Penicillin-resistant Streptococcus pneumoniae. Report of a case and results of a clinical laboratory proficiency survey in Minnesota

An elderly woman with Streptococcus pneumoniae meningitis relatively resistant (minimum inhibitory concentration, [MIC] = 0.12 μg/mL) to penicillin is reported. The occurrence of penicillin-resistant pneumococcal infections is reviewed and management discussed. Because of the importance of recognition of resistant pneumococci, a state-wide clinical laboratory survey was conducted to determine the accuracy of susceptibility testing for this isolate. Of 111 laboratories completing the survey, only 26 performed the 1-μg oxacillin disk test as recommended by the National Committee for Laboratory Standards (NCCLS). When laboratories were analyzed according to hospital size, the proficiency in performing the proper susceptibility testing was 55% (6 of 11) for hospitals with more than 400 beds versus 3% (2 of 58) for hospitals with fewer than 100 beds (P < 0.0001 by Fisher's exact test). This contrasts with reported surveys by the College of American Pathologists (CAP), and reasons for this are explored. Guidelines for laboratory testing of S. pneumoniae are reviewed, and additional study of clinical proficiency with attention to laboratory size is recommended.