Assessment of laboratory performance with Streptococcus pneumoniae antimicrobial susceptibility testing in the United States - A report from the College of American Pathologists Microbiology Proficiency Survey Program

Objective.-To assess the performance of clinical microbiology laboratories in the United States when conducting in vitro susceptibility tests with Str eptococcus pneumoniae. Methods.-The results of a nationwide College of American Pathologists Profi ciency Survey test sample, in which susceptibility testing of an isolate of S pneumoniae was performed, were assessed with respect to precision and ac curacy. Results.-Wide variability was noted among participating laboratories with b oth minimum inhibitory concentration procedures and disk diffusion suscepti bility tests when both methods were applied to S pneumoniae. Despite this h igh degree of variation, categorical interpretive errors were uncommon. Num erous laboratories reported results for antimicrobial agents that ape not r ecommended by the National Committee for Clinical Laboratory Standards for tests with S pneumoniae. Conclusions.-Current susceptibility testing practices with S pneumoniae in the United States indicate limited precision and a tendency for laboratorie s to test and report results obtained with antimicrobial agents of question able therapeutic value against this organism. Continued efforts to standard ize susceptibility testing of S pneumoniae in the United States are warrant ed. In addition, modifications of existing interpretive criteria may be nec essary.