By the power of truth, I, while living, have conquered the universe.
Posted by: orphan
This is correct. Take the Ark Portal on Earth, and the artifact on Reach. I wouldn't be surprised of Flood were not present on The Ark before High Charity arrived.
lolwut?
"But it doesn't know about the portal - where it leads." ~ Cortana, Floodgate
The Gravemind is connected to all other Flood forms, there can't have been any Flood on the Ark otherwise he'd know where to go. Also, the Ark was designed as a haven outside the galaxy, the one place the Flood never managed to reach.
There was potential for the Flood to be shoehorned into Reach, I had a theory a long while back that sort of made sense of it with Reach being an artificial planet and all. But clearly there weren't any.