Surgical Wound Classification System
The CDC surgical wound classification categorizes operative wounds into four classes (I-IV) based on the degree of contamination. This classification predicts surgical site infection risk and guides antibiotic prophylaxis decisions.
About
The CDC surgical wound classification was originally developed in 1964 and updated in 1985 by the CDC National Nosocomial Infections Surveillance (NNIS) system. Class I (Clean): Uninfected wound without inflammation, no entry into respiratory/alimentary/genital/urinary tract. Class II (Clean-Contaminated): Entry into controlled respiratory, alimentary, genital, or urinary tract without unusual contamination. Class III (Contaminated): Open wound with gross contamination, major break in sterile technique, or acute non-purulent inflammation. Class IV (Dirty/Infected): Existing clinical infection or perforated viscera. The classification correlates with surgical site infection (SSI) rates: Class I: 1-5%, Class II: 3-10%, Class III: 10-25%, Class IV: 25-40%.
Formula
Class I: Clean. Class II: Clean-Contaminated. Class III: Contaminated. Class IV: Dirty/Infected.
Class I Clean: No infection, no entry into viscus. Class II Clean-Contaminated: Controlled entry into respiratory, GI, GU tract. Class III Contaminated: Open wound, gross spillage, break in technique. Class IV Dirty: Established infection, perforated viscus.
Score Interpretation
Surgical site infections (SSIs) occur in 2-5% of all surgeries in the US, affecting 160,000-300,000 patients annually. Proper wound classification guides appropriate antibiotic prophylaxis and helps predict SSI risk. The NNIS risk index combines wound class, ASA score, and operative duration for more precise risk prediction.
Class I — Clean — 1–1
Infection rate: 1-5%.
Management: Prophylactic antibiotics generally not indicated without patient risk factors.
Class II — Clean-Contaminated — 2–2
Infection rate: 3-10%.
Management: Antibiotic prophylaxis indicated (single dose pre-operative).
Class III — Contaminated — 3–3
Infection rate: 10-25%.
Management: Extended prophylactic or therapeutic antibiotics. Consider wound irrigation.
Class IV — Dirty/Infected — 4+
Infection rate: 25-40%.
Management: Therapeutic antibiotics. Consider delayed primary closure. Wound culture.
Reference Ranges
| Population | Normal Range |
|---|---|
| All surgical wounds | Class I (Clean) to Class IV (Dirty/Infected) |
Tabeeb+ Medical Review Team
Expert surgical review panel.
View medical review board & editorial policy →Example Calculation
A clean thyroidectomy: Class I. Elective laparoscopic cholecystectomy: Class II. Open colon surgery with fecal spillage: Class III. Laparotomy for perforated diverticulitis with purulent peritonitis: Class IV.
Common Mistakes
Classifying all abdominal surgeries as Class III.
Class II is appropriate for elective GI surgery without gross spillage. Only significant contamination or spillage upgrades to Class III.
Frequently Asked Questions
Does wound class change for reoperation?
References
- CDC National Healthcare Safety Network. Surgical Site Infection Event. 2024.