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Diabetic Foot Infection
MAZEN S. BADER, MD, MPH, Memorial University of Newfoundland School of Medicine, St. John’s, Newfoundland, Canada
Foot infections are common in patients with diabetes and are associated with high morbidity and risk of lower extrem-
ity amputation. Diabetic foot infections are classified as mild, moderate, or severe. Gram-positive bacteria, such as
Staphylococcus aureus and beta-hemolytic streptococci, are the most common pathogens in previously untreated
mild and moderate infection. Severe, chronic, or previously treated infections are often polymicrobial. The diag-
nosis of diabetic foot infection is based on the clinical signs and symptoms of local inflammation. Infected wounds
should be cultured after debridement. Tissue specimens obtained by scraping the base of the ulcer with a scalpel or
by wound or bone biopsy are strongly preferred to wound swabs. Imaging studies are indicated for suspected deep
soft tissue purulent collections or osteomyelitis. Optimal management requires aggressive surgical debridement and
wound management, effective antibiotic therapy, and correction of metabolic abnormalities (mainly hyperglycemia
and arterial insufficiency). Treatment with antibiotics is not required for noninfected ulcers. Mild soft tissue infection
can be treated effectively with oral antibiotics, including dicloxacillin, cephalexin, and clindamycin. Severe soft tissue
infection can be initially treated intravenously with ciprofloxacin plus clindamycin; piperacillin/tazobactam; or imi-
penem/cilastatin. The risk of methicillin-resistant S. aureus infection should be considered when choosing a regimen.
Antibiotic treatment should last from one to four weeks for soft tissue infection and six to 12 weeks for osteomyelitis
and should be followed by culture-guided definitive therapy. (Am Fam Physician. 2008;78(1):71-79, 81-82. Copyright
2008 American Academy of Family Physicians.)
T Patient informa-
tion: A handout on
diabetic foot infection,
written by the author of
this article, is provided on
page 81.
Inpatientswithdiabetes,anyfootinfec- blistering,orpenetratingforeignbody.Motor neuropathy can result in foot deformities (e.g., claw toe) that contribute to local pres- superficial paronychia to deep infection sure from footwear, making skin ulceration involving bone. Types of infection include even more likely. Once the skin is broken cellulitis, myositis, abscesses, necrotizing (typically on the plantar surface), the under- fasciitis, septic arthritis, tendinitis, and lying tissues are exposed to colonization by osteomyelitis. Foot infections are among the pathogenic organisms. The resulting wound infection may begin superficially, but with diabetes mellitus. They are associated with delay in treatment and impaired body defense increased frequency and length of hospital- ization and risk of lower extremity amputa- tion and vascular insufficiency, it can spread tion.1 Foot ulceration and infection are the to the contiguous subcutaneous tissues and to leading risk factors for amputation.2 Preven- tion and prompt diagnosis and treatment are necessary to prevent morbidity, especially begin with an ulcer, localized cellulitis and necrotizing fasciitis can develop in theabsence of an ulcer or traumatic injury.
Pathophysiology
Patients with diabetes are particularly sus- Microbiology
ceptible to foot infection primarily because of neuropathy, vascular insufficiency, and viously untreated, superficial infected foot diminished neutrophil function.3 Peripheral wounds in patients with diabetes are aerobic neuropathy has a central role in the devel- gram-positive bacteria, particularly Staphy- opment of a foot infection and it occurs in lococcus aureus and beta-hemolytic strepto- about 30 to 50 percent of patients with diabe- cocci (group A, B, and others).5 Infection tes. Patients with diabetes lose the protective in patients who have recently received anti- sensations for temperature and pain, impair- biotics or who have deep limb-threatening ing awareness of trauma such as abrasions, Downloaded from the American Family Physician Web site at www.aafp.org/afp. Copyright 2008 American Academy of Family Physicians. For the private, noncommercial use of one individual user of the Web site. All other rights reserved. Contact copyrights@aafp.org for copyright questions and/or permission requests.
Diabetic Foot Infection
SORT: KEY RECOMMENDATIONS FOR PRACTICE
The existence, severity, and extent of infection, as well as vascular status, neuropathy, and glycemic control should be assessed in patients with a diabetic foot infection.
Visible bone and palpable bone on probing are suggestive of underlying osteomyelitis in patients with Before an infected wound of a diabetic foot infection is cultured, any overlying necrotic debris should be removed to eliminate surface contamination and to provide more accurate results.
Routine wound swabs and cultures of material from sinus tracts are unreliable and strongly discouraged in the management of diabetic foot infection.
