Did terrorists attack Washington with a deadly pathogen?

On Sept. 24th, tens of thousands of protesters marched past the White House and flooded the National Mall near 17th Street and Constitution Avenue in what may have been the biggest antiwar rally since Vietnam. Unknown to the crowd, biological-weapons sensors scattered across Washington were quietly doing their work. Sometime between 10 a.m. on Sept. 24 and 10 a.m. on Sept. 25, six of those machines sucked in trace amounts of deadly bacteria called Francisella tularensis. Why haven't we heard more about this?