"Epidemiology" and "Public Health" Aren't the Same Thing

I keep having to discuss the differences between the two with people, so I might as well write a short piece on it that I can just point to.

"Epidemiology" is "the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined populations."

"Public health" is  the application of action and policy to the goal of reducing the incidence and spread of disease and other negative health outcomes.

Yes, "public health" may be informed by epidemiology (and other sciences and disciplines), but public health is not those other things.

John Snow figuring out that the Broad Street cholera outbreak was associated with a particular well was "epidemiology."

John Snow persuading the Board of Guardians of St. James's Parish to remove the pump handle from the well was "public health."

So, here's the problem:

To the extent that "public health" involves policy, it also involves politics. And whenever politics is involved, science gets skewed, misdirected, or even falsified to serve the agendas of politicians.

Take, for example, the Third Reich's "racial hygiene" laws -- everything from ridding the German gene pool of mental disability through selective euthanasia to ridding German society of typhus by ridding German society of Jews. That was "public health" in action, with bad (in fact, often entirely fake) "science" as its justification.

Yeah, I know. Godwin's Law and all that. But it is an indisputable fact that the last year has seen epidemiology and other branches of science abused in much the same way.