Canadian recommendations for laboratory interpretation of multiple or extensive drug resistance in clinical isolates of Enterobacteriaceae , Acinetobacter species and Pseudomonas aeruginosa

The goal of this document was to provide Canadian laboratories with a framework for consistent reporting and monitoring of multidrug resistant organisms (MDRO) and extensively drug resistant organisms (XDRO) for common gram-negative pathogens. This is the final edition of the interim recommendations, which were modified after one year of broad consultative review. This edition represents a consensus of peer-reviewed information and was co-authored by the Canadian Public Health Laboratory Network and the Canadian Association of Clinical Microbiology and Infectious Diseases. There are two main recommendations. The first recommendation provides standardized definitions for MDRO and XDRO for gram-negative organisms in clinical specimens. These definitions were limited to antibiotics that are commonly tested clinically and, to reduce ambiguity, resistance (rather than non-susceptibility) was used to calculate drug resistance status. The second recommendation identifies the use of standardized laboratory reporting of organisms identified as MDRO or XDRO. Through the broad consultation, which included public health and infection prevention and control colleagues, these definitions are ready to be applied for policy development. Both authoring organizations intend to review these recommendations regularly as antibiotic resistance testing evolves in Canada. Affiliations 1 Health PEI, Charlottetown, PEI 2 National Microbiology Laboratory, Winnipeg, MB 3 Alberta Provincial Laboratory for Public Health, Edmonton, AB 4 Diagnostic Services Manitoba, Winnipeg, MB 5 LifeLabs, Toronto, ON 6 Cadham Provincial Laboratory, Winnipeg, MB 7 Saskatchewan Disease Control Laboratory, Regina, SK 8 Centre hospitalier universitaire Dr-Georges-L.-Dumont, Moncton, NB 9 Queen Elizabeth II Health Science Centre, Halifax, NS 10 BC Centre for Disease Control Public Health Laboratory, Vancouver, BC 11 Public Health Ontario Laboratories, Toronto, ON 12 Saskatchewan Health Authority, Regina, SK 13 Newfoundland Public Health Laboratory, St. John’s, NL 14 LifeLabs, Burnaby, BC 15 Laboratoire de santé publique du Québec, INSPQ, Ste-Anne-de-Bellevue, QC *Correspondence: michael. mulvey@canada.ca


Introduction
These recommendations were produced under the auspices and authority of the Canadian Public Health Laboratory Network (CPHLN) and the Canadian Association of Clinical Microbiology and Infectious Diseases (CACMID).They represent a consensus of peer-reviewed information and expert opinion on the most appropriate ways to define and report multidrug resistant phenotypes in common gram-negative pathogens.They build on previous interim recommendations (1) and underwent broad consultation with local, national, and international stakeholders.These recommendations are intended for use in Canadian non-veterinary clinical microbiology laboratories, and will enable standardized reporting in provincial and national surveillance programs.

Background
Antimicrobial resistance is a growing concern for human health as bacterial pathogens continue to accumulate genetic alterations conferring resistance to the antimicrobials used to treat human infections.Most concerning is the acquisition of multiple resistance traits within individual pathogens, which can greatly limit or entirely eliminate the arsenal of effective treatment options, thereby leading to poor clinical outcomes.In Canada, we have observed these highly resistant strains in Enterobacteriaceae, Acinetobacter spp.and Pseudomonas aeruginosa (2)(3)(4).
The goal of this document is to provide Canadian laboratories with a framework for consistent reporting and monitoring of multidrug resistant organisms (MDRO) and extensively drug resistant organisms (XDRO).There was a need to standardize the classification of organisms that are resistant to multiple antimicrobials in order to consistently and accurately share information locally, nationally and internationally with the medical community, public health authorities and policy makers.Additionally, classification as 'multidrug resistant' may be an actionable finding within hospital infection prevention and control programs.
The need for standardized categorization of antimicrobial resistance was recognized in 2012 by Magiorakos et al. (5), who proposed interim international definitions in selected gram-positive and gram-negative organisms.Those definitions have not yet led to revised or definitive guidelines.The recommendations in this document are based on the interim definitions proposed by Magiorakos et al. for gram-negative organisms, with modifications to better reflect the Canadian context and take into account Canadian stakeholder input.See Appendix A for more information on the methodology for developing the final recommendations as well as a description of the modifications and their justifications.Table 1 identifies the broad provincial, national, and international consultations that were conducted with the interim recommendations.
Over time, as new antimicrobials become available and currently used antimicrobials lose effectiveness or are no longer available, these definitions will require revision.The recommendations stated herein are considered final and will be reviewed every three years.

