Science denialists and quacks love to abuse Koch's postulates to deny that various microorganisms are the true cause of disease; so it was inevitable (and no surprise) that they're doing it for #COVID19. https://respectfulinsolence.com/2020/12/18/quacks-misuse-kochs-postulates-to-deny-covid-19/

It is amusing but also very depressing how quacks seem to think that the study of pathogens was frozen in amber at the end of the 19th century. They do so love to cite 19th century understanding of microbiology as the be-all and end-all of germ theory.

It’s not just germ theory deniers, either. Creationists often seem to think that evolutionary biology ceased to advance after Darwin. https://twitter.com/rootiiij/status/1339991972828725249

I wonder: Is there another scientific field like microbiology and evolution, in which denialist cranks think that if they can find mistakes or holes in 19th century (or even earlier) science the will discredit the entire field?

D'oh! How could I have forgotten? How could I have failed to mention cancer research, given how there are people who think that the trophoblastic theory of cancer is still a thing? (It was abandoned nearly 100 years ago.)

Then there's "autointoxication" theory, the idea that disease is caused by "self-toxicity" resulting from a backup of feces in the colon? 120 years ago, surgeons removed colons and dentists pulled all the teeth to "cure" mental illness...