Background
An expert panel from the Infectious Diseases Society of America recently published an update to the guideline for the diagnosis and treatment of diabetic foot infections (DFIs).
Conclusions
With the rising incidence of diabetes mellitus, DFIs are an increasingly common complication with potentially serious sequelae. DFIs typically begin in a wound, most often a neuropathic or traumatic ulceration. Infection is defined by at least two classic findings of inflammation (redness, warmth, swelling/induration, and pain/tenderness) or purulence. Other signs of infection are friable or discolored granulation tissue, undermining of wound edges, and foul odor.
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An expert panel from the Infectious Diseases Society of America recently published an update to the guideline for the diagnosis and treatment of diabetic foot infections (DFIs).
DFIs are classified into mild (superficial and limited in size), moderate (deeper or more extensive), or severe (accompanied by systemic signs or metabolic perturbations).
Factors associated with increased risk of infection include a positive probe-to-bone test, ulcer duration longer than 30 days, traumatic wound, presence of peripheral vascular disease or peripheral neuropathy, previous amputation, renal insufficiency, or a history of walking barefoot.
Most DFIs are polymicrobial, with aerobic gram-positive cocci (GPC), especially staphylococci, being the most common causative organisms. In countries with warm climates, gram-negative bacilli (especially Pseudomonas aeruginosa) are more prevalent. Recent studies of complicated skin and soft tissue infections in developed countries have shown less than 10% isolation of P. aeruginosa. The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in DFIs has ranged from 5% to 30% in recent studies.
Diabetic foot osteomyelitis (DFO) may be present in up to 20% of mild to moderate and 50%-60% of severely infected wounds. DFO should be considered in ulcers that are deep, large, chronic, or over a bony prominence. Noninfectious neuroarthropathy (Charcot foot) is sometimes difficult to distinguish from DFO and can coexist. Plain radiographic changes of osteomyelitis (cortical erosion, periosteal reaction, mixed lucency, and sclerosis) may lag clinical disease by up to a month, and diagnosis may require the use of serial radiographs or magnetic resonance imaging (MRI).
A prolonged course of antibiotics (3-6 months) has a clinical success rate of 65%-80% in DFO. The choice between surgical and nonsurgical treatment has to be made on an individualized basis.
Implementation
Clinicians should consider infection in any foot wound in a diabetic patient. Evaluation should be done at 3 levels: the patient as a whole, the affected foot, and the infected wound. The affected limb should be assessed for arterial ischemia, venous insufficiency, presence of protective sensation, and biomechanical problems. Hospitalization should be considered for severe infection, moderate infection with complication (peripheral arterial disease or lack of home support), or failure to improve on outpatient therapy.
For mild infection not recently treated with antibiotics, routine cultures are not routinely required. For all other infections, a specimen should be obtained from deep tissue (by biopsy or curettage) after the wound has been cleaned and debrided.
Any wound that has necrotic tissue or surrounding callus should be debrided. While topical antimicrobials may be used for mild infections, they should not be used in noninfected wounds, because they can interfere with wound healing and promote bacterial resistance. Wounds also must be properly dressed and off-loaded of pressure, and patients need regular follow-up.
Empiric antibiotic therapy can be narrowly targeted at aerobic GPC in many acutely infected patients; but those at risk for infection with antibiotic-resistant organisms or with chronic, previously treated, or severe infections usually require broader-spectrum regimens. Coverage for P. aeruginosa is needed only in selected patients (frequent soaking of feet, failure of nonpseudomonal therapy, or severe infection). Empiric therapy against MRSA should be considered in patients with a prior history of MRSA infection, high local prevalence of MRSA, and severe infections. Parenteral therapy should be initiated in severe infections.
Antibiotics should not be continued beyond resolution of clinical signs of infection, usually 1-2 weeks for mild infections and 2-3 weeks for moderate to severe infections.
All patients should have a plain radiograph of the affected foot to look for bony abnormalities, soft-tissue gas, and radio-opaque foreign bodies. MRI is more sensitive and specific and is useful if a soft-tissue abscess is suspected or if the diagnosis of DFO is uncertain. If MRI is contraindicated, a combined radionuclide bone scan and a labeled white blood cell scan should be considered for the diagnosis of DFO.
The most definitive way to diagnose DFO is by bone culture and histology. Treatment requires prolonged use of antibiotics and/or surgical treatment.
Most DFIs require some surgical intervention, ranging from minor (debridement) to major (resection, amputation). Urgent surgical intervention is needed in the presence of deep tissue gas, abscess, and necrotizing fasciitis. Revascularization should be considered early in the presence of ischemia.