Research Articles from the SHS-UHN ASP (Category)

Usefulness of previous methicillin-resistant Staphylococcus aureus screening results in guiding empiric therapy for S. aureus bacteremia

AD Bai
L Burry
A Showler
M Steinberg
D Ricciuto
T Fernandes
A Chiu
S Raybardhan
GA Tomlinson
CM Bell
AM Morris



OBJECTIVES:  Staphylococcus aureus bacteremia (SAB) is an important infection.  Methicillin-resistant Staphylococcus aureus (MRSA) screening is performed in hospitalized patients to guide infectious disease control practices.  We conducted a retrospective cohort study to assess the usefulness of past MRSA screening in guiding empiric antibiotic therapy for SAB.

METHODS:  A retrospective cohort study examined consecutive patients with confirmed SAB and prior MRSA swab screening from six academic and community hospitals between 2007 and 2010.  Diagnostic test properties were calculated for MRSA swab screening in predicting methicillin susceptibility of SAB.

RESULTS:  In the study, 799 patients had MRSA screening swabs prior to SAB.  Of the 799 patients, 95 (12%) patients had a positive and 704 (88%) had a negative prior MRSA screening swab.  There were 150 (19%) patients with MRSA bacteremia.  Overall, prior MRSA screening swab had a positive likelihood ratio of 33 (CI: 18-60) and negative likelihood ratio of 0.45 (CI: 0.37-0.54).  Diagnostic accuracy differed depending on mode of acquisition (i.e. community-acquired, nosocomial, or healthcare-associated infection) (p<0.0001) and hospital (p=0.0002).  Mathematical modeling of this data demonstrates that the post-test probability of MRSA for a negative MRSA screening result is close to or below 10% when MRSA prevalence in SAB is less than 25%.

CONCLUSIONS:  MRSA screening swabs can be helpful in guiding empiric antibiotic therapy for SAB in areas with moderate MRSA prevalence.