The empiric antibiotic regimen for diabetic foot infection should always include an agent active against Staphylococcus aureus, including methicillin-resistant S. aureus if necessary, and streptococci.
A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, see http://www.aafp.
org/afpsort.xml. caused by a mixture of aerobic gram-positive, aerobic It can clinically mimic cellulitis and presents as erythema, gram-negative (e.g., Escherichia coli, Proteus species, edema, and elevated temperature of the foot. Most patients Klebsiella species), and anaerobic organisms (e.g., Bacte- with diabetic foot infection do not have systemic features roides species, Clostridium species, Peptococcus and Pep- such as fever or chills. The presence of systemic signs or tostreptococcus species).5 Anaerobic bacteria are usually symptoms indicates a severe deep infection.12 part of mixed infections in patients with foot ischemiaor gangrene.6 Methicillin-resistant S. aureus (MRSA) is ESTABLISHING EXTENT OF INFECTION
a more common pathogen in patients who have been Early recognition of the area of involved tissue can facili- previously hospitalized or who have recently received tate appropriate management and prevent progression of antibiotic therapy. MRSA infection can also occur in the the infection (Figure 3). The wound should be cleansed absence of risk factors because of the increasing preva- and debrided carefully to remove foreign bodies or necrotic material and should be probed with a sterilemetal instrument to identify any sinus tracts, abscesses, Clinical Evaluation
Key elements for evaluating and treating diabetic foot Osteomyelitis is a common and serious complication of infection are summarized in Figure 1.9 diabetic foot infection that poses a diagnostic challenge.
A delay in diagnosis increases the risk of amputation.13 CONFIRMING THE DIAGNOSIS
Risk factors associated with osteomyelitis are summa- Diabetic foot infection must be diagnosed clinically rather rized in Table 1.3,13-16 Visible bone and palpable bone by than bacteriologically because all skin ulcers harbor micro- probing are suggestive of underlying osteomyelitis in organisms (Figure 2). The clinical diagnosis of foot infec- patients with a diabetic foot infection.13-14 Laboratory tion is based on the presence of purulent discharge from an studies, such as white blood cell count and the erythrocyte ulcer or the classic signs of inflammation (i.e., erythema, sedimentation rate (ESR), have limited sensitivity for the pain, tenderness, warmth, or induration). Other sugges- diagnosis of osteomyelitis. Osteomyelitis is unlikely with tive features of infection include foul odor, the presence normal ESR values; however, an ESR of more than 70 mm of necrosis, and failure of wound healing despite optimal per hour supports a clinical suspicion of osteomyelitis.13 management.10 Local inflammatory findings may be less Definitive diagnosis requires percutaneous or open bone prominent or absent in some diabetic foot infections. For biopsy. Bone biopsy is recommended if the diagnosis of example, pain and tenderness may be reduced or absent osteomyelitis remains in doubt after imaging.3 in patients who have neuropathy, whereas erythema maybe absent in those with vascular disease.11 Acute Char- ESTABLISHING SEVERITY OF INFECTION
cot’s foot is characterized by a progressive deterioration The severity of the infection determines the appropriate of weight-bearing joints, usually in the foot or ankle.
antibiotic regimen and route of administration. It also is 72 American Family Physician
Volume 78, Number 1 V July 1, 2008 Evaluation and Treatment of Diabetic Foot Infection
Assess neurologic and vascular status of foot Reassess in two to four days (earlier, if dramatically worsens) therapy, granulocyte colony-stimulating factor, etc.
Figure 1. Algorithm for the evaluation and treatment of diabetic foot infection.
Adapted with permission from Lipsky BA. Medical treatment of diabetic foot infections. Clin Infect Dis. 2004;(39 suppl 2):S110. July 1, 2008 V Volume 78, Number 1 American Family Physician 73
Diabetic Foot Infection
Figure 2. A noninfected ulcer of the dorsum of the foot in
Figure 3. Plantar foot ulcers with a deep space infection.
a patient with previous amputation of the toes.
