Surgical site infections (SSIs) are generally classified based on the depth of the infection and the anatomical location involved. The National Healthcare Safety Network (NHSN) classifies surgical wounds into four categories which, while related to infection risk, are used to assess the likelihood of infection. Based on these classifications, while they don't define the types of infections, they inform the risk of different kinds of infections occurring. These classifications are relevant to understanding SSI risk profiles:
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Clean (C): These wounds are created under sterile conditions, do not involve entering the respiratory, alimentary, or genitourinary tracts, and have a low risk of infection (around 1-5%). An example is an elective hernia repair.
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Clean-Contaminated (CC): These wounds involve entering the respiratory, alimentary, or genitourinary tracts under controlled conditions, without significant spillage. Infection risk is slightly higher than clean wounds (around 3-10%). An example is elective bowel resection.
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Contaminated (CO): These wounds involve a major break in sterile technique, gross spillage from the gastrointestinal tract, or fresh traumatic wounds. Infection risk is notably higher (around 10-17%). An example is a colon resection with significant spillage.
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Dirty/Infected (D): These wounds involve pre-existing infection, devitalized tissue, or foreign bodies. They have the highest risk of infection (around 25-40%). An example includes an incision and drainage of an abscess.
It's important to note that while these classifications are crucial for risk assessment and prevention strategies, they are wound classifications and not classifications of the different types of infections themselves. A surgical site infection, regardless of the wound classification, can manifest as superficial incisional, deep incisional, or organ/space infection.
