistance.

By applying these definitions, clinical, reference and public health microbiology laboratories will use a common terminology for grading various antimicrobial resistance profiles. This will result in consistent reporting of comparable data that can reliably track trends of antimicrobial resistance locally, but also internationally.

Definitions:

The definitions are published in Clinical Microbiology and Infection and are openly accessible at: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2011.03570.x/pdf
Updates of the definitions will, when performed, be posted on this webpage hosted by ECDC.

Tables:

To promote diffusion and use of the definitions in practice, all tables included in the document are also available as worksheets that can be downloaded below. These include:

• The antimicrobial categories and agents used to define MDR, XDR and PDR isolates for various bacteria (Tables 1-5);
• The definitions themselves (Table 6) as well as one example of how the antimicrobial susceptibility profile for a P. aeruginosa isolate would look if it is MDR, XDR or PDR (Table 7).