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.
To assess the utility of DFI microbiology results and their relationship to empiric antibiotic prescribing.
Retrospective observational study of 151 admissions in 128 patients admitted to Fiona Stanley Hospital MDFU from 1st February 2015 to January 30th 2016.
The mean age of patients was 60.4±14.9 years, 11.7% were Indigenous Australians. Ninety-two percent of admissions were moderate or severe DFI. The DFI's culturing Streptococcus, 97% were moderate or severe. 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 for Streptococcal species ranged from 0-41% compared with 21% for S. Aureus. Streptococcal bacteraemia occurred on 3 admissions. Despite following antibiotic prescribing guidelines, overprescribing with anti-MRSA and/or anti-pseudomonal agents occurred commonly (76%), however empiric prescribing provided insufficient antimicrobial activity in 12%.
Streptococcus remain a common cause of diabetic foot infections. Superficial swabs results correlated poorly with deep tissue or blood cultures. Local knowledge regarding causative organisms may allow for reduction in broad spectrum empiric antibiotic therapy, minimizing the development of resistant organisms.