Table 2.

Levels of contamination (LOC) adapted from CDC and the corresponding SSI rates [6, 7]

LOC	Criteria	SSI rates
Class I/clean	- Uninfected operative wounds - No inflammation is encountered - The respiratory, alimentary, genital, or uninfected urinary tracts are not entered.	1–5%
Class II/clean-contaminated	- The respiratory, alimentary, genital, or urinary tracts are entered under controlled conditions and without unusual contamination. - No evidence of infection or major break in technique is encountered.	3–11%
Class III/contaminated	- Operations with major breaks in sterile technique or gross spillage from the gastrointestinal tract - Incisions in which acute, non-purulent inflammation is encountered - Outside object had contact with the wound (e.g. a bullet, knife blade).	10–17%
Class IV/dirty-infected	- Involve existing clinical infection - Perforated viscera - Foreign object lodged in the wound - Any wound that has been exposed to pus or faecal matter.	>27%