ADT/ACK - Merge person - patient ID (for backward compatibility only)

An A39 event is used to signal a merge of records for a person that was incorrectly filed under two different PID-2 - Patient IDs. The _incorrect source patient ID_ identified in the MRG segment (MRG-4 - Prior Patient ID) is to be merged with the required _correct target patient ID_ identified in the PID segment (PID-2 - Patient ID). The _incorrect source patient ID_ would then logically never be referenced in future transactions. It is noted that some systems may still physically keep this _incorrect identifier_ for audit trail purposes or other reasons associated with database index implementation requirements.