Surgical wound classification is a foundational element of perioperative care that directly influences the management of postoperative infections and wound complications. Originally established in 1964 and refined by the Centers for Disease Control and Prevention (CDC), the surgical wound classification system remains a critical guide for clinicians to evaluate infection risk and standardize care protocols across surgical settings.¹ Proper evaluation and implementation of surgical wound classifications can also help wound care professionals to understand the perioperative circumstances surrounding a surgical wound or surgical site infection. 

What is Surgical Wound Classification?

The CDC classifies surgical wounds into 4 categories based on the degree of microbial contamination: Clean (Class I), Clean-Contaminated (Class II), Contaminated (Class III), and Dirty-Infected (Class IV). This classification assists surgical teams in identifying the potential for postoperative infections and tailoring prophylactic and therapeutic strategies accordingly¹:

• Class I – Clean: These are uninfected operative wounds that do not show signs of inflammation. They may utilize a closed drain system if a drain is required. These types of surgical wounds result from procedures with no entry into respiratory, alimentary, genital, or urinary tracts.
• Class II – Clean-Contaminated: This signifies operative wounds that may have a low level of contamination, possibly due to necessity of controlled entry into the respiratory, alimentary, genital, or urinary tracts.
• Class III – Contaminated: This type of surgical wound is considered contaminated, and many times is due to breaks in sterile technique or spillage from the GI tract. Incision sites with acute or nonpurulent inflammation may also trigger health care providers to consider classification as Class III, pending exact circumstances.
• Class IV – Dirty-Infected: These surgical wounds are potentially known to be dirty or infected prior to initial incision (for instance, debridement of an open wound with known osteomyelitis or abscess). One will typically note purulence or clear signs of infection or tissue devitalization in these cases. Perforated viscera can also contribute to classification as Dirty-Infected. 

Refinements and Relevance in Modern Perioperative Practice

The CDC’s refinement of this classification system includes more explicit definitions and criteria to ensure consistency across facilities.¹ They emphasize objective factors such as the presence of inflammation, the degree of sterile technique breach, and the nature of any microbial contamination encountered during the procedure. This more uniform approach is particularly valuable in operating rooms, where real-time decisions must be made to strive to reduce the likelihood of surgical site infections (SSIs).

A 2018 update on the definition of nosocomial infections emphasized that consistent and accurate classification not only improves communication among surgical staff but also impacts infection control metrics and hospital quality reporting. Misclassification, on the other hand, can lead to underreporting of SSIs and suboptimal use of antibiotic prophylaxis.²

Stratifying Postoperative Risk

Accurate surgical wound classification plays a pivotal role in risk stratification. For instance, the risk of SSI in a clean wound is typically less than 2%, whereas it can exceed 20% in dirty-infected wounds if appropriate preventive measures are not implemented.¹ This system helps healthcare professionals decide when prophylactic antibiotics are warranted, how to monitor wound healing, and what documentation is required to support quality assurance processes.

Additionally, by integrating wound classification into electronic health records and clinical decision-making tools, institutions can better track outcomes and identify areas for improvement in perioperative care.² As institutions collect data on SSIs and other complications, they can use this to inform organizational policy and best practices, as well. 

Conclusion

Surgical wound classification remains a cornerstone of safe and effective perioperative management. With the CDC’s refined definitions,¹ clinicians can more precisely assess infection risk, apply evidence-based interventions, and reduce the burden of SSIs. Emphasizing education and documentation around this system for the entire care team can help promote better patient outcomes and promotes better regulatory compliance in the surgical setting.

References

1. Herman TF, Popowicz P, Bordoni B. Wound Classification. [Updated 2023 Aug 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554456/
2. Onyekwelu I, Yakkanti R, Protzer L, Pinkston CM, Tucker C, Seligson D. Surgical Wound Classification and Surgical Site Infections in the Orthopaedic Patient. J Am Acad Orthop Surg Glob Res Rev. 2017 Jun 13;1(3):e022. doi: 10.5435/JAAOSGlobal-D-17-00022. PMID: 30211353; PMCID: PMC6132296.