Microbiology, Infection Control and Sepsis
Sterilisation and disinfection
Sterilisation destroys all organisms including spores: steam autoclave at 121 °C for 15 minutes at 15 psi, or 134 °C for 3 minutes; dry heat at 160 °C for 2 hours; ethylene oxide for heat-sensitive equipment; gamma irradiation for single-use items. The Spaulding classification separates critical items (entering sterile tissue - must be sterilised), semicritical (mucous membrane - high-level disinfection) and non-critical (skin contact - low-level disinfection).
Surgical site infection
Wounds are classified clean, clean-contaminated, contaminated and dirty; infection rates rise accordingly. Chlorhexidine-alcohol is superior to povidone-iodine for skin preparation. Prophylactic antibiotics are given within 60 minutes of incision (120 minutes for vancomycin and fluoroquinolones), redosed for long operations or major blood loss, and stopped within 24 hours - prophylaxis treats no existing infection. SSI is superficial incisional, deep incisional or organ/space; surveillance lasts 30 days, or 90 days with an implant.
Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response, quantified as a SOFA rise of 2 or more. Septic shock is vasopressor-dependent hypotension with MAP ≥65 mmHg and lactate >2 mmol/L despite adequate fluid. qSOFA (respiratory rate ≥22, altered mentation, systolic pressure ≤100) flags risk but does not diagnose. Manage with cultures before antibiotics, early broad-spectrum agents, source control and 30 mL/kg crystalloid for sepsis-induced hypoperfusion.
Rule of thumb: bacteraemia is not synonymous with sepsis - most septic patients are not bacteraemic, and positive cultures alone do not make the diagnosis.