You know, given what little Caleb has described in the intro stuff he's shown us, there are two things that stand out to me.
1) Although he talks about breakdown of higher brain functions, there's nothing there that prevents Casualties from having basically a form of long-term Alzheimers where their cognition increases randomly as Twitch makes random neurons still alive in the dying parts of the brain fire. I'd imagine a lot of people got caught solely because they treated Casualties as unthinking or unable to plan in short bursts.
2) Vectors may start losing higher brain functions immediately, but I could easily see someone who was infected and starting to Vector using their weapons they died with, since they'd have enough higher brain function to remember that killing things makes them edible.
In a different tack, there's nothing to prevent Latents from living on Casualty meat.