If I amplify, it will happen in one of two ways: If I die, or if I spontaneously amplify. I could also in theory be triggered by live virus, but Kellis-Amberlee doesn't exist yet, so no other sources. There's some correlation between spontaneous amplification and bodily stress, but not enough to predict anything. At my size, I'll have about an hour and a half before I start snacking on everyone. I'll tell people if that happens, but you can also test me by having me read a random pattern, or asking me an involved question.
You shoot me in the head from a safe enough distance my blood doesn't splatter, and preferably we do it somewhere that's easy enough to burn everything in contact with my blood, and sterilize it. Then you burn my body, of course. It's actually the fairly standard zombie trope, really. Except that fresh zombies can move quickly. Humans will still outrun them, but I won't be shambling unless you let me stick around a couple months, which is ill advised.