Background: The National Microbiology Laboratory (NML), Public Health Agency of Canada conducts ongoing monitoring of antimicrobial susceptibilities in Neisseria gonorrhoeae. To standardize the susceptibility testing data and maintain the comparability of data generated from each province in Canada, the NML offers a proficiency testing program conducted two times a year.
Methods: Eight provincial public health laboratories from across Canada participated in 10 proficiency panel distributions between 2008 and 2012. Control strains included a combination of 4 of the following isolates: WHO B, WHO C, WHO F, WHO K, ATCC 49226. Each distribution included 5 N. gonorrhoeae test isolates. Minimum inhibitory concentrations (MICs) were determined using either the agar dilution testing method or the Etest method. MIC interpretations were based on the criteria of the Clinical Laboratory Standards Institute (CLSI) and the World Health Organization (WHO) criteria for decreased susceptibility to cephalosporins.
Results: A total of 90 isolates, including control strains and test isolates were included from 2008 to 2012. The overall agreement of MIC results (MICs±1 log2 dilutions) between all laboratories when compared to the calculated modal MICs was 95.1% (4,243/4,462). Percentage agreements between agar dilution and Etest MIC results were calculated for all strains tested by all laboratories during this time with the following results: penicillin, 100% (51/51); spectinomycin, 98.4% (61/62); tetracycline, 82.3% (56/68); ceftriaxone, 93.1% (54/58); ciprofloxacin, 96.7% (58/60); cefixime 100% (23/23); and azithromycin 98.5% (67/68); erythromycin, 100% (28/28).
Conclusions: Laboratories participating in this proficiency testing program achieved a degree of correlation of greater than 95% for antimicrobial susceptibility testing results. Participating in a proficiency testing program is beneficial to each laboratory as possible discrepancies in results are identified giving each laboratory the opportunity to improve testing protocols. This contributes to improved quality of results and leads to better quality patient care and public health prevention programs.