Diabetic foot infection

Background

• Foot infection in a patient with diabetes mellitus, typically superimposed infection of a preexisting diabetic foot ulcer

Microbiology

• Typically polymicrobial, including:
  • Staphylococcus aureus, which is by far the most common cause of monomicrobial infections
  • Coagulase-negative staphylococci
  • Streptococcus
  • Enterococcus
  • Enterobacteriaceae
  • Pseudomonas aeruginosa
  • Anaerobes, including Bacteroides fragilis
• Anaerobes are more likely to be involved in deeper, more chronic ulcers

Classification

IDSA/IWGDF

Clinical Manifestation	Severity	PEDIS Grade
Wound lacking purulence or any manifestations of inflammation	Uninfected	1
Presence of ≥ 2 manifestations of inflammation (purulence, or erythema, tenderness, warmth, or induration), but any cellulitis/erythema extends ≤ 2cm around the ulcer, and infection is limited to the skin or superficial subcutaneous tissues; no other local complications or systemic illness	Mild	2
Infection (as above) in a patient who is systemically well and metabolically stable but which has ≥ 1 of the following characteristics: cellulitis extending >2cm, lymphangitic streaking, spread beneath the superficial fascia, deep-tissue abscess, gangrene, and involvement of muscle, tendon, joint or bone	Moderate	3
Infection in a patient with systemic toxicity or metabolic instability (e.g. fever, chills, tachycardia, hypotension, confusion, vomiting, leukocytosis, acidosis, severe hyperglycemia, or azotaemia)	Severe	4

WIfI System

• The WIfI system is used to stage at-risk limbs in patients with peripheral artery disease, including those with diabetes
• Components include Wound, Ischemia, and foot Infection
• Clinical stage from 0 (very low) to 3 (high) which predicts amputation risk

Diagnosis

• Osteomyelitis should be considered in all cases of diabetic foot infection
  • Probe-to-bone test should be done routinely
  • Plain film X-ray can be helpful, though not sensitive
  • MRI is the preferred diagnostic test, followed by bone and white cell scan
  • The gold standard is still bone biopsy for histopathology and culture

Management

Severity	Common Pathogens	Antibiotics	Notes
Mild	methicillin-susceptible Staphylococcus aureus, Streptococcus	dicloxacillin	qid dosing and very narrow-spectrum
		clindamycin	active against MRSA but higher risk of CDAD
		cephalexin	qid dosing
		levofloxacin	not as effective against Staphylococcus aureus
		amoxicillin-clavulanic acid	broad-spectrum, includes anaerobic coverage
	methicillin-resistant Staphylococcus aureus	doxycycline	uncertain activity against streptococci
		TMP-SMX	uncertain activity against streptococci
moderate or severe	MSSA, Streptococcus, Enterobacteriaceae, anaerobes	levofloxacin	suboptimal against MSSA
		cefoxitin
		ceftriaxone
		ampicillin-sulbactam
		moxifloxacin
		ertapenem
		tigecycline
		fluoroquinolone with clindamycin
		imipenem-cilastatin
	MRSA	linezolid
		daptomycin
		vancomycin
	Pseudomonas aeruginosa	piperacillin-tazobactam

Duration

Site of Infection	Severity	Duration
soft tissue only	mild	1 to 2 weeks; up to 4 weeks if slow-to-resolve
	moderate	1 to 3 weeks
	severe	2 to 4 weeks
bone and joint infection	postamputation, with no residual infection	2 to 5 days
	postamputation, with residual soft tissue infection	1 to 3 weeks
	postamputation, with residual bone infection	4 to 6 weeks
	no surgery	≥3 months

• Osteomyelitis
  • Traditionally, 6 weeks of parenteral therapy
  • May be able to shorten to 3 weeks if adequately debrided, based on more recent evidence1

Further Reading

• The Neuropathic Diabetic Foot Ulcer Microbiome IsAssociated With Clinical Factors. Diabetes. 2013;62:923-930.