Diabetic Foot Infection Dr David Orr Consultant Microbiologist Lancashire Teaching Hospitals
History of previous amputation [odds ratio (OR)=19.9, P=.01],
Peripheral vascular disease (OR=5.5, P=.007)
Peripheral neuropathy (OR 3.4, P=.044).
Diagnosing diabetic foot infection At least 2 of the following items: Local swelling or induration Erythema Local tenderness or pain Local warmth Purulent discharge (thick, opaque to white or sanguineous secretion)
Grading Diabetic foot infections PEDIS Perfusion Extent Depth Infection Sensation
PEDIS grade 1 No symptoms or signs of infection
PEDIS grade 2 Local infection only involving skin and softtissue No systemic signs Erythema 2cm around the ulcer
PEDIS grade 3 Local infection with > 2 cm erythema around ulcer or involving structure deeper than the skin (e.g. bone, abscess) No systemic feature of infection
PEDIS grade 4 Local infection plus signs of sepsis 2 of Temp < 36 or >38 Pulse >90 Respiratory rate >20 White cell count <4 or >12
All chronic wounds contain micro-organisms
Wound colonisation The presence of replicating micro-organisms adherent to the wound in the absence of injury to the host For example Staphylococcus epidermidis Corynebacterium species (diptheroids)
Wound infection The presence of replicating micro-organisms within a wound with subsequent host injury. Leads to A non-healing wound Local invasion Systemic dissemination
Infection = Dose of Bacteria x Virulence Host Resistance
Host resistance Local Factors Large area Deep Foreign body Necrotic tissue Reduced perfusion Systemic factors Malnutrition Diabetes Alcoholism Corticosteriods Immunosuppressive
Spectrum of Organism Virulence Low Medium High S.albus Diptheroids Coliforms Anaerobes - Bacteroides Pseudomonas aeruginosa Clostridium perfringens S.aureus Group A ß haemolytic Strep
What makes an organism Virulent? Combination of virulence factors e.g. Gp A ß haemolytic Streptococci Toxins - Hyaluronidase Leucocidin Streptolysin Streptokinase Capsule - Antiphagocytic Adhesins
Virulence and the infecting dose Levels of greater than 10 5 CFU per gram of tissue is generally regarded as the cut off However -haemolytic Streptococci at 10 2 to 10 3 CFU can induce significant host injury Many wounds with greater than 10 5 CFU/g heal without incident
Techniques for assessing wound infection Quantitative biopsy (cut-off 10 5 CFU/g) - gold standard Quantitative swab (cut-off 10 5 CFU/cm 2 ) Rapid slide technique Aspiration Semi-quantitative swab (3+ or more growth)
Alternative cultures for comparison included, cultures derived from needle aspiration, wound base biopsy, deep tissue biopsy, surgical debridement, or bone biopsy
Common laboratory reports what does it mean?
Empiric treatment of diabetic foot infections PEDIS Antibiotic Suggested empiric agents Grade Spectrum Uninfected N/A N/A 1 Infection present: at least 2 of: local signs of swelling or pain/tenderness or warmth or erythema, or purulent discharge 2 Gram positive Flucloxacillin 1g QDS PO cocci (GPC) or if penicillin allergy: Clindamycin 450mg QDS PO Up to 14 day course
PEDIS Grade Antibiotic Spectrum 3 GPC, aerobic Gram negative bacilli (GNB) anaerobes Suggested empiric agents Flucloxacillin IV 2g QDS + Gentamicin IV 5mg/kg IDBW OD (max dose 500mg) + Metronidazole PO 400mg TDS If penicillin allergy (rash): Cefuroxime IV 1.5g TDS + Metronidazole PO 400mg TDS If penicillin anaphylaxis or MRSA: Teicoplanin IV 10mg/kg OD + Gentamicin IV 5mg/kg IDBW OD (max dose 500mg) + Metronidazole PO 400mg TDS For OPAT use: Ceftriaxone 2g OD + Metronidazole PO 400mg TDS If penicillin anaphylaxis or MRSA: Teicoplanin IV 10mg/kg OD + Metronidazole PO 400mg TDS + Ciprofloxacin 500mg BD (please check drug interactions)
PEDIS Grade Antibiotic Spectrum 4 GPC, aerobic Gram negative bacilli (GNB) (especially if chronic/previous antibiotics) anaerobes (especially if necrosis / ischaemia) Suggested empiric agents Flucloxacillin IV 2g QDS + Gentamicin IV 5mg/kg IDBW OD (max dose 500mg) + Metronidazole PO 400mg TDS or if penicillin allergy (rash): Cefuroxime IV 1.5g TDS + Metronidazole PO 400mg TDS If penicillin anaphylaxis or MRSA: Teicoplanin IV 10mg/kg OD + Gentamicin IV 5mg/kg IDBW OD (max dose 500mg) + Metronidazole PO 400mg TDS
Diagnosing Diabetic Foot Osteomyelitis Probe-to-bone test Plain radiographs Often serial exam MRI scanning Leukocyte or antigranulocyte scan Diagnostic bone biopsy
Diabetic Foot Osteomyelitis Common pathogens
Sampling 2-week antibiotic-free period Biopsy access preferably traversing unaffected skin Preferably performed under imaging guidance
Duration of treatment
Antimicrobial wound dressings IDSA Not recommended by IDSA because - Evidence for benefit lacking Cost Concerns over Resistance
If you are going to use topical antimicrobials Avoid ones which are also given systemically Gentamicin, Tobramycin, Fusidic acid, Quinolones Avoid common allergens Neomycin,?bacitracin Avoid agents which have high cellular toxicity Chlorhexidine, hydrogen peroxide,? Povidone iodine, Perhaps consider- Silver sulfadiazine Cadexomer/slow release forms of iodine
Questions? Together we can make a difference