Venous insufficiency can be diagnosed clinically by the primary consideration in determining the need for the presence of edema and skin changes and confirmed hospitalization and the indications and timing for any surgical intervention. A practical and simple approach toclassifying diabetic foot infection is provided in Table 2.3 ASSESSING NEUROPATHY
Touch, vibration, and pressure sensations should be OBTAINING CULTURES
checked routinely using cotton wool, tuning fork, and Before an infected wound is cultured, any overlying 10-g nylon monofilament, respectively.
necrotic debris should be removed by scrubbing thewound with saline-moistened sterile gauze to eliminate Diagnostic Imaging
surface contamination.3,17 For wound culture, tissue Diagnostic imaging is not necessary for every patient specimens should be obtained by scraping the base of with diabetes who has a foot infection. Plain radiography the ulcer with a scalpel or curette, or by a biopsy of the of the foot is indicated for detection of osteomyelitis, for- wound or bone. Needle aspiration of the pus or tissue eign bodies, or soft tissue gas. Bony abnormalities asso- fluid performed aseptically is an acceptable alternative ciated with osteomyelitis may be indistinguishable from method. Cultures of wound swabs or material from sinus the destructive effects of Charcot’s foot and are usu- tracts are unreliable and are strongly discouraged.17-19 ally not evident on plain radiography until two to four The specimen should be processed for a Gram-stained weeks after initial infection.21 When plain radiography is smear and aerobic and anaerobic cultures.
negative but osteomyelitis is clinically suspected, radio-nuclide scan or magnetic resonance imaging should be ASSESSING VASCULAR STATUS
performed (Table 321-23). Combining technetium bone Peripheral artery disease (PAD) can be diagnosed byabsence of foot pulses and reduced ankle-brachial index(ABI). Calculation of ABI is done by measuring the rest- Table 1. Risk Factors for Osteomyelitis
ing systolic blood pressure in the ankle and arm using in Patients with Diabetic Foot Infection
a Doppler probe. An ABI of 0.91 to 1.30 is borderline ornormal. An ABI of 0.41 to 0.90 indicates mild to moder- Appearance of a swollen, deformed red toe (also called ate PAD and an ABI of 0.40 or less indicates advanced ischemia. An ABI greater than 1.30 suggests the presence of calcified vessels and the need for additional vascular Infected ulcer with an erythrocyte sedimentation rate studies, such as pulse volume recording or measure- ment of the toe-brachial index. Patients with atypical Nonhealing ulcer after a few weeks of appropriate care and symptoms, or whose diagnosis is in doubt, should have Radiologically evident bone destruction beneath ulcer ABI measured after exercise on a treadmill. An ABI that Ulcer area greater than 2 cm2 or more than 3 mm deep decreases by 20 percent following exercise is diagnostic Ulceration presents over bony prominences for more than of PAD, whereas a normal ABI following exercise rules out PAD. If a PAD diagnosis is confirmed and revascu- Ulceration with unexplained leukocytosis larization is planned, magnetic resonance angiography,computed tomography angiography, or contrast angiog- Information from references 3 and 13 through 16. raphy can be performed for anatomic evaluation.20 74 American Family Physician
Volume 78, Number 1 V July 1, 2008 Diabetic Foot Infection
Table 2. Clinical Classification of Diabetic Foot Infection
Clinical manifestations of infection Wound lacking purulence or any manifestations of inflammation (i.e., erythema, pain, tenderness, warmth, Presence of purulence and/or two or more manifestations of inflammation, but any cellulitis or erythema extends 2 cm or less around the ulcer; infection is limited to the skin or superficial subcutaneous tissues; no other local complications or systemic illness Infection (purulence and/or two or more manifestations of inflammation) in a patient who is systemically well and metabolically stable, but who has at least one of the following characteristics: cellulitis extending more than 2 cm around the ulcer; lymphangitic streaking; spread beneath the superficial fascia; deep tissue abscess; gangrene; involvement of muscle, tendon, joint, or bone Infection (purulence and/or two or more manifestations of inflammation) in a patient with systemic toxicity or metabolic instability (e.g., fever, chills, tachycardia, hypotension, confusion, vomiting, leukocytosis, acidosis, severe hyperglycemia, azotemia) Adapted from Lipsky BA, Berendt A, Deery G, et al., for the Infectious Diseases Society of America. Diagnosis and treatment of diabetic foot infec-tions. Clin Infect Dis. 2004;39(7):894. Table 3. Diagnostic Imaging Studies for Osteomyelitis of the Foot in Patients with Diabetes
