If you haven't been Patient Zero in a while, well now ya are!
noarchive server variable to track the round number (increments on GAMEEVENT_LEVEL_INIT)
noarchive server variables for all players (is set whenever player becomes PZ, is a random number on initial join of 1 to 3 rounds before the round counter)
When choosing PZ, pick the person who has the highest difference between current round, and the last round they were PZ.
If you haven't been Patient Zero in a while, well now ya are!
GAMEEVENT_LEVEL_INIT)