Aerialized spores from the drums is likely, but this article doesn't
really incriminate the lettuce. But so be it, CDC may have good evidence for it.
It does remind me of my first (1960's) and worst (potentially) career mistake.
As a graduate teaching assistance for a course in Medical Microbiology,
one of my first assignments was to set up a class exercise to demonstrate "virulence".
That is, how one strain of a pathogenic microorganism can
produce severe disease while another strain does not.
So I wrote a letter on university stationery to Fort Detrick, MD,
the US Army's Center for Biological Warfare, asking for
one culture of virulent- and one of avirulent- B.anthrasus.
Within a few days, the cultures arrived, along with a letter giving the LD50 .
This is the dose (number of cells/spores) it takes to kill 50% of the animals infected.
The LD50 for avirulent strain was something like billions.
In other words, you could not inject enough to kill 50% of the mice.
The LD50 for that virulent strain of anthrax was 1.
This so scared the bejesus out of me and I immediately
autoclaved the entire package for several hours.
It also gave me a lifelong fear of what the military was capable of
doing to "prevent and protect" the US from biological warfare.