DHS: anthrax attack remains a "serious threat"
"The threat of an attack using a biological agent is real and requires that we remain vigilant," Polk said. "A wide-area attack using aerosolized Bacillus anthracis, the bacteria that causes anthrax, is one of the most serious mass-casualty biological threats facing the US."
Polk went on to note that anthrax is nearly 100 percent fatal without treatment, and pointed out that "a successful anthrax attack could potentially encompass hundreds of square miles, expose hundreds of thousands of people, and cause illness, death, fear, societal disruption and significant economic damage."
Anthrax is considered a major threat because it can be easily produced in vitro and aerosolized. In 2001, letters containing anthrax were mailed to two Democratic senators and several news offices, infecting 22 and killing five.