I found this one in a delightful little book of essays about books that should be required reading for *all* members of this forum () - Ex Libris - Confessions of a Common Reader by Anne Fadiman.

Anyway, my dictionary defines this as:
n. Pathol. an acute, febrile infectious disease, caused by a specific streptococcus, characterized by diffusely spreading deep-red inflammation of the skin or mucous membranes. [ME erisipila < L erysipelas < Gk = erysi- prob. akin to erythros red + -pelas prob. skin, akin to pelma sole of the foot; cf. L pellis skin]

Two questions ~ is this actually cited as a diagnosis, or is the patient more typically told "You have a form of strep"? Also, is the erythros given in the eytmology relative somehow to the name of the penicillin alternative erythromycin? My dictionary gives no etymological justification for that one...