Diagnosing Infected Skin Ulcers

Primary Diagnostic Criteria

A skin ulcer is considered infected when there is purulent discharge or at least two cardinal signs of inflammation, including erythema, warmth, swelling/induration, and pain/tenderness, as recommended by the Infectious Diseases Society of America 1, 2
The presence of purulent discharge alone is diagnostic of an infected skin ulcer, according to the Infectious Diseases Society of America 1, 2
Erythema extending >0.5 cm from the wound margin is a sign of infection, as suggested by the Diabetes/Metabolism Research and Reviews 2
Warmth around the ulcer is a sign of infection, as indicated by the Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews 1, 2
Swelling or induration of surrounding tissue is a sign of infection, as recommended by the Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews 1, 2
Pain or tenderness is a sign of infection, although it may be blunted in neuropathic patients, as noted by the Clinical Infectious Diseases, Diabetes/Metabolism Research and Reviews 1, 2, 3

The presence of necrotic tissue in the wound is a secondary suggestive feature of infection, as suggested by the Diabetes/Metabolism Research and Reviews 2
Friable or discolored granulation tissue is a secondary suggestive feature of infection, as indicated by the Diabetes/Metabolism Research and Reviews and Clinical Infectious Diseases 2, 4
Foul odor from the wound is a secondary suggestive feature of infection, as noted by the Diabetes/Metabolism Research and Reviews and Clinical Infectious Diseases 2, 4
Non-purulent secretions that are excessive are a secondary suggestive feature of infection, as suggested by the Diabetes/Metabolism Research and Reviews 2
Failure to heal despite appropriate wound care is a secondary suggestive feature of infection, as indicated by the Diabetes/Metabolism Research and Reviews and Clinical Infectious Diseases 2, 4

Mild infection is characterized by cellulitis/erythema extending <2 cm from wound margin, limited to skin or superficial subcutaneous tissue, and no systemic signs present, as defined by the Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews 2, 5
Moderate infection is characterized by cellulitis extending ≥2 cm from wound margin or involvement of deeper structures, with the patient remaining systemically stable, as defined by the Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews 2, 5
Severe infection is characterized by systemic toxicity, including fever >38°C or <36°C, tachycardia >90 bpm, tachypnea >20/min, leukocytosis >12,000/mm³ or leukopenia <4,000/mm³, as defined by the Clinical Infectious Diseases 5, 6, 2

For pressure ulcers, the Infectious Diseases Society of America suggests infection when there is purulent discharge plus four of the following signs: fever, worsening mental or functional status, warmth, redness, swelling, localized tenderness/pain, or serous drainage, as recommended by the Clinical Infectious Diseases 7, 8

The Infectious Diseases Society of America recommends against relying on surface swab cultures to diagnose infection, as all ulcers are colonized and surface cultures cannot differentiate colonization from true infection 1, 7, 8
The Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews suggest that high bacterial counts do not necessarily equal infection, and quantitative microbiology should not be used to diagnose infection without clinical signs 2, 4
The Clinical Infectious Diseases and Diabetes/Metabolism Research and Reviews note that neuropathy and ischemia can mask typical signs of infection, and systemic symptoms like fever may be absent in 50% of limb-threatening infections 3, 5, 6

The Infectious Diseases Society of America recommends obtaining cultures for moderate-to-severe infections to guide antibiotic therapy, as indicated by the Clinical Infectious Diseases 1, 5
Deep tissue specimens, rather than superficial swabs, should be obtained for culture, as recommended by the Clinical Infectious Diseases 1, 5
Blood cultures are indicated for severe infections with systemic illness, as suggested by the Clinical Infectious Diseases 1, 5