Poster Presentation Australian Diabetes Society and the Australian Diabetes Educators Association Annual Scientific Meeting 2017

POSTER DISCUSSION: Microbiology results reveal antimicrobial stewardship opportunities amongst a Multidisciplinary Diabetic Foot Unit (MDFU) inpatient cohort (#225)

Robert Hand 1 , Paul Ingram 2 3 , Lydia Lamb 4 , Dipen Sankhesara 1 , Tina Dilevska 5 , Erica Ryan 6 , Ashley Makepeace 4 , Carsten Ritter 5 , Laurens Manning 3 , Emma J Hamilton 4 7
  1. General Medicine, Fiona Stanley Hospital, Perth, WA, Australia
  2. Microbiology Department, Pathwest, Fiona Stanley Hospital, Perth, WA, Australia
  3. Infectious Diseases Department, Fiona Stanley Hospital, Perth, WA, Australia
  4. Endocrinology Department, Fiona Stanley Hospital, Perth, WA, Australia
  5. Vascular Surgery Department, Fiona Stanley Hospital, Perth, WA, Australia
  6. Podiatry Department, Fiona Stanley Hospital, Perth, WA, Australia
  7. Fiona Stanley Hospital, Murdoch, WA, Australia

Background

Empiric antimicrobial regimes for diabetic foot infections (DFI) vary according to local epidemiology and prior colonisation/infection with resistant pathogens.  The utility of using results from culture of superficial swabs to guide empiric antibiotic therapy is not well established in Australia, particularly in the context of rising prevalence of drug resistant organisms.  Antibiotic resistance is an emerging threat to DFI management.

Aims

To assess the utility of DFI microbiology results and their relationship to empiric antibiotic prescribing.

Methods

Retrospective observational study of 151 admissions in 128 patients admitted to Fiona Stanley Hospital MDFU from 1st February 2015 to January 31st 2016.

Results

The mean age was 60.4±14.9 years, 11.7% were Indigenous Australians.  Most admissions (92%) were for moderate or severe DFI.  Empiric antibiotic prescribing was consistent with published guidelines.  Of those with positive cultures, 85% were polymicrobial. Dominant pathogens included: S. aureus (48%), beta-hemolytic streptococci (24%), Enterobacteriaceae (15%), enterococci (8%) and Pseudomonas (6%). Excluding cultures of known skin commensals, the proportion of superficial cultures concordant with deep tissue or blood cultures ranged from 0% (Pseudomonas) to 50% (Enterobacteriaceae).  Prior colonization with methicillin resistant S. aureus (MRSA) or vancomycin resistant enterococci (VRE) occurred in 12% and 8% patients respectively.  Prior MRSA colonization had a positive predictive value (PPV) of 52% and negative predictive value (NPV) of 97%, previous VRE colonization had a PPV of 0% and NPV of 100% for inpatient infection. Overprescribing with anti-MRSA and/or anti-pseudomonal agents occurred commonly (76%) given subsequent culture results, however empiric prescribing provided insufficient antimicrobial activity in 12%.

Conclusion

Cultures of superficial swabs correlated poorly with deep tissue or blood cultures.  Knowledge of absence of prior MRSA colonization provides justification to withhold empiric anti-MRSA therapy. Broad spectrum empiric therapy may not be necessary in this setting, highlighting opportunities for rationalization of antimicrobial therapy.