But for the sake of argument there is, as far as we know, only one Flood Infection Form on the ship. Remember that they quarantined the ship multiple times and when Serina said "something has happened", she doesn't appear to be suffering from rampancy, and Rampancy was an already established issue by the release of Halo Wars. This means that the order to abandon ship was made very early in the Spirit's (as of right now) 26 year journey home. And, if the Flood had assimilated the crew after exiting the Cryotubes, wouldn't there be Flood Biomass or blood on the floor and walls of said room? And wouldn't there be Flood Biomass on the hull, like every other Flood controlled vessel? I think that the crew abandoned ship for a completely different reason than the Flood, and that they never knew about its presence on the Spirit of Fire when they left. I also believe that, given the fiery exit of the Sheild World, that the parasite must have been either inside the the ship by the time of leaving, which isn't possible given that the Spirit of Fire wouldn't have been allowed to open the exit if Flood were present on the ship (even though the planet was collapsing), since that is a primary mechanic of that last mission. And even if an Infection form had managed to latch on to the hull as they were flying through the exit, it would have been either crushed/pulled by the gravitational forces the supernova was exhibiting moments before it's collapse, and the proximity to the star the Spirit experiences would have certainly killed anything on or within the outer hull. Which is why I believe that the parasite boarded the ship [i]after[/i] the crew abandoned ship, though the why the ship would still be flying without the crew or Serina is odd. Also, certainly the Covenant have the coordinates to the Apex Site, so finding the Spirit of Fire wouldn't have been that hard given the current state of affairs and it's obvious trajectory.