Skin and soft tissue infections are among the commonest reasons for an antibiotic prescription, and most of the decisions are made on examination rather than investigation. This review sets out where the evidence sits.
The first split is purulent versus non-purulent, because it predicts the organism: non-purulent infection is usually beta-haemolytic streptococcal, purulent infection usually Staphylococcus aureus. Cellulitis presents with warmth, pain, tenderness, erythema and oedema; an abscess with a fluctuant tender area. Laboratory testing is of limited use in most patients — a statement worth taking literally, since inflammatory markers are routinely sent and rarely change anything. Where the examination cannot distinguish cellulitis from abscess, point-of-care ultrasound can.
Treatment follows the split. Non-purulent infection gets an antibiotic with streptococcal cover — penicillin V, dicloxacillin or a cephalosporin. An abscess gets incision and drainage, with antibiotics added only in selected patients rather than routinely. Elevate the limb; non-steroidal anti-inflammatories may help pain and inflammation. Decolonisation for recurrent disease remains contested. Most patients can be discharged with follow-up; sepsis, immunosuppression, failed outpatient treatment or an inability to adhere to therapy are the reasons to escalate. Newer agents — tedizolid, delafloxacin, omadacycline, ceftaroline — are for selected cases, not for routine cellulitis.
- Classify purulent versus non-purulent first; it determines the organism and the antibiotic
- Do not send inflammatory markers expecting them to change management
- Use point-of-care ultrasound when you cannot tell cellulitis from abscess
- Drain the abscess; antibiotics are an addition for selected patients, not the treatment
- Escalate for sepsis, immunosuppression, adherence problems or outpatient failure — not for size alone
Why it matters
Most of the investigation performed for cellulitis does not alter the antibiotic, and the decision it should alter is whether there is pus.
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