( ntact precautions for colonized or infe...)Controlling the Spread of Healthcare Associated Methicillin Resistant Staphylococcus aureus Requires Active Surveillance,Health

Although screening for colonization with MRSA is of major importance in limiting its nosocomial spread, the standard techniques for MRSA detection, including molecular biology based methods, have required a culture step and isolation of pure colonies. Culture and selection of pure colonies entail a high level of technical training and judgment and may take up to 96 hours for results.

In 2004 two screening methods for the direct detection of nasal colonization by MRSA were approved for marketing in the US by the FDA. Both methods are performed on nasal swab specimens. A third method for direct MRSA detection on nasal swabs is in the final stages of development in the United Kingdom, and is projected for launching in the UK in the second quarter of 2005.

BBL CHROMagar MRSA (BD Diagnostics), utilizes culture on a selective and differential medium. The nasal swab specimen is directly inoculated to the plate for streaking and the plates are incubated for 24 to 48 hours. The agar permits the direct detection and identification of MRSA through the incorporation of specific chromogenic substrates and cefoxitin. MRSA colonies appear mauve on the chromagar, whereas other colonies are either inhibited or produce a distinctly different color. In a nasal swab surveillance study the manufacturer reports a sensitivity and specificity of 95.7% and 97%, respectively, when compared to the gold standard of PCR detection of the mecA gene. In an independent clinical evaluation, Flayhart et al reported a sensitivity and specificity of 99.5% and 98% respectively, when clinical samples were tested on CHROMagarTM and compared to culture on conventional media.

IDI-MRSA (Infectio Diagnostic, Inc.), utilizes PCR for the amplification of MRSA DNA and fluorogenic target-specific hybridization probes for the detection of the amplicons. Nasal swab specimens are placed directly in sample preparation b
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