A 58-year-old man undergoes elective open cholecystectomy. On postoperative day 5, he develops fever (38.5°C), erythema, and purulent discharge from the surgical incision. Which investigation is most appropriate to confirm the diagnosis and guide antimicrobial therapy?

Question

Accepted Answer

A. Wound swab for culture and sensitivity. ## Investigation of Choice for Surgical Site Infection

### Clinical Context
The patient presents with classic signs of surgical site infection (SSI) on postoperative day 5: fever, incision erythema, and purulent drainage. The diagnosis is clinically apparent, but microbiological confirmation and antibiotic susceptibility are essential for targeted therapy.

### Why Wound Swab Culture & Sensitivity is Correct

**Key Point:** Wound swab for culture and sensitivity is the gold standard investigation for SSI because it:
- Directly samples the infected site
- Identifies the causative organism
- Provides antibiotic susceptibility data for targeted therapy
- Guides de-escalation from empiric broad-spectrum antibiotics

**High-Yield:** SSI microbiology varies by surgery type:
- Clean surgery (cholecystectomy): *Staphylococcus aureus*, *Streptococcus pyogenes*, *E. coli*
- Clean-contaminated (biliary, GI): Gram-negatives + anaerobes
- Contaminated/dirty: Polymicrobial

### Proper Technique for Wound Swab
1. Cleanse surrounding skin with antiseptic
2. Swab purulent material from the wound depth (not superficial skin)
3. Use sterile swab; place in appropriate transport medium
4. Send for aerobic AND anaerobic culture (SSI can be polymicrobial)

**Clinical Pearl:** Superficial skin flora contamination is common; deep wound swabs are more representative of true infection.

### Timing and Interpretation
- Culture results typically available in 48–72 hours
- Interim empiric therapy (e.g., cefazolin or cephalosporin for clean surgery SSI) should be started immediately
- De-escalate once susceptibilities are known

**Mnemonic:** **SWAB = Site-specific, Wound-depth, Aerobic + anaerobic, Broad-spectrum initial therapy**

Answer

B. Procalcitonin level

Answer

C. Complete blood count with differential

Answer

D. Blood culture and sensitivity

A 58-year-old man undergoes elective open cholecystectomy. On postoperative day 5, he develops fever (38.5°C), erythema, and purulent discharge from the surgical incision. Which investigation is most appropriate to confirm the diagnosis and guide antimicrobial therapy?

Explanation

Investigation of Choice for Surgical Site Infection

Clinical Context

Why Wound Swab Culture & Sensitivity is Correct

Proper Technique for Wound Swab

Timing and Interpretation

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