169. Penicillin-susceptible Staphylococcus aureus (PSSA) infection in an era of multidrug-resistance
Session: Poster Abstract Session: Diagnostic Microbiology
Thursday, October 18, 2012
Room: SDCC Poster Hall F-H
Background: It is commonly stated that 5% of methicillin-susceptible Staphylococcus aureus (MSSA) isolates are sensitive to penicillin (P); one reference notes that, “rare isolates remain penicillin susceptible”. [1] Lab guidelines recommend that P should not be reported as sensitive unless confirmed with inducible beta-lactamase testing; some labs do not test or report P because of the notion that clinicians do not use the drug. We sought to characterize the frequency of serious infections caused by PSSA and to examine how clinicians are managing these patients.

Methods: All patients with Staphylococcus aureus (SA) in blood cultures from July - December 2011 were selected from the Kaiser Regional Reference Lab database; repeat episodes were excluded. A retrospect chart review was performed.

Results: There were 445 patients with one or more positive blood cultures for SA; 165 had methicillin-resistant SA (37%). Among the 280 patients with MSSA, 58 were identified as PSSA (20%); two were <18 yrs old and were excluded. Mortality among adults with PSSA bacteremia during the index hospitalization was 14%. Eight patients received broad spectrum antibiotics when cultures of other sites grew bacteria other than SA or if they died before the sensitivity was available; these were also excluded. The remaining 48 patients were treated as follows: P in 6 (12.5%), oxacillin/nafcillin in 9 (18.8%), cefazolin in 12 (25%), ceftriaxone in 8 (16.7%), vancomycin in 2 (4.2%). Seven of the regimens were considered inappropriate (14.6%) which included oral cephalexin/dicloxacillin (2), ciprofloxacin/moxifloxacin (3) and vancomycin (in the absence of allergy, 2). P allergy was documented in 8 of 56 adults.

Conclusion: The rate of serious SA infection caused by PSSA may be increasing and hence labs should continue to report P sensitivity. However, after accounting for allergy only 6 of 40 patients with PSSA monomicrobial bacteremia received P (15%) even though P is considered the drug of choice. The majority of patients received another beta-lactam as primary therapy (57.5%) but a sizable number (15%) received inappropriate or inadequate therapy. In this era of increasing drug resistance, clinicians should reconsider utilizing P when treating patients with serious PSSA infection.

[1] Johns Hopkins ABX Guide, accessed 4/3/12

Jared Goodman, MD, Internal Medicine, Kaiser Permanente, Los Angeles, CA and Jim Nomura, MD, Kaiser Permanente, Los Angeles, CA


J. Goodman, None

J. Nomura, None

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