OPU - Unsolicited Population/Location-Based Laboratory Observation Message (Event R25 )

This message structure represents the way most submissions to veterinary laboratories occur. There is a multi-tier hierarchy in which a single individual (for example, a veterinarian or an owner of a production facility) submits one or more specimen samples from one or more animals or non-living entity, such as environmental specimens or feed. This grouped submission of specimens from multiple animal 'patients' is usually referred to as an 'accession' which can be considered analogous to a 'visit' in the veterinary laboratory context. This is what accounts for the unusual structure where the PV1 segment precedes a repeatable PID segment.