Diabetic Foot Infection (Antimicrobial)

A diagnosis of diabetic foot infection MUST be made using clinical signs and symptoms, not just microbiological results. All open wounds will be colonised with organisms, making the positive culture difficult to interpret.
Key recommendations:

Only use antibiotics if clinical signs of infection
Send microbiological samples early in infection – tissue aspirates are preferable to wound swabs
Continue therapy until the infection has resolved, not until the wound has healed
Treatment plan should include wound care, pressure relief and early vascular assessment, with referral to vascular surgeons if impalpable foot pulses – see Wound formulary
Osteomyelitis
- suspect if able to touch bone through the wound with a sterile probe
- suspect in a non-healing diabetic ulcer with adequate blood supply
- refer to Combined Diabetic Foot Clinic
- deep swab or tissue samples are essential for diagnosis. Delay therapy pending microbiology results in chronic cases
- treat for 6 weeks minimum.
Typical pathogens (antibiotic-naïve = no systemic antimicrobials in last 3 months)
- antibiotic-naïve: Staph aureus and beta-haemolytic streptococci
- not antibiotic-naïve or chronic: as above plus Gram-negative bacilli, enterococci, anaerobes.
Discuss treatment options with Microbiology if organisms isolated are not covered by empiric guidance for severity of infection.
All doses are for adults with normal renal function or mild renal impairment.

Clinical manifestation of a diabetic foot infection	Infection severity	PEDIS grade
Wound lacking purulence or any manifestations of inflammation	Uninfected	1
Presence of ≥2 manifestations of inflammation (purulence, or erythema, pain, 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 (eg fever, chills, tachycardia, hypotension, confusion, vomiting, leukocytosis, acidosis, severe hyperglycaemia or azotaemia).	Severe	4

Table taken from: IDSA grading of severity of diabetic foot infection - see Lipsky, B. A. et al., 2004. Diagnosis and Treatment of Diabetic Foot Infections. Clinical Infectious Diseases, 39, pp. 885-910
NOTE: Definitions of terms can be found in footnotes to table 4 of the above reference.
Foot ischaemia may increase the severity of any infection, and the presence of critical ischaemia often makes the infection severe. PEDIS: perfusion, extent/size, depth/tissue loss, infection, and sensation.

For glossary of terms see Glossary.