MRSA admission screening in a low prevalence setting - much ado about nothing?

OBJECTIVE To prospectively evaluate new guidelines for MRSA admission screening and pre-emptive isolation implemented in response to a doubling of newly diagnosed MRSA patients in 2007. DESIGN One-year surveillance (04/2008-03/2009). SETTING Patients admitted to the tertiary-care hospital in St. Gallen (700 beds) and 10 affiliated public hospitals (890 beds) in Eastern Switzerland (MRSA rate 2.5% in isolates). PATIENTS Except for known MRSA carriers, all patients who underwent admission screening in accordance with the guidelines and all MRSA patients newly detected by a clinical sample were included. METHODS Depending on epidemiological factors (stay in a foreign hospital, a Swiss hospital with known high MRSA prevalence, or a chronic care facility) and personal risk factors (wound, tracheostoma, urinary catheter, IVDU), patients were risk stratified into screening and isolation, only screening or no screening at all. MRSA admission screening included nasal, throat and axillary/inguinal swabs, supplemented by wound swabs, urine and respiratory secretion whenever appropriate (conventional culture). RESULTS A total of 6/161 (3.7%) MRSA admission screenings yielded positive results (number needed to screen: 27). 2/32 (6.3%) pre-emptively isolated patients were positive (number needed to isolate: 16). Only 6/27 (22.2%) newly diagnosed MRSA patients were detected by admission screening, and the remaining patients were detected by clinical sample during hospitalisation. A total of 80% of the MRSA positive patients had wounds. Swabs of axilla/inguina did not increase the sensitivity of the admission screening. CONCLUSIONS In the setting of low MRSA prevalence, admission screening of patients at high risk for MRSA carriage detected only one out of five newly diagnosed MRSA patients, emphasising the importance of standard precautions for the prevention of MRSA transmission.