Don't you think that if Atta, Allah, Achmed, or Abdul were handling anthrax that they would have been taking preventive cipro or similar protective antibiotics , as to not get sick and draw attention to what could have otherwise been a viscious surprise anthrax attack? For this reason I feel that anthrax will be a home grown problem.
I'm glad you asked that.
In August 2001, Atta and Al-Shehhi, the two WTC pilots, went into Huber Drugs in (I think) Delray Beach, FL. Most of the attention regarding this visit has been focused on Atta's complaint of raw, chemically-burned hands.
But I have always been fascinated by Al-Shehhi's complaint during the same visit: He complained of an apparent bad chest cold, and was directed to a walk-in medical clinic next door. He returned with a prescription for an antibiotic.
This clearly indicates that the 9/11 hijackers were not on antibiotics to start with, even after Al-Haznawi's June 22 or 23 emergency-room visit. Why this was calls for speculation. I would guess that there was an accident or an early mishandling of the material; the envelopes were probably not to be touched until just before 9/11, when infection would no longer be a problem.