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

Wound

Grade	DFU	Gangrene	Description
0	No ulcer	No gangrene	Minor tissue loss. Salvageable with simple digital amputation or skin coverage.
1	Small, shallow ulcer on distal leg or foot; no exposed bone, unless limited to distal phalanx	No gangrene	Minor tissue loss. Salvageable with simple digital amputation or skin coverage
2	Deeper ulcer with exposed bone, joint, or tendon; generally not involving the heel; shallow heel ulcer, without calcaneal involvement	Gangrene limited to digits	Major tissue loss salvageable with multiple digital amputation or standard TMA ± skin coverage
3	Extensive deep ulcer involving forefoot and/or midfoot; deep full thickness heel ulcer ± calcaneal involvement	Extensive gangrene involving forefoot and/or midfoot; full thickness heel necrosis ± calcaneal involvement	Extensive tissue loss salveagable only with a complex foot reconstruction or non-traditional TMA (Chopart or Lisfranc); flap coverage or complex wound management needed for large soft tissue defect

Ischemia

Grade	ABI	Ankle SBP (mmHg)	Toe pressure, TcPO2 (mmHg)
0	≥0.8	>100	≥60
1	0.6-0.79	70-100	40-59
2	0.4-0.59	50-70	30-39
3	≤0.39	<50	<30

Foot Infection

Grade	Clinical Description
0	No signs or symptoms of infection.
1	Infection present with at least 2 of: local swelling or induration; erythema 0.5 to 2 cm around the ulcer; local tenderness or pain; local warmth; purulent discharge. Local infection involving only the skin and subcutanous tissue, without involvement of deeper tissues and without systemic signs. Excludes other causes of inflammation such as trauma, gout, acute Charcot foot, fracture, thrombosis, venous stasis.
2	Local infection (as above) with erythema >2 cm around ulcer or involving deeper structures (abscess, osteomyelitis, septic arthritis, fasciitis), without systemic signs of infection.
3	Local infection (as above) with systemic signs of infection (SIRS) with at least 2 of: temperature <36ºC or >38ºC; heart rate >90 bpm; respiratory rate >20 bpm or PaCO2 <32 mmHg; WBC <4 or >12 or 10% bands

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.