Lateral, anteroposterior, and oblique views should be done initially in all patients with diabetes who are suspected to have a deep infection Because 30 to 50 percent of the bone must be destroyed before lytic lesions appear, plain radiography should be repeated at two-week intervals if initial findings are not normal, but the infection fails to resolve Soft tissue swelling and subperiosteal elevation are the earliest findings of Useful in between soft tissue and bone infection and for determining the Should be considered for patients with diabetes who have an infection with no bone exposed, who have been treated for two to three weeks with modest clinical improvement, and who have negative or inconclusive results on plain radiography High sensitivity for osteomyelitis and can differentiate it from cellulitis Abnormal findings for osteomyelitis (which typically become evident within 24 to 48 hours after onset of symptoms) include increased flow activity, blood pool activity, and positive uptake on three-hour images Specificity for osteomyelitis is decreased in patients with diabetes who have Charcot’s foot or recent trauma or surgery; further imaging is usually required Sensitivity and specificity are increased when combined with technetium The main advantage is the marked improvement in specificity when Should not be used as part of regular osteomyelitis imaging Superior to magnetic resonance imaging for detecting sequestra Information from references 21 through 23. July 1, 2008 V Volume 78, Number 1 American Family Physician 75
Diabetic Foot Infection
scan with gallium scan or white blood cell scan may for more extensive amputation.32 Emergent surgery is improve the diagnostic yield for osteomyelitis.21,22 Mag- required for severe infection in an ischemic limb, necro- netic resonance imaging provides more accurate infor- tizing fasciitis, gas gangrene, and an infection associated mation regarding the extent of the infectious process.23 with compartment syndrome. Surgical excision of affected Ultrasonography and computed tomography are also bone has historically been the standard of care in patients helpful in evaluating abnormalities in the soft tissue with osteomyelitis. Nevertheless, successful therapy with (e.g., abscess, sinus tract, cortical bone involvement) and a long course of antibiotics alone has been achieved in two may provide guidance for diagnostic and therapeutic thirds of patients with osteomyelitis.12 As infection is con- aspiration, drainage, or tissue biopsy.21 trolled and the wound starts to granulate, primary closuremay be successful. The wound may also be treated surgi- Treatment
cally with a flap or graft, left to heal by secondary inten- Effective management of diabetic foot infection requires tion, or managed with negative pressure dressings.33 If the infected limb appears to be ischemic, the patient debridement and resection of dead tissue, appropriate should be referred to a vascular surgeon. Although non- wound care, and correction of metabolic abnormalities.
critical ischemia can usually be treated without a vascu-lar procedure, early revascularization within a few days ANTIBIOTIC THERAPY
of the infection is required for successful treatment of an The selection of antibiotic therapy for diabetic foot infection involves decisions about choice of empiricand definitive antibiotic agent, route of administration,and duration of treatment (Tables 43,9 and 53,24-30). Initial Table 4. Principles of Antibiotic Therapy
empiric antibiotic therapy should be based on the sever- for Diabetic Foot Infection
ity of the infection, history of recent antibiotic treatment,previous infection with resistant organisms, recent cul- Empiric antibiotic regimen should include an agent active ture results, current Gram stain findings, and patient against Staphylococcus aureus, including methicillin-resistant factors (e.g., drug allergy). A Gram-stained smear of an S. aureus if necessary, and streptococci appropriate wound specimen may help guide therapy.
Coverage for aerobic gram-negative pathogens is required for The overall sensitivity of a Gram-stained smear for iden- severe infection, chronic infection, or infection that fails to tifying organisms that grow on culture is 70 percent.9 The empiric antibiotic regimen for diabetic foot infection Necrotic, gangrenous, or foul-smelling wounds usually require should always include an agent active against S. aureus, Initial empiric antibiotic therapy should be modified on the basis including MRSA if necessary, and streptococci.3,5,7,8 of the clinical response and culture or susceptibility testing The patient should be reassessed 24 to 72 hours after Virulent organisms, such as S. aureus and streptococci, should initiating empiric antibiotic therapy to evaluate the always be covered in polymicrobial infection response and to modify the antibiotic regimen, if indi- Coverage for less virulent organisms, such as coagulase-negative cated by early culture results. Several antibiotics have been shown to be effective, but no single regimen has Parenteral antibiotics are indicated for patients who are shown superiority.3,24-30 Antibiotic therapy should not be systemically ill, have severe infection, are unable to tolerate oral agents, or have infection caused by pathogens that are used for foot ulcers without signs of infection because it does not enhance wound healing or prevent infec- Using oral antibiotics for mild to moderate infection and tion.31 Clinical failure of appropriate antibiotic therapy switching early from parenteral to oral antibiotics with might be because of patient nonadherence, antibiotic appropriate spectrum coverage and good bioavailability and resistance, superinfection, undiagnosed deep abscess or osteomyelitis, or severe tissue ischemia.
