Con-spray-a-sea

In the '50s, the US Navy secretly released a massive cloud of harmless red bacterium into San Francisco, attempting to discover how effectively a biological weapon could be deployed silently in population centres.^[1]

The bacteria, in fact, spread kilometres inland, and made its way indoors via ventilation or other small openings. The Navy took swabs and used air sampling devices,^[2] estimating that nearly all the residents of San Francisco were exposed. This experiment, named Operation Sea Spray, was successfully kept under wraps at the time, and was revealed only in the 1970s.^[3] Pretty successful, right?

There was just one flaw. The bacteria, Serratia marcescens, wasn't actually harmless. In fact, it is an opportunistic bacteria that can harm newborns, those with intravenous lines, and people with compromised immune systems. Consequently, 11 people developed very rare urinary tract infections, with one passing away from a heart infection.^[4] Some doctors theorised that it could also have explained increased cases of pneumonia, heart valve infections and serious infections for drug users in subsequent years.^[5]

Even after the medical experts had documented it as a pathogen,^[6] the UK government carried out a similar, secretive test against its citizens in the 1970s.^[7]