In context of https://jira.hl7.org/browse/FHIR-28375 we propose that the Reference list be limited to US Core Practitioner Profile and all other base standard choices be optional.

The USCDI definition only states that Care Team members are "person(s) who participate or are expected to participate in the care team". Consequently, Organization should be optional rather than Must Support as other resources listed in the base standard.  We also suggest to not include Patient as Must Support. In many systems, Patient is solely the subject of the care and not documented as a participant with a particular role, thus the data source system would not have the ability need to document the patient as part of the care team in a particular role.

As the FHIR US Core profile is used for accessing and exchanging data based on what the source system has, this should not require the data source system to add functionality to capture a patient as part of the care team in a particular role beyond the subject.  Additionally, C-CDA does not impose this requirement either.

Links to pages:

http://hl7.org/fhir/us/core/STU3.1/StructureDefinition-us-core-careteam.html

https://build.fhir.org/ig/HL7/US-Core-R4/StructureDefinition-us-core-careteam.html