Although topical antibiotics can be effective for the treatment of mildly infected ulcers, they should not be routinely used SURGICAL TREATMENT
Discontinuation of antibiotics should be considered when all signs and symptoms of infection have resolved, even if the Surgery is the cornerstone of treatment for deep diabetic foot infection. Procedures range from simple incision and Cost should be considered when selecting antibiotic therapy drainage to extensive multiple surgical debridements andamputation. Timely and aggressive surgical debridement Information from references 3 and 9. or limited resection or amputation may reduce the need 76 American Family Physician
Volume 78, Number 1 V July 1, 2008 Diabetic Foot Infection
Table 5. Empiric Antibiotic Regimens for Treatment of Diabetic Foot Infection
Soft tissue infection
Dicloxacillin 500 mg orally four times per day Cephalexin (Keflex) 500 mg orally four times per day For penicillin-allergic patients, except those with immediate hypersensitivity reactions Amoxicillin/clavulanate (Augmentin) 875/125 mg orally Clindamycin (Cleocin) 300 to 450 mg orally three times Potential cross-resistance and emergence of resistance in erythromycin-resistant Staphylococcus aureus; inducible resistance in MRSA Doxycycline (Vibramycin) 100 mg orally twice per day Sulfamethoxazole/trimethoprim (Bactrim) 160/800 mg is two to four weeks, depending on response; administer orally or parenterally followed by orally) Ampicillin/sulbactam (Unasyn) 3 g IV four times per day Ceftriaxone (Rocephin) 1 to 2 g IV once per day plus clindamycin 600 to 900 mg IV or orally three times per day or metronidazole (Flagyl) 500 mg IV or orally three times per day Levofloxacin (Levaquin) 500 mg IV or orally once per day plus clindamycin 600 to 900 mg IV or orally three times per day Moxifloxacin (Avelox) 400 mg IV or orally once per day Ciprofloxacin (Cipro) 400 mg IV twice per day plus clindamycin 600 to 900 mg IV three times per day Piperacillin/tazobactam (Zosyn) 3.375 to 4.500 g IV Imipenem/cilastatin (Primaxin) 500 mg IV four times Vancomycin 30 mg per kg IV twice per day plus Vancomycin is the parenteral drug of choice ciprofloxacin 400 mg IV twice per day plus metronidazole 500 mg IV or orally three times per day or orally twice per day or daptomycin (Cubicin) 4 mg per kg IV once per day can also be used for MRSA Use vancomycin for penicillin-allergic patients Tigecycline (Tygacil) 100 mg IV loading dose then Bone or joint infection
Use the above parenteral or oral antibiotic regimens Use the above parenteral or oral antibiotic regimens Initially use the above parenteral antibiotics followed by oral antibiotics for four to six weeks Initially use the above parenteral antibiotics followed by oral antibiotics for eight to 12 weeks IV = intravenously; MRSA = methicillin-resistant Staphylococcus aureus; MSSA = methicillin-susceptible S. aureus. *—Risk factors for polymicrobial infection include chronic ulcers, recent antibiotic use, and foot ischemia or gangrene. Information from references 3 and 24 through 30. Diabetic Foot Infection
WOUND MANAGEMENT
Figures 2 and 3 courtesy of David G. Armstrong, MD.
The wound should be dressed to allow for careful inspec-tion for evidence of healing and early identification of The Author
new necrotic tissue. Necrotic or unhealthy tissue should MAZEN S. BADER, MD, MPH, is an assistant professor of medicine at the be debrided, preferably surgically or with topical debrid- Memorial University of Newfoundland School of Medicine in St. John’s, ing agents. Removing pressure from the foot wound is Canada. He received his medical degree from Istanbul (Turkey) University School of Medicine and his master of public health degree from the Uni- crucial for healing35 and can be achieved through total versity of Kansas in Lawrence. Dr. Bader completed an internal medicine contact casting, removable cast walkers, and various residency at the University of Chicago (Ill.) Pritzker School of Medicine ambulatory braces, splints, modified half-shoes, and and an infectious diseases fellowship at the University of Kansas Medical Center in Kansas City. sandals.36 Edema of the legs can delay wound healing;controlling edema with leg elevation, compression stock- Address correspondence to Mazen S. Bader, MD, MPH, 300 Prince Phil-lip Dr., Division of Infectious Diseases, St. John’s, NL, Canada A1B3V6 ings, or a pneumatic pedal compression device enhances (e-mail: msbader1@hotmail.com). Reprints are not available from the the healing process.37 Evidence of resolution of infec- tion includes formation of granulation tissue, absence of Author disclosure: Nothing to disclose.
necrotic tissue, and closing of the wound. If osteomyeli-tis is present, signs of healing include a drop in ESR and REFERENCES
loss of increased uptake on nuclear scan.
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METABOLIC STABILITY
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