1591. Fosfomycin Resistance is Associated with Receipt of Incorrect Empiric Therapy for Multidrug Resistant Uropathogens
Session: Poster Abstract Session: Multidrug-Resistant Gram Negative Rods
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
Background: Increasing rates of multi-drug resistant (MDR) and extended-spectrum beta-lactamase (ESBL) uropathogens have resulted in few oral choices for empiric treatment of UTI. Fosfomycin (FOS) has been shown in previous surveys to be active against 85-100% of MDR pathogens. However routine susceptibility testing is not available and little is known about risk factors for predicting FOS resistance, which could result in choosing incorrect empiric therapy.  We sought to determine the prevalence of and risk factors for fosfomycin-resistant (FOS-R) ESBL uropathogens from 2011-2013. 

Methods: We evaluated a collection of ESBL uropathogens from 2 VA hospitals for FOS-R using disk diffusion and standard published breakpoints. The electronic health record was reviewed to capture risk factors, antimicrobial use, and outcomes.

Results: Among 91 ESBL uropathogens, 17 (18.7%) were FOS-R.  Klebsiella was more likely to be FOS-R than E. coli (46% vs. 6.3%, p <.001). Chart review was performed on 62 unique episodes. FOS-R was independently associated with urinary catheterization (p=0.04) and prior urinary tract infection (p=0.02). Compared to patients with FOS-S uropathogens, patients with FOS-R uropathogens were more likely to receive IV therapy with a beta-lactam or carbapenem (75% FOS-R vs. 37% FOS-S, OR = 5.1, p = .02) and to receive inactive empiric therapy (62% vs. 32%, OR = 3.3, p =0.07). Co-resistance with FOS was present in 20% (10/50) of fluoroquinolone-R ESBL uropathogens, 16% (6/37) of bactrim-R uropathogens, and 35% (8/23) of nitrofurantoin-R uropathogens.  Of the 11 ESBL isolates resistant to all 3 oral agents (FQ, TS, NF), 9 remained susceptible to FOS.  Only 2/62 (3.2%) ESBL uropathogens were resistant to all oral agents.

Conclusion: FOS remains active against a majority of ESBL uropathogens, although our rates of resistance are higher than previous studies.  Co-resistance with oral agents varied and was greatest with nitrofurantoin resistance. The majority of uropathogens remained susceptible to at least one available oral agent.  FOS-R can be anticipated in patients with Klebsiella, previous UTI, or urinary catheterization. Inactive empiric therapy is more likely among patients with FOS-R and warrants further investigation.

Katherine Linsenmeyer, MD1, Judith Strymish, MD2,3, Susan Weir, MPH, PhD1,2, Gretchen Berg2, Stephen Brecher, PhD2 and Kalpana Gupta, MD, MPH1,2, (1)Department of Medicine/Boston University School of Medicine, Boston, MA, (2)VA Boston HCS, West Roxbury, MA, (3)Medicine, Harvard Medical School, Boston, MA


K. Linsenmeyer, None

J. Strymish, None

S. Weir, None

G. Berg, None

S. Brecher, None

K. Gupta, None

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