Possible Explanation For Mysterious Anthrax Deaths

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Possible Explanation For Mysterious Anthrax Deaths

By Merritt McKinney

5-13-2

NEW YORK (Reuters Health) - A new mathematical model provides a possible

solution to the mystery of how some people in the US were infected with

anthrax last fall despite having no known direct contact with contaminated

mail.

" The anthrax attack on the US postal system last fall revealed a far greater

threat to our society than might have been recognized previously, " Dr. Glenn

F. Webb of Vanderbilt University in Nashville, Tennessee, told Reuters

Health. Webb developed the model along with Dr. J. Blaser at New York

University School of Medicine.

Even though only a handful of anthrax-laced letters are thought to have been

sent, due to " cross-contamination " during the sorting and delivery process,

many more people were exposed to possible inhalational anthrax infection,

according to the Vanderbilt researcher. " Our model simulations indicated

that there were approximately 5,000 such letters cross-contaminated by the

original six contaminated letters, " he said. " The large numbers of

cross-contaminated letters pose a very serious risk for our entire postal

system, " Webb added.

Since last fall, there have been 22 cases of anthrax in the US--11 by

inhalation of anthrax spores and 11 by skin contact with anthrax. The

infected included 11 postal workers and 7 others who were infected by mail

delivered to their work. How the remaining four people, including two older

women who died from inhalational anthrax, came into contact with anthrax has

been uncertain, however.

The model devised by Webb and Blaser tracks the anthrax-laden letters

through the postal system, starting with the mailbox or post office, moving

on to local and regional postal stations, and then back to local stations

before delivery to homes and offices. The researchers calculated that

envelopes could have leaked anthrax while passing through mail-processing

machines in postal stations.

These spores could have then been deposited on or inside other envelopes

passing through the machines. The model estimates that each of the

envelopes, which presumably contained trillions of anthrax spores each,

could have contaminated thousands of other letters. The number of spores in

these cross-contaminated letters would be expected to be much lower, of

course.

In the model, Webb and Blaser estimate that contaminated letters contained

10 to 10,000 spores each. If so many letters were contaminated, then why did

fewer than two dozen people develop anthrax? In most cases, the

cross-contaminated mail probably contained too few anthrax spores to make

people sick, according to the authors.

In addition, the elderly are much more vulnerable to anthrax infection than

younger people. Webb and Blaser point out that the model does not prove that

the exposure to letters cross-contaminated with anthrax killed the two

elderly women whose anthrax exposure is unknown. Another explanation, they

report in the May 14th issue of the Proceedings of the National Academy of

Sciences, is that the two women inhaled airborne anthrax spores that blew

from the postal facility in Trenton, New Jersey, where some of the anthrax

letters were processed. They note that on October 9th, winds were blowing

from Trenton directly toward the cities where the women lived, New York City

and Oxford, Connecticut.

The model does, however, " provide a framework " for analyzing the possible

spread of anthrax by way of the mail, according to the report. Based on the

model, Webb and Blaser conclude, " The rapid and widespread usage of

antibiotics among postal workers and persons in the immediate environment of

the received original letters probably averted a substantial number of

cases. " To prevent future cases, the mail sorting and delivery process

should be studied to determine ways to prevent cross-contamination, the

authors advise.

An approach worth considering, they note, is the vaccination of postal

workers and other people who handle mail. In the meantime, they recommend

that postal workers undergo regular blood tests to look for anthrax

infections. Blaser told Reuters Health that the problem is not restricted to

the US. Sounding a positive note, however, he added, " The type of analysis

developed should make it easier to track and contain future events should

they occur. "

SOURCE: Proceedings of the National Academy of Sciences 2002;99:7027-