What is the most likely cause of a surgical site infection in a patient with a history of surgery, presenting with pain, redness, swelling, and greenish discharge on their hand?

Staphylococcus aureus is the Most Likely Causative Organism

The answer is A. Staphylococcus aureus is the most common pathogen causing surgical site infections, particularly in clean hand procedures, and should be the primary target of empirical therapy. 1, 2

Why Staphylococcus aureus is the Answer

• S. aureus is identified as the key pathogen in SSIs, particularly following clean surgical procedures on the hand, making it the most likely organism in this clinical scenario 1, 2
• The presence of pain, redness, swelling, and purulent discharge within 30 days of surgery meets diagnostic criteria for a superficial incisional SSI, where S. aureus predominates 3, 4
• While the greenish discharge might suggest Pseudomonas aeruginosa to some clinicians, S. aureus remains statistically the most common SSI pathogen overall and should be considered first-line in clean hand surgery 1, 2

Why the Other Options Are Less Likely

Pseudomonas aeruginosa (Option D)

• While Pseudomonas can produce greenish discharge and should be considered in contaminated or traumatic wounds, it is not the most common SSI pathogen in clean surgical procedures 1
• Pseudomonas coverage becomes important in contaminated/traumatic hand wounds with mixed flora, but the question describes a previous surgical scar, suggesting a clean procedure 1

Streptococcus pyogenes (Option B)

• Streptococcus species are secondary pathogens in hand SSIs but occur less frequently than S. aureus 1
• Streptococcal infections typically present with rapidly spreading cellulitis rather than localized purulent discharge 3

Clostridium perfringens (Option C)

• Clostridial infections are associated with contaminated wounds, gas gangrene, and necrotizing infections with crepitus and rapid tissue destruction 4
• This organism is not a common cause of routine SSIs and would present with more dramatic findings including severe pain out of proportion to examination, crepitus, and systemic toxicity 4

Clinical Implications for Management

• First-line empirical antibiotic therapy for clean hand procedures should target methicillin-susceptible S. aureus (MSSA) with agents like cephalexin, cefazolin, or dicloxacillin 1
• In regions with high MRSA prevalence, consider vancomycin, daptomycin, or linezolid pending culture results 3
• The primary treatment remains surgical: open the wound, evacuate infected material, and perform irrigation, with antibiotics reserved for patients showing systemic signs (fever ≥38.5°C, tachycardia ≥100 bpm, or cellulitis >5 cm) 1, 4

Critical Pitfall to Avoid

• Do not let the greenish discharge color alone drive you toward Pseudomonas as the answer—epidemiologic data consistently shows S. aureus as the most common SSI pathogen, and empirical coverage should reflect this statistical reality 1, 2
• Always obtain Gram stain and culture before initiating antibiotics to confirm the pathogen and adjust therapy accordingly 1