Diabetic foot infections
Hyperglycemia, sensory and autonomic neuropathy, and peripheral arterial disease all contribute to the pathogenesis of lower extremity infections in diabetic patients. These infections are associated with substantial morbidity and mortality.
●Evaluation of a patient with a diabetic foot infection involves determining the extent and severity of infection through clinical and radiographic assessment, identifying and addressing underlying factors that predispose to and promote infection, assessing the microbial etiology, and determining the need for surgical intervention.
●Laboratory testing should include blood work to evaluate for leukocytosis as well as blood glucose, electrolytes, and renal function values so that glycemic control and acid base status can be evaluated and monitored. Baseline and subsequent inflammatory markers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) can be useful for monitoring response to therapy. Conventional radiographs should be done to evaluate for bony and soft tissue deformity or abnormalities. Formal vascular evaluation is warranted in cases where peripheral arterial insufficiency is suspected.
●The presence of two or more features of inflammation (erythema, warmth, tenderness, swelling, induration, or purulent secretions) can establish the diagnosis of a diabetic foot infection. The definitive diagnosis of osteomyelitis is made through histologic and microbiologic evaluation of a bone biopsy sample. However, certain clinical factors can support the presumptive diagnosis of osteomyelitis in the absence of biopsy:
•Grossly visible bone or ability to probe to bone
•Ulcer size larger than 2 cm2
•Ulcer duration longer than one to two weeks
•Erythrocyte sedimentation rate (ESR) >70 mm/h
Those with one or more of the above factors whose radiographs are normal or indeterminate for osteomyelitis should undergo magnetic resonance imaging (MRI).
●Management of diabetic foot infections requires attentive wound management, good nutrition, antimicrobial therapy, glycemic control, and fluid and electrolyte balance. Wound management includes attentive local wound care including debridement of callus and necrotic tissue, wound cleansing, and relief of pressure on the ulcer. Consultation with a surgeon with experience in diabetic foot infection is important for cases of severe infections and most cases of moderate infections. Prompt surgical debridement is critical for cure of infections complicated by abscess, extensive bone or joint involvement, crepitus, necrosis, gangrene or necrotizing fasciitis and is important for source control in patients with severe sepsis.
The microbiology of diabetic foot wounds varies with the severity and extent of involvement． Superficial infections are likely due to aerobic gram-positive cocci whereas deep, chronically infected, and/or previously treated ulcers are more likely to be polymicrobial. Anaerobic organisms may also be involved in wounds with extensive local inflammation, necrosis, or gangrene. When there is concern for multidrug-resistant organisms or in cases of moderate or severe infection (including deep infections and osteomyelitis), aerobic and anaerobic cultures of deep tissue or bone biopsies should be obtained at the time of debridement. Organisms cultured from superficial swabs are not reliable for predicting the pathogens responsible for deeper infection.
●Empiric antibiotic therapy should be selected based upon the severity of infection and the likelihood of involvement of resistant organisms:
•For patients with mild infections, we suggest an empiric antimicrobial regimen with activity against skin flora including streptococci and Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus [MRSA] if risk factors are present) (Grade 2C).
•For patients with deep ulcers, we suggest an empiric antimicrobial regimen with activity against streptococci, staphylococci (and MRSA if risk factors are present), aerobic gram-negative bacilli and anaerobes (Grade 2C). Oral antibiotics may be appropriate for ulcers that extend to the fascia, whereas parenteral regimens should be used for deeper infections.
•For patients with limb-threatening diabetic foot infections or evidence of systemic toxicity, we suggest treatment with a broad-spectrum parenteral antibiotic regimen with activity against streptococci, MRSA, aerobic gram-negative bacilli, and anaerobes (Grade 2C).
●Antimicrobial therapy should be tailored to culture and susceptibility results when available, and a switch to an oral from parenteral regimen is reasonable following clinical improvement. Antibiotics need not be administered for the entire duration that the wound remains open. Close follow-up is important to ensure continued improvement and to evaluate the need for modification of antimicrobial therapy, further imaging, or additional surgical intervention.
●Many patients with osteomyelitis of the foot benefit from surgical resection. However, in certain cases, limited surgical debridement combined with prolonged antibiotic therapy may be appropriate. The duration of antibiotic therapy of osteomyelitis depends on the extent of residual affected tissue.
If appropriate wound cultures were submitted, antimicrobial therapy should be tailored to culture and susceptibility results when available. However, it is not always necessary to cover all microorganisms isolated from cultures. Virulent species such as S. aureus and streptococci (group A or B) should always be covered, but in polymicrobial infections, less virulent organisms (such as coagulase negative staphylococci and enterococci) may be less important. Furthermore, if isolates are resistant to an empiric regimen to which the patient is clearly responding well, broadening the spectrum to include those isolates may not be necessary. On the other hand, if the patient is not responding, expanding therapy to target all isolated organisms may be warranted.
For those patients who were initiated on parenteral therapy, a switch to an oral regimen is reasonable following clinical improvement.
Duration of therapy
The duration of antibiotic therapy should be tailored to individual clinical circumstances. Patients with mild infection should receive oral antibiotic therapy in conjunction with attentive wound care until there is evidence that the infection has resolved (usually about one to two weeks). Antibiotics need not be administered for the entire duration that the wound remains open .
Patients with infection also requiring surgical debridement should receive intravenous antibiotic therapy perioperatively. In the absence of osteomyelitis, antibiotic therapy should be administered in conjunction with attentive wound care until signs of infection appear to have resolved (two to four weeks of therapy is usually sufficient). If there is a good response to parenteral therapy, oral agents can be used to complete the course of treatment．
Patients requiring amputation of the involved limb should receive intravenous antibiotic therapy perioperatively. If the entire area of infection is fully resected, a brief course of oral antibiotic therapy (about a week) following surgery is usually sufficient .