Real life situations. Fantasy worlds.

This idea is something that came to me through a variety of sources; many of which really don't add up when I write (type) them.  In the interest of getting to the point I don't plan on breaking it down but if you really want to know the inspirational elements let me know.  A condensed version would be "when magic is not enough".

So.  This is D&D focussed as I'm kicking off a D&D Next playtest game just now so a lot of my game ideas are going into that bucket.

• Setting:  Fantasy city.  Something the scale of York in England but coastal.  Thriving fishing economy and busy port for traders of all kinds.
• Situation: Disease / Plague.  Over the past 2-3 months an illness has spread amongst the people of the city.
• What's unusual?: The disease is only affecting Humans and only those under the age of 40.  The more unusual element however is that it's starting to spread across race with Elves, Dwarves and other races starting to experience similar symptoms...
• What's been tried?:  The Clerics of a variety of churches have called upon the Divine power to cleanse the city of the disease.  Spells work but only on individuals.
• Why didn't that work?:  The disease is spreading quicker than the Clerics can heal.  For every 50 people healed another 60 are infected and that ratio is getting worse for the Clerics.  Despite more coming to heal the disease continues it's march through the residents of the city.
• How do the players get involved?:  TBC.  I have a variety of ideas but given that I actually plan to use this as a kicker for a game I'm going to hold fire on revealing too much.  Ultimately though the situation is dire and it doesn't look like it's going to slow down any time soon so it'll be a race against time to do something...
• Who's behind it?: The immediate problem of the disease has been perpetrated by someone with strong ties to the city.
• Who do they work for?: Someone who has a vested interest in seeing the city fall but also more importantly certain individuals to fall along with the city.
• Who do they work for? 2: Ah yes, there's always a big bad right?  Well maybe not always but in this case, that'd be a yes.
• What's the answer?: Essentially this question is "What is the macguffin?"  Again because I plan on using this in-game I'm not going to give it all away here.  Ultimately though the answer to the disease is to find a cure. What form that cure takes though may be a surprise...

The options around this are quite large but the key to the plot is that the clock is ticking so the party need to get their act together and quickly.