A 52-year-old man undergoes elective colorectal surgery for adenocarcinoma. On postoperative day 5, he develops fever (38.5°C), erythema, and purulent discharge from the surgical wound. Which investigation is most appropriate to confirm the diagnosis and guide antimicrobial therapy?

Explanation

## Investigation of Choice for Surgical Site Infection **Key Point:** Wound swab for culture and sensitivity is the gold standard investigation for confirming bacterial SSI and identifying the causative organism, enabling targeted antimicrobial therapy. ### Why Culture & Sensitivity? Wound swab culture provides: - **Organism identification** — essential for targeted antibiotic selection - **Sensitivity pattern** — determines which antibiotics are effective - **Epidemiological data** — tracks nosocomial pathogens and resistance trends - **Direct evidence** — confirms bacterial infection rather than inflammatory response ### Technique for Optimal Yield 1. Obtain swab from **purulent material or wound exudate** (not surrounding skin) 2. Use sterile swab and transport medium 3. Avoid antiseptics immediately before sampling 4. Send promptly to microbiology lab **Clinical Pearl:** In SSI with purulent discharge, culture is mandatory before starting empiric antibiotics; however, if systemic toxicity is present, empiric broad-spectrum coverage should not be delayed pending results. ### Common SSI Pathogens | Organism | Frequency | Typical Context | | --- | --- | --- | | *Staphylococcus aureus* (MSSA/MRSA) | 20–30% | Most common; skin flora | | *Escherichia coli* | 15–20% | GI surgery | | *Pseudomonas aeruginosa* | 10–15% | Moist wounds, immunocompromised | | *Enterococcus* spp. | 5–10% | Polymicrobial, biliary/GI | | *Clostridium difficile* | Rare | Antibiotic-associated | **High-Yield:** SSI is classified as superficial (skin/subcutaneous), deep (fascia/muscle), or organ-space; culture guides therapy regardless of depth. [cite:Sabiston Textbook of Surgery 21e Ch 12]