We retrospectively studied 306 pediatric methicillin-resistant Staphylococcus aureus isolates collected in 2000/2001, 2003, 2005, and 2007 for possible vancomycin minimum inhibitory concentration (MIC) change over time using Etest, agar dilution, and broth microdilution (MicroScan) methods. Vancomycin MICs did not increase. Inducible clindamycin resistance declined significantly (53%-0%, P < 0.001). Considerably different proportions of isolates with vancomycin MIC = 2 microg/mL were identified by different laboratory methodologies, suggesting the need for caution in their interpretation and in comparing published data. During this period the proportion of USA300 strains increased dramatically.

A total of 120 pleural fluid specimens from 113 pediatric patients were tested using two rapid antigen detection assays for Streptococcus pyogenes. Results were compared to culture, Gram stain, and PCR results. Each rapid antigen assay detected 9 out of 10 (90%) PCR-positive samples, with 100% specificity. These antigen detection assays are useful to provide microbiological diagnosis of empyema caused by S. pyogenes.