Key Points
- Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
- Use system-specific risk tools to guide testing and disposition.
- Order high-yield tests first; escalate imaging when indicated.
- Start evidence-based initial therapy and reassess frequently.
Algorithm
- Primary survey and vitals; IV access and monitors.
- Focused history/physical; identify red flags and likely etiologies.
- Order system-appropriate labs and imaging (see Investigations).
- Initiate guideline-based empiric therapy (see Pharmacology).
- Reassess response; arrange consultation and definitive management.
Clinical Synopsis & Reasoning
Differentiate non‑purulent cellulitis from purulent abscess and necrotizing infections. Examine for systemic toxicity, immunosuppression, and anatomic traps (hand, perineum). Point‑of‑care ultrasound distinguishes abscess requiring drainage from phlegmon and can guide procedural planning.
Treatment Strategy & Disposition
Incise and drain purulent collections when present; choose empiric antibiotics based on local MRSA prevalence, host factors, and severity. Outline margins to assess response and elevate affected limb; arrange close follow‑up for diabetics and immunocompromised. Admit for systemic toxicity, rapid progression, or failure of oral therapy; involve surgery when necrotizing fasciitis is suspected.
Epidemiology / Risk Factors
- Immunosuppression, devices; recent hospitalization
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|---|---|---|
| CBC | Inflammation/infection | Leukocytosis/leukopenia | |
| Lactate | Hypoperfusion | Elevated | Trend |
| Blood cultures | Pathogen ID | Positive/negative | Before antibiotics if feasible |
When to Add MRSA Coverage
| Situation | Examples |
|---|---|
| Purulent infection | Pus, draining lesions, carbuncles |
| Failed beta-lactam therapy | Worsening after 48–72 h |
| High risk | Prior MRSA, IVDU, crowding, recent hospitalization |
Pharmacology
| Medication | Mechanism | Onset | Role in Therapy | Limitations |
|---|---|---|---|---|
| Cephalexin/cefazolin | β-lactam | Hours | MSSA/streptococcal coverage | Allergy |
| TMP-SMX or doxycycline | Folate antagonism / 30S | Hours | CA-MRSA coverage | Hyperkalemia / photosensitivity |
| Clindamycin | 50S inhibition | Hours | Toxin suppression (Group A strep) | C. difficile risk |
| Piperacillin-tazobactam | Broad β-lactam | Hours | Severe/nec fasc mixed coverage | AKI |
Prognosis / Complications
- Depends on host and source control; sepsis/organ failure risk
Patient Education / Counseling
- Explain red flags and when to seek emergent care.
- Reinforce medication adherence and follow-up plan.
Notes
Consider special organisms with exposures (Eikenella in human bites, Vibrio in seawater). Necrotizing infection red flags: pain out of proportion, bullae, crepitus, rapid progression.