Secret US Germ Testing Program in the 1950s.

From the website:

Fifty years ago, American scientists were in a frantic race to counter what they saw as the Soviet threat from germ warfare. Biological pathogens they developed were tested on volunteers from a pacifist church and were also released in public places.

See more at BBC’s article about its documentary (called Hotel Anthrax) on America’s secret germ program: Link