Meticillin-resistant Staphylococcus aureus Contact Screening Strategy in a Low Prevalence Setting; a Nested Case-Control Study()

BACKGROUND: The optimal screening strategy in hospitals to identify secondary cases after contact with a meticillin-resistant Staphylococcus aureus (MRSA) index patient in a low prevalence setting is not well defined. We aimed at identifying factors associated with documented MRSA transmissions. METHOD: Single center, retrospective, nested case-control study. We evaluated the screening strategy in our 950 bed tertiary care hospital from 2008 – 2014. Room and ward contacts of MRSA index patients present at time of MRSA identification were screened. We compared characteristics of Staphylococcus aureus Protein A (spa)-type matched contact patients (cases) to negative or spa-type mismatched contact patients (controls). RESULTS: Among 270,000 inpatients from 2008 – 2014, 215 MRSA screenings yielded 3013 contact patients, and 6 (0.2%) spa-type matched pairs. We included 225 controls for the nested case-control study. The contact type for the cases was more frequently “same room” and less frequently “same ward” compared with the controls (P = 0.001). Also, exposure time was longer for cases (median of 6 days [IQR 3–9]) than for controls (1 day [0–3], P=0.016). CONCLUSION: The extensive MRSA screening strategy revealed only few index/contact matches based on spa-typing. Prolonged exposure time and a shared room were significantly associated with MRSA transmission. A targeted screening strategy may be more useful in a low prevalence setting than screening entire wards.