Purulent Skin & Soft-Tissue Infection (Abscess)

SSTI

Patient + scenario modifiers

Patient

Clinical scenario / source

Annotations only — chart still shows the full chemistry of each drug.

1. Clinical Syndrome

Skin & soft-tissue infection with purulent drainage or fluctuance — abscess, furuncle, carbuncle. Distinguished from non-purulent cellulitis (no fluctuance, no drainage), which is usually β-hemolytic strep.

2. Pathogens

Consider the patient: MRSA risk factors (prior MRSA, IV drug use, recent hospitalization, household contact), immunocompromise, diabetes (neuropathy → unrecognized wounds).

Consider the case: Severity (mild = abscess only; moderate = abscess + systemic signs; severe = sepsis or rapid progression). I&D is the cornerstone of treatment for any drainable collection.

Common

- Staphylococcus aureus (MSSA)
  Most purulent SSTI is S. aureus.
- Staphylococcus aureus (MRSA)
  ~30% of community S. aureus SSTI is MRSA in many US regions.

Less common

- Streptococcus pyogenes (Group A Strep)
  More common in non-purulent / cellulitis.

3. Empiric Therapy

Tier	First choice	Alternatives	Duration	Comments
Outpatient	Incision & drainage — · primary therapy · topical · — I&D is the primary therapy for drainable abscess. Antibiotics added for size / immunocompromise / cellulitis / systemic signs.	—	5–7 days if antibiotics added	Mild: I&D alone if <2 cm, no surrounding cellulitis, immunocompetent host.
Outpatient — with comorbidities	100 mg · PO BID · PO · 5–7 days	TMP-SMX DS 1–2 tabs (160/800 mg) · PO BID · PO · 5–7 days 300–450 mg · PO QID · PO · 5–7 days Higher C. diff risk — reserve. Inducible MRSA resistance — request D-test.	5–7 days	Moderate disease: I&D + oral abx active against MRSA. Empiric MRSA coverage is standard for purulent SSTI.
Admitted to ward	15–20 mg/kg · q8–12h · IV · 7–14 days (clinical response)	600 mg · q12h · IV · 7–14 days 4 mg/kg · q24h · IV · 7–14 days	7–14 days clinical-response	Severe disease, systemic signs, failed outpatient therapy, or unable to tolerate PO.

4. Directed Therapy

Wound culture (after I&D) usually identifies S. aureus. Tailor to MSSA (cefazolin / cephalexin PO) or MRSA (continue current). Stop antibiotics if cultures negative + clinical resolution after I&D.

5. Monitoring

Resolution: wound size decreasing, decreasing erythema, afebrile. Most abscesses don't need further imaging. Recurrent abscesses → decolonization (mupirocin nares + chlorhexidine wash) + screen for IVDU / household reservoir.

Toxicity: TMP-SMX K+ + Cr; doxy photosensitivity counseling; linezolid CBC if >2 weeks.

Pearls

I&D is curative for most abscesses ≤2 cm — antibiotics are the adjunct, not the primary therapy. USEEK criteria for adding abx: Unable to drain, Systemic signs, Extremes of age, Extensive cellulitis, Kompromised host (immune).