Is the diagnosis that definitive? Recall Dr. Gerald Weisfogel. He is the NJ cardiologist who suspected that he might have contracted the first case of anthrax, since he recalled having a black lesion consistent with cutaneous anthrax around Sept. 4; at the time, he thought it was a spider bite. The CDC tested his blood, and it proved negative for anthrax after all. (I'm not sure if this means testing for antibodies to anthrax, but I imagine a test after the fact has to be something like that.)
On the other hand, an interview with a CDC representative states that the test used in the Weisfogel case is "not validated for clinical use" and that they are "learning about their meaning and how to interpret them, but this test, in and of itself, is not usually as helpful as some of the other ways we have of diagnosing or excluding the diagnosis." So it's conceivable that Weisfogel did have anthrax, although the odds are against it.