Serratia is a bacterium that some doctors and residents of the [San Francisco] Bay Area have been familiar with for many years. In 1950, government officials believed that serratia did not cause disease. That belief was later used as a justification for a secret post-World War II Army experiment that became a notorious disaster tale about the microbe. The Army used serratia to test whether enemy agents could launch a biological warfare attack on a port city such as San Francisco from a location miles offshore. For six days in late September 1950, a small military vessel near San Francisco sprayed a huge cloud of serratia particles into the air while the weather favored dispersal. Army tests showed that the bacterial cloud had exposed hundreds of thousands of people in a broad swath of Bay Area communities. Soon after the spraying, 11 people came down with hard-to-treat infections at the old Stanford University Hospital in San Francisco. By November, one man had died. The outbreak was so unusual that the Stanford doctors wrote it up for a medical journal. But the medics and [the dead man's] relatives didn't find out about the Army experiment for nearly 26 years, when a series of secret military experiments came to light. Some people now speculate that descendants of the Army germs are still causing infections here today. The secret bio-warfare test might have permanently changed the microbial ecology of the region.