(fandom slang) An illness resulting from having people from a wide variety of places at a single gathering such as a convention, allowing disease to spread easily among them due to lack of immunity.
1999 September 18, Kitchen, Allen, “A proposal for ALFers”, in alt.lifestyle.furry, Usenet[1], message-ID <A6D29FFCD278DB9B.8E59F475769021D7.8D510A7C0C424992@lp.airnews.net>:
Much has been said about those who go to furry and SciFi conventions and return with the "Con Crud."
2002 September 19, Jones, Julia, “Re: US Dentristy and Optometry”, in rec.arts.sf.fandom, Usenet[2], message-ID <BmkrtFJ+Zli9Ewvi@jajones.demon.co.uk>:
The root canal will be done again as soon as I've recovered from my Worldcon dose of con crud.
2003 September 22, diane, “Re: Gatecon report”, in alt.tv.stargate-sg1, Usenet[3], message-ID <20030922013153387+0100@news.btinternet.com>:
any con crud? lots of people seem to have gone down with something, some are still stranded in Vancouver too ill to fly home :-((