This is the CodeSystem that contains all the codes in NHSN Occasion Of Detection (http://terminology.hl7.org/CodeSystem/NHSNOccasionOfDetection) and NHSN Occasion Of Detection (http://terminology.hl7.org/CodeSystem/NHSNOccasionOfDetection). E.g. what you have to deal with if you get resources containing codes in either of them