Class I/Clean	An uninfected operative wound where there is no inflammation; the respiratory, alimentary, genital, or uninfected urinary tract is not entered. In addition, clean wounds are primarily closed and, if necessary, drained with closed drainage. Operative incisional wounds that follow no penetrating (blunt) trauma should be included in this class, whether it meets the criteria or not.
Class II/Clean-Contaminated	An operative wound in which the respiratory, alimentary, genital, or urinary systems are under controlled conditions and without unusual contamination. Specifically, in this category, biliary tract, vagina, appendix, and oropharynx surgery can be included, provided no evidence of infection or major break in a sterile technique is encountered.
Class III/Contaminated	This is the class that considers wounds contaminated. Fresh, open wounds, which may result from an insult to sterile techniques or leakage from the gastrointestinal tract into the wound, belong to this class. In addition, incisions that result in acute purulent inflammation or without pus are to be considered Class 3 wounds.
Class IV/Dirty-Infected	Wounds considered absolutely infected. These are typically traumatic wounds that have been treated incorrectly and in an inappropriate manner. They are characterized by devitalized tissue and are most commonly caused by microorganisms present in perforated viscera or in the surgical field.