This is the CodeSystem that contains all the codes in NHSN Surveillance System Codes (https://www.cdc.gov/nhsn/cdaportal/terminology/codesystem/cdcnhsn.html) and NHSN Surveillance System Codes (https://www.cdc.gov/nhsn/cdaportal/terminology/codesystem/cdcnhsn.html). E.g. what you have to deal with if you get resources containing codes in either of them