Working from LogicaHealth IG

https://covid-19-ig.logicahealth.org/StructureDefinition-COVID-19-underlying-medical-condition-presesnt.html

26 May discussion on extensibility see http://hl7.org/fhir/R4/extensibility.html#isModifier

See analysis spreadsheet by Linda Bird

FHIR elementBindingComments
Condition.codeCOVID19 General Comorbidity Value Set


Condition.modifierExtension:certaintyOfPresence

CertaintyOfPresenceVS