Screening methods for meticillin-resistant Staphylococcus aureus

The UK National External Quality Assessment Service (UK NEQAS) distributes clinically relevant and educational specimens for external quality assessment (EQA). The aim of this report was to assess the suitability of using a freeze-dried specimen format for the EQA of conventional and rapid methods and to review the methods used by participants to screen for meticillin-resistant Staphylococcus aureus (MRSA). Of the 714 laboratories that returned a result, 678 reported the presence of MRSA, and results showed a mean of 73 c.f.u. per 25 ml and a median of 50 c.f.u. per 25 μl confirming that the specimen was homogeneous. Four different approaches to MRSA screening were used routinely, including: (i) liquid culture; (ii) direct plating onto conventional media; (iii) direct plating onto chromogenic media; and (iv) rapid methods. A wide variety of methods were used within each of these four categories to screen for MRSA, and many laboratories reported using more than one method. Attempts should be made to determine the most appropriate approach to MRSA screening and to standardize the protocols across the UK.