I saw that! Yikes! The TV show doesn't follow the comics all that closely, but massive hordes of zombies from time to time are a big part of it. Hope they all get away!
OK, so on the Talking Dead they said that Patrick’s illness was modeled after the 1918 flu pandemic. So that means that we can expect to see mostly people in the young adult to middle age getting the virus.
In the first scene of the first episode of this season, we saw one of the Walkers who had died from the flu at the fence. Rick noticed him while he was wearing his ear buds.
And Karen and “David” who both showed flu symptoms and were isolated in A block, had both been killing Walkers at the fence towards the beginning of the episode.
I almost fell off my chair when I saw the size of that herd!