Infected Diabetic Foot Ulcer

Infected diabetic foot ulcer is a diabetic foot wound with clinical evidence of bacterial infection. Infection is the commonest cause of hospital admission and lower limb amputation in people with diabetes.

• Organisms: Staphylococcus aureus and streptococci (acute, superficial); polymicrobial with gram negatives (Enterobacterales, Pseudomonas) and anaerobes in chronic or deep disease; MRSA in some.
• Predisposing factors: neuropathy, ischaemia, callus, poor glycaemic control, previous ulcer, renal disease, HIV.

At least two of: local swelling or induration, erythema over 0.5 cm around the wound, tenderness, warmth, purulent discharge.

• Grading: mild (superficial, erythema 0.5 to 2 cm, no systemic features); moderate (erythema over 2 cm, or deep structures involved, without systemic response); severe (with fever over 38 degrees Celsius, heart rate over 90, respiratory rate over 20, white count over 12 or under 4 x 10^9/L).
• Foul smell, gas, necrosis, exposed bone or probe to bone positive suggests osteomyelitis; painless in neuropathy.
• Differential diagnosis: Charcot neuroarthropathy, gout, venous stasis, deep vein thrombosis, necrotising fasciitis, arterial ischaemia, pressure injury, cellulitis from other cause, osteomyelitis.
• Complications: deep abscess, necrotising infection, osteomyelitis, septic arthritis, gangrene, sepsis, amputation, death.

Clinical diagnosis with microbiology and imaging.

• Deep tissue or bone culture after debridement (surface swabs are unreliable); blood cultures if febrile.
• Full blood count, CRP, ESR (over 70 mm/h suggests osteomyelitis), glucose, HbA1c, creatinine, lactate.
• Plain radiograph; MRI for abscess and osteomyelitis; ankle brachial index and toe pressures, duplex or CT angiography for perfusion.

Drain and debride early, give antibiotics by severity, restore perfusion and control glucose.

• Supportive: admit moderate and severe infection, bed rest or complete offloading, insulin to maintain glucose 6 to 10 mmol/L, fluids, analgesia (paracetamol 1 g, amitriptyline for neuropathic pain), nutrition, smoking cessation, tetanus toxoid if needed.
• Pharmacological: mild: amoxicillin clavulanate 625 mg three times daily or cefalexin 500 mg four times daily for 7 days (clindamycin 300 mg four times daily if penicillin allergic); add doxycycline 100 mg twice daily or cotrimoxazole 960 mg twice daily if MRSA is suspected. Moderate: amoxicillin clavulanate 1.2 g IV every 8 hours, or ceftriaxone 2 g IV daily with metronidazole 500 mg IV every 8 hours, for 7 to 14 days. Severe: piperacillin tazobactam 4.5 g IV every 6 hours (or meropenem 1 g IV every 8 hours for ESBL organisms) plus vancomycin 15 to 20 mg/kg IV every 12 hours (or linezolid 600 mg twice daily), adjusted by culture; add ciprofloxacin 750 mg twice daily if Pseudomonas. Osteomyelitis: 6 weeks of targeted therapy without surgery, or 2 to 5 days after complete resection of infected bone with clean margins. Switch to oral therapy when stable. Adjust doses to renal function.
• Procedures: urgent incision, drainage and debridement of abscess, necrotic tissue and infected bone; revascularisation when toe pressure is under 30 mmHg or ankle brachial index under 0.5; amputation for gangrene, uncontrolled sepsis or non salvageable limb; negative pressure therapy once infection is controlled.
• Special groups: renal impairment, adjust antibiotic doses and avoid nephrotoxins; pregnancy, avoid fluoroquinolones, doxycycline and trimethoprim; HIV, antiretroviral therapy and tuberculosis screen; elderly, geriatric review and early nutrition.
• Red flags: fever and rigors, hypotension, crepitus, rapidly spreading erythema, wet gangrene, severe ischaemic pain, ketoacidosis, exposed bone, no response at 48 to 72 hours.
• Follow-up: daily review while admitted; wound review weekly; ESR and CRP every 1 to 2 weeks in osteomyelitis; custom footwear and podiatry for life.