Definition: A factor, such as a microorganism, chemical substance, or form of radiation, whose presence, excessive presence, or (in deficiency diseases) relative absence is essential, in whole or in part, for the occurrence of a condition.
\nConstraint: The use of this participation is limited to observations.
\nhttp://terminology.hl7.org/CodeSystem/v3-ParticipationType
where concept is-a CAGNT