54612 is a radio ID, not a talkgroup. The general idea behind the system has changed over the years. It is no longer the "state police system", it is a shared system with countless local, regional, state, and federal resources operating on it. I am not part of the health district, but health districts do not operate in a vacuum. Mass immunizations, health scares, and health screenings regularly require coordination between multiple health districts. Why build a separate radio system for these agencies when there is a perfect system already built? The DESPP system has superior coverage in the areas that the regional health districts operate in and building a talkgroup is virtually free. As to why they need to do a roll call, that's an operational policy respective to the agencies. I would imagine that it is for a couple of reasons. The familiarity of the radios and system, identification of any coverage gaps, and testing of one of the health district's primary notification systems. Why are tone tests performed, SMS text tests performed, or storm siren tests done? So that operators know how to use the equipment, they can ensure that it is in working order, and build muscle memory as to how they are to respond. Much of this is fact and some are inference, hope it answered your questions.