There is no standard, clinically agreed upon definition for purulence.  For NHSN surveillance purposes, the descriptors “pus” or “purulence” are sufficient gross anatomic evidence of infection.  When the terms ‘pus’ or ‘purulence’ are not written in the medical record, NHSN has allowed determinations for purulence based off descriptors. Documentation that uses a color descriptor and a consistency descriptor (from the list below) in combination is acceptable to indicate ‘purulence’.  For example, fluid only described as yellow, or only described as thick, is not sufficient. However, if the terms are combined, then they may be more representative of purulence (for example: fluid described as thick and yellow). Color Green Yellow Consistency Milky Thick Creamy Opaque Viscous   NOTE: The following descriptors cannot be used to define purulence/infection: ‘Cloudy’, ‘turbid’, ‘murky’ or the odor of a wound. Gram stain results such as WBCs or PMNs cannot be used to define purulence within the SSI protocol [PDF – 1 MB].