Performance of Canadian clinical laboratories processing throat culture proficiency testing surveys

Proficiency testing results obtained from simulated throat swab cultures sent between 1999 and 2013 were analyzed to evaluate the ability of participants to process, analyze, and properly report results for these cultures. Eight percent of all pathogen-positive samples were reported as false negatives, and 11 % of the pathogen-negative ones were reported as false positives. More than 90 % of the participants achieved acceptable grades in each of the proficiency testing samples containing Streptococcus pyogenes. Laboratories were less successful in reporting other significant pathogens including group C and G streptococcus and Arcanobacterium haemolyticum, although an overall increase in performance was observed for each subsequent survey. Most laboratories recognized other respiratory pathogens as not being agents of pharyngitis; a common issue with these specimens was the suggestion of the organism’s clinical significance when their presence was reported. The presence of small colony-forming β-hemolytic streptococcus (Streptococcus anginosus group) proved to be challenging for many laboratories as 66 % of all unacceptable grades for pathogen-negative throat swabs occurred in these PT samples. Moreover, performance in this group did not improve with subsequent surveys. Results obtained in this study support the added value of clinical relevancy challenges for proficiency testing as laboratories that may not have problems with the analytical aspect of the testing process struggle with the appropriate interpretation of results.