Sir.—At least three recent articles1-3 have referred to erythema infectiosum as fifth disease. Fourth disease, Duke Filatow's disease, is now known to be mild atypical scarlet fever, but it is doubtful if anyone in this generation has even made this diagnosis. Accordingly, there is no fourth disease, so there cannot be a fifth disease.
In the 1930s when John Branch Cabell was widely read, he described a character who was admitted to heaven because he claimed to be Pope John XXI, only to be kicked out when it was discovered later that there never was a Pope John XX. I hope the example is not too strained, but fourth disease is similarly apocryphal and, if no fourth disease, hence, no fifth.
I suggest that fourth disease be deleted from our lexicon and fifth disease along with it, and restored only if someone can remember what first, second, and