[londons_explore]

My guess:

It's a new virus or prion disease.

These 50 people probably all ate meat from the same cow in a hot dog 10 years ago. That hot dog or source cow will never be identified because humanity doesn't keep a sufficiently traceable record of such things, even though it would save lives to do so.

It probably isn't transmissible between people, so there will be a few hundred more cases of this over the next 20 years, and then it'll disappear.

[t00ny]

« On the surface, the illness seems to resemble a prion disease—neurological disorders caused by rogue proteins that accumulate in the brain and slowly destroy it. But medical examinations haven’t found any evidence of prions in these patients so far. Prion diseases are also universally fatal, usually within months to a year after the first symptoms appear, but symptoms of this condition have developed over 18 to 36 months in the patients found so far, while five people with the condition have died. »