DATE OF ANTHRAX ONSET BY SOURCE OF EXPOSURE

The first two letters were postmarked on Tuesday, September 18.  No source letter was found for three persons in the first wave, but likely came via a September 18th mailing.  Two persons who appear in the second wave had contact with a September 18 letter during October 12-15, many weeks after it was received in their office.  The second wave most likely had contact with the Daschle letter, postmarked Tuesday, October 9, or the Leahy letter, later found to have been sent on the same day but forwarded by mistake to the State Department on Monday, October 14, where case 20 became infected.  Case 23 was most likely infected through cross-contamination with a letter that had been processed October 9 in Trenton, New Jersey but was handled latter. There is no definite link to explain case 22, although possibly (click for more) there was contact with disposed September 18th letters (similar to cases 19 and 21), or with mail cross-contaminated by contact with the October 9th letters.

The case-fatality among the 8 cases known to be exposed to a September 18 mailing was 0%, while among the 10 cases with known exposure to the October 9 letters, the case-fatality was 20%.