We've heard spinning Rats state the Senate strain was a "potent" Anthrax, but has that been confirmed by anyone who'd recognize the difference between natural and bioengineered Anthrax, such as Ft. Deitrich? I'd guess that wild anthrax spores would come in a bell curve of size ranges. A random few would be able to go airborne and enter the lungs and nose and could produce the symptom free positive nasal swabs being reported for most positives. With enough exposure and bad luck wild Anthrax can produce pulmonary anthrax, a.k.a. "Woolsorter's disease." After all, about 17 such cases happened in the last century, primarily in people working with contaminated hides and wool.
The number of outbreaks makes it obvious someone is delivering Anthrax with evil intent. Occam's razor suggests Iraqi or former USSR biowarfare links, but until reliable experts, i.e. someone other than Rat politico types, confirm this bug is unnatural we can't rule out that bin Laden's group did this alone or even that some other nutcase group is the cause. Ft. Deitrich should be able to decipher this quickly; whether they'll tell us the results is another question.
The first factor is the type or strain of the antrhax itself. The case in both Florida and NBC was the Ames strain, which was originally developed in Iowa in the 1950s. This is the "medical grade" antrhax used in research into vaccination and treament, and is one of the base strain which the military then tries to modify through genetic engineering or selective breeding. This discovery makes it utterly impossible that is "wild" anthrax. However, this particular strain is also the most widely spread of the man-made strains which is why it's more difficult to trace. The Daschle attack hasn't been ID'd yet, but there are reports that it is sensitive to pennicillin, which is consistent with the AMES strain, and would be unlikely to be a military strain.
The size of the anthrax also affecticts its lethality. I have not heard any reports on the size of Dascle's anthrax. Changing the size of the anthrax is partly biological and partly mechanical. It takes a bit of training and some expensive equipment; this is not something that you could do in a hotel room. I don't know how this process works but I've been told that anyone with a degree in biology would be able to figure it out.
The third case, and the other feature commonly called "militarization" makes the antrhax easier to inhale. In it's natural state, Antrhax [of any strain] tends to clump together, making it too large to be effective. There hasn't been any official word on whether Daschle's antrhax was treated in this way, but the simple fact that a large number of people were exposed from a single source makes a lot of people suspicious. The silver lining is that this process is the most difficult part of creating "weapons-grade" antrhax; just a few countries have been able to solve this problem and furthur, IF this anthrax has been treated this way, we will be able to tell which country it is from based on what solution was used.
A final note should be made about the amount of antrax. Most of the attacks have been made with "a powder containing anthrax." This attack was made with "a powder which was antrhax." So the terrorists used a much larger number of bacteria spores in this attack than they uesd in the others. Which says nothing about where it came from, but may indicate that they have a very large stockpile.