Recommendations for antimicrobial susceptibility testing
1.A resistant interpretation of an isolate can be determined using disk diffusion, broth microdilution or agar dilution following Clinical and Laboratory Standards Institute (CLSI) guidelines for susceptibility testing and interpretation of Enterobacteriaceae, P. aeruginosa and Acinetobacter spp (6).
For data harmonization, emphasis is placed on minimum inhibitory concentration (MIC) and phenotypic methods rather than expert rules providing interpretative criteria.A Health Canada-or Federal Drug Administration (FDA)-approved automated method or gradient diffusion strips can also be used for the generation of antimicrobial susceptibility data.
2. Current CLSI M100 breakpoints should be used to determine antimicrobial susceptibility of isolates (6).
Some laboratories may routinely use other breakpoint interpretations (e.g., FDA, European Committee on Antimicrobial Susceptibility Testing (EUCAST)) that differ from CLSI recommendations.Laboratories using non-CLSI breakpoints, including those using unmodified FDA-approved automated instruments, should disclose this information in their reports to provincial public health laboratories.
3. Certain species of Enterobacteriaceae should not be tested for particular antimicrobial agents because of intrinsic resistance.

Definitions
These recommendations are intended to be applied only to isolates from clinical/diagnostic specimens; however, infection prevention and control programs may choose to apply these MDRO/XDRO definitions in their antimicrobial resistant organism control activities.When reporting MDRO/XDRO isolates that are part of an asymptomatic surveillance program (e.g., inpatient admission screening), it should be clearly indicated in the laboratory report that the MDRO/XDRO classification refers to colonization or carriage status only in order to avoid unnecessary treatment.
In the following definitions, criteria using the term 'OR' should be interpreted as follows: if an isolate is resistant to either of the antimicrobial agents listed, it should be considered resistant to that criterion for the purposes of these definitions.

Acinetobacter spp. or P. aeruginosa definitions
There are no final recommendations for MDRO definitions for Acinetobacter spp. or P. aeruginosa.The previous interim recommendations for Acinetobacter spp. or P. aeruginosa MDRO status should be disregarded at this time (1).
An isolate should be considered an XDRO if it is resistant to ALL of the FIVE antimicrobial groups listed below: Table 2 provides a summary of the definitions for determining whether select gram-negative organisms are MDRO/XDRO.

Reference laboratories notification
The provincial public health laboratory should be notified of XDROs as defined above.Unlike the interim recommendations, sending of isolates is NOT requested.Referral of clinical isolates to reference laboratories should continue to occur as clinically necessary.Provincial public health laboratories will collaborate on notification and particular privacy concerns in each province.Include the following information when reporting: • Age of patient • Gender of patient • Type of clinical specimen (blood, respiratory, skin/soft tissue or urine) • Date of collection • Antimicrobial susceptibility testing results from submitting laboratory • Method and interpretive criteria used for antimicrobial susceptibility testing, as described in the recommendations above If multiple clinical isolates of the same species and susceptibility pattern are recovered from the same patient, report the isolate from the most invasive site where possible.Only one isolate of each XDRO should be reported per patient per year to the provincial laboratory.
The provincial public health laboratory as defined in Appendix B will report all of the data to the National Microbiology Laboratory (NML).The NML will compile and enable distribution of national surveillance reports to contributing laboratories and provincial public health authorities on an annual basis.

Table 1 :
Provincial, national and international organizations consulted on the interim guidelines

Table 1 :
Provincial, national and international organizations consulted on the interim guidelines (continued) Abbreviation: GNB, gram-negative bacilli An isolate should be considered a MDRO if it is resistant to THREE OR FOUR of the SIX antimicrobial groups listed below: • Tobramycin OR gentamicin (see exceptions for Serratia spp. in Table 2) • Piperacillin-tazobactam • Imipenem OR meropenem (see exceptions for Proteus spp. in Table 2) • Cefotaxime OR ceftriaxone OR ceftazidime • Ciprofloxacin • Trimethoprim-sulfamethoxazole An isolate should be considered an XDRO if it is resistant to FIVE OR SIX of the SIX antimicrobial groups listed above.

Table 2 :
Definitions for the determination of MDRO/XDRO in select organisms MDRO, multidrug resistant organisms; XDRO, extensively drug resistant organisms a The term 'OR' should be interpreted as follows: if an isolate is resistant to either antimicrobial agent listed, it should be considered resistant to that criterion for the purposes of these definitions b Resistance in Serratia spp.should only consider gentamicin susceptibility testing results c Resistance in Proteus spp.should only consider meropenem susceptibility testing results d Resistance in P. aeruginosa may include piperacillin-tazobactam OR piperacillin.For all Acinetobacter spp.piperacillin-tazobactam must be used