I always thought "miasms" were an older concept in medicine, a theory about chronic and congenital disease.

The word comes from "miasma", which is a cloud of vapour or noxious gasses which literally hangs over a swampy area like a cloud of its own pollutions. The image itself brings to mind all those swampy, malarial places--which would be a kind of miasmatic illness in itself.

Divina