On Sept. 11, 2001, the U.S. Centers for Disease Control and Prevention (CDC) learned of a domestic terrorism attack via inhalational anthrax sent through the U.S. Postal Service (USPS) mail.

In September and October 2001, at least five envelopes containing significant quantities
of Bacillus anthracis (also referred to as “Ba”) were mailed to United States Senators Patrick
Leahy and Thomas Daschle in the District of Columbia, and to media organizations located in
New York City and Boca Raton, Florida. The attacks resulted in 22 cases of anthrax—eleven inhalational and eleven cutaneous—five of which were fatal.  A total of 21 USPS facilities were contaminated in the attacks, and 32,000 potentially exposed persons initiated post-exposure prophylaxis.

Thirty-five postal facilities and commercial mailrooms were contaminated. The presence of Bacillus anthracis was detected in seven of 26 buildings tested on Capitol Hill. From October through December 2001, the Laboratory Response Network tested more than 120,000 clinical and environmental samples for the presence of Bacillus anthracis. The U.S. Postal Service closed two heavily contaminated processing and distribution centers (“P&DC”): Trenton P&DC, located in Hamilton, New Jersey; and Brentwood P&DC, located in Washington, D.C. The Brentwood facility, closed on October 21, 2001, did not become operational again until December 22, 2003. The Trenton facility, which was closed on October 18, 2001, reopened on March 14, 2005. More than 1.8 million letters, packages, magazines, catalogs, and other mailed items were quarantined at these two facilities. The Environmental Protection Agency used $27 million from its Superfund program to pay 27 contractors and three federal and state agencies for the cleanup of the Capitol Hill facilities.