Meaning: a generic disease, often used to describe flu of various sorts.
Usefulness: 1 (When you have one, as I do. Doctors talk vaguely about viruses, but we all know they mean lurgi.)
Logofascination: 1 (Possibly invented by the Goon Show, this word has been particularly useful to diseased bloggers: the Inky Fool considered its possible origins, and Lynneguist linked to a comprehensive World Wide Words post and a video on cooties. I'm interested in the spelling issue - the Goons spelt it lurgi, as I normally do, but the OED has lurgy. Here's hoping those links will keep you busy, as I may need a night or two off to do battle with it.)
In the wild: Mainly in the UK, and dying out in books, if ngram is to be believed.
Connections: lurgy - fever lurden - lither lurden - lither (I could've done 2, via fever, but the 'fever lurden' / 'lither lurden' link need a mention. Lurden means lazy, as does lither, after softening from its original meaning of wickedness. Fever lurden is the disease of laziness, whereas a lither lurden is a lazy, lazy person.)
Which is used in: G&P, Book the First (Gargantua), XL: Why monks are the outcasts of the world; and wherefore some have bigger noses than others.
After the same manner a monk--I mean those lither, idle, lazy monks--doth not labour and work, as do the peasant and artificer; doth not ward and defend the country, as doth the man of war; cureth not the sick and diseased, as the physician doth; doth neither preach nor teach, as do the evangelical doctors and schoolmasters; doth not import commodities and things necessary for the commonwealth, as the merchant doth. Therefore is it that by and of all men they are hooted at, hated, and abhorred.Rabelais does defend some monks, but if his characters are anything to go by, he preferred them hard-drinking and tough-talking. Sir Thomas has expanded Rabelais' one word (oiseux) into three (lither, idle, lazy) - to be fair, if you read enough Cotgrave, you develop a fascination with synonyms. Cotgrave on oiseux:
Lither, sloathfull, sluggish, full of idlenesse;