An evidence-based approach to diabetic foot infections
Section snippets
Pathophysiology
Although not all foot infections are the result of bacterial invasion of ulcerations, this sequence of events is a common pathway leading to serious diabetic lower extremity sepsis. Predisposing factors for limb-threatening lower extremity infection are similar to those for ulceration and include neuropathy, macrovascular and microvascular impairments, as well as decreased resistance to infection, which is often referred to as immunopathy [19], [20], [21].
Loss of protective sensation resulting
Microbiology
Polymicrobial involvement is the rule in severe diabetic foot infections, whereas mild infections are often monomicrobial. Gram-positive cocci predominate in most infections, but gram-negative rods and anaerobic organisms are also frequently isolated from deeper or limb-threatening infections [7], [21], [35], [36], [37], [38], [39], [40]. In the latter circumstances, 3 to 5 organisms can often be cultured. As indicated, the most common organisms cultured are the aerobic gram-positive cocci. The
Clinical presentation (classification)
Foot infection in diabetic patients is most frequently a sequela to neuropathic or neuroischemic foot ulceration [6], [7], [12], [20], [38]. The open lesion allows entry of microbes that flourish in the presence of an impaired host response [1], [38], [53]. In patients with vascular insufficiency, the infection rapidly progresses and can quickly evolve into a limb- or life-threatening situation. Because of the neuropathic patients' loss of protective sensation, the emergent nature of an
Management
The severity of the infection, medical status of the patient, and history of medication allergies will usually guide antibiotic therapy [6], [7], [38], [55]. Initial antimicrobial treatment of diabetic foot infections therefore requires careful consideration of these factors in concert with an understanding of antibiotic spectrums of activity, toxicities, and interactions. Once definitive reliable cultures are reported, initial antibiotic regimens should be revised to narrow the coverage to
Treatment of non–limb-threatening infections
These relatively mild infections are often associated with superficial ulcers and can usually be managed without hospitalization. Persons with underlying critical ischemia or deep infection should not be considered in this category. Most non–limb-threatening infections are primarily monomicrobial, with aerobic gram-positive cocci, such as S aureus, Staphylococcus epidermidis, and streptococci (including enterococci) predominating [39], [63], [67], [68]. Nevertheless, gram-negative organisms can
Treatment of limb-threatening infections
Severe, limb-threatening infections include those with ≥2 cm of cellulitis, lymphangitis, deep ulceration or abscess, necrosis, gangrene, osteomyelitis, or critical ischemia [35], [53], [66], [67]. These patients require immediate hospitalization for surgical drainage, metabolic control, and parenteral antibiotic therapy [12], [19], [66], [73]. Fever or systemic signs of infection, including leukocytosis, may not be present in up to 50% of cases because of diabetes-related immunosuppression [12]
Management of osteomyelitis
Osteomyelitis is frequently associated with moderate to severe diabetic foot infections and complicates management [12], [37], [84], [85], [107]. In a series of 2,000 foot infections, Calhoun and Mader [107] noted that osteomyelitis was the most common clinical presentation. In a report of an antibiotic clinical trial for diabetic foot infections, 59 of 96 patients (61%) had underlying osteomyelitis [37]. An earlier study by Newman et al [89] found that osteomyelitis was present in 68% of the
Summary
Management of diabetic foot infections requires a thorough knowledge of the multiple factors involved, including the relevant microbiological characteristics of these infections. Equally important, the practitioner must maintain a current understanding of appropriate diagnostic and treatment protocols. Because no one specific antibiotic regimen will always be appropriate, management of the infected diabetic foot usually requires a combination of therapies. Typically, these include a variety of
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