RE - "Patient county is a required field in the V2 specification, in US Core Patient, Patient.address.district (county) is not specifically called out. Is it worth creating a new profile for this IG that is based on US Core, in order to require county?" 

If the idea is that this information could support individual case investigation and classification, and knowing that patient address as well as any other patient contact or demographic info, may be tough to get, and knowing that PH must get some detail to guide jurisdiction assignment for triaging and workflow, it might be helpful to include a county profile so we can still get some indication of location without full address. At a minimum state or territory would be needed for initial routing. County would be ideal. We can derive county off of address, but only if we get it.