Effect Measure on the question of swine flu's "kill rate"

I'm guessing most everyone interested in swine flu already reads Effect Measure (as well you should; it was an invaluable resource in my reporting for my Slate piece on the mystery of the virulence of the outbreak in Mexico). But in case you haven't or are not, today's primer there on case fatality rates, virulence, and mortality would make an excellent start.

One of the things we'd like to know about the swine flu virus is its Case Fatality Ratio (CFR, commonly called a case fatality rate, although it isn't technically a rate but a proportion). But what is a CFR? And how is it different from a mortality rate?

The CFR is an estimate of the probability that someone with the swine flu will die of it (technically, before dying from something else or recovering). The higher the CFR, the more virulent the virus. So what's virulence? Virulence refers to the severity of the disease the virus produces. Rabies is a virulent virus. Everybody dies from it once they start getting symptoms. Rhinovirus infection (common cold) isn't very virulent. We use CFR here to describe how virulent this virus is.