For one week in September of 1950, the US Navy sprayed massive amounts of bacteria (Serratia marcescens)  into the air two miles off the coast of San Francisco, California. The aim of this secret biological warfare experiment was to learn how vulnerable large US cities like San Francisco would be to a biowarfare attack by terrorists.
The bacteria used were Serratia marcescens, which can cause respiratory issues and meningitis, and Bacillus atrophaeus that can be lethal immunocompromised individuals.  At the time, the Navy believed these bacteria were harmless to humans. But when Bay Area residents began rushing to the hospital, it became clear that was not the case. After inhaling thousands of bacterial spores, 11 people checked into Stanford Hospital near San Francisco with very rare, serious urinary tract infections that doctors ultimately determined were caused by the experiment.  
One patient, a man named Edward Nevin who was recovering from prostate surgery at the time, died. 
Now, 75 years later, some Americans fear this may be happening again as they claim an 'unnatural' fog with a 'burning chemical-like smell' has plagued their communities in recent weeks.
@DailyMail