Surgical Site Infection

Surgical site infections (SSI) result from microbial contamination of the surgical wound, most commonly from the patient's own skin or mucosal flora. The risk is determined by the interaction of three factors: microbial contamination dose, virulence of the organism, and host resistance. Wounds are classified by contamination level: Class I (Clean—2% SSI risk), Class II (Clean-Contaminated—10% risk, GI/GU/respiratory tract entered under controlled conditions), Class III (Contaminated—20% risk, open traumatic wound, gross spillage from GI tract), and Class IV (Dirty-Infected—40% risk, existing infection or perforated viscus). SSI classification includes superficial incisional (skin and subcutaneous tissue), deep incisional (fascia and muscle), and organ/space (any anatomic area opened during surgery). Staphylococcus aureus (including MRSA) is the most common SSI pathogen in clean surgeries, while polymicrobial infections with enteric gram-negatives and anaerobes dominate in contaminated procedures. Biofilm formation on surgical implants (prosthetic joints, mesh) creates persistent infection resistant to antibiotic therapy. The SSI prevention bundle addresses modifiable risk factors: glucose control reduces neutrophil dysfunction; normothermia maintains perfusion and immune function; appropriate antibiotic prophylaxis achieves tissue drug levels before contamination occurs.