Earlier quoted context omitted.
Honestly, I would be okay with someone being tried for murder over this shit. Isn't the death penalty supposed to be a deterrence?
It's very clearly not murder; that'd set really bad precedents. You might be able to pull off something like involuntary manslaughter, but I tend to doubt it.
Two possible problems:
1) It might hurt tracing efforts if people are worried about being prosecuted (ie. people "clam up"). For example, this particular story might not be known at all. Hurting tracing harms public health, so this might be a good enough reason not to go after irresponsible people on the basis of tracing infections at all.
2) I'm not aware of the law ever holding anyone responsible for non-deliberate infection. New legal ground would have to be broken in this area.