Investigators assigned to the case of Kathy T. Nguyen, the Manhattan
hospital worker who died of inhalation anthrax last week, are confronting
some disquieting possibilities as to how she might have become infected.
One, which has aroused keen interest among investigators, is that at some
point in her well-ordered, fairly restricted life, she crossed paths with a
perpetrator of the attacks and his product.
If that is the case, reconstructing Ms. Nguyen's movements, as
investigators are trying to do, could lead to the source of the spores.
Another possibility, more threatening to the public, is that Ms. Nguyen
was somehow infected by spores from a tainted envelope, but with a dose far
smaller than the minimum generally thought to be needed for infection.
Except for Ms. Nguyen, those who have contracted anthrax have had some
obvious point of contact with the spore-laden letters and can reasonably be
assumed to have inhaled a significant amount of spores.
But this is not the case with Ms. Nguyen. Nothing in her home or mail or
place of work at the Manhattan Eye, Ear and Throat Hospital contained any
trace of anthrax spores, investigators say.
Dr. Jeffrey Koplan, director of the federal Centers for Disease Control
and Prevention, said yesterday, ''It would take a lot more than a few spores
to cause exposure anthrax.'' And New York City investigators have previously
said that they were looking for opportunities Ms. Nguyen might have had to
come in contact with a large quantity of spores.
But some experts contend that just a few spores, maybe even a single
spore, could infect a susceptible person in rare circumstances.
Could Ms. Nguyen have breathed in a stray puff of spores wafting through
Manhattan's canyons? The lethal dose for anthrax is often said to be 8,000
to 10,000 spores. But that is in fact the amount needed to kill 50 percent
of a population of monkeys. No one knows the smallest number of spores it
would take to kill just 1 percent of a population -- the experiment would
require hundreds of monkeys -- but it could be just a couple of hundred
spores.
Human lungs hold 500 million miniature compartments where the blood
exchanges gases with the air. Each of the 200 spores is likely to be inhaled
into a different compartment and would have an independent chance of
infecting the body, said Dr. Matthew Meselson, a biologist at Harvard
University. In his view, a single spore has a chance, however small, of
infecting someone.
The Army's chief infectious disease specialist during the war in the
Persian Gulf, Dr. Craig E. Smith, who is now at the Phoebe Putney Memorial
Hospital in Albany, Ga., agreed.
The idea that one spore can be enough for infection is somewhat at odds
with the view often expressed by officials at the Centers for Disease
Control and Prevention that there is a threshold, or cutoff number of
spores, below which no infection can occur. But the one-spore theory would
make more understandable a case like Ms. Nguyen's in which no obvious route
of exposure has yet come to light.
''Should we be alarmed that she's an outlier for whom no obvious
connection exists?'' Dr. Smith asked. ''I do find that alarming because it
implies she had a very small inoculum.''
Another possible explanation for Ms. Nguyen's case is that she passed
near some unidentified source of anthrax, like a house, office or laboratory
where the anthrax spores used in the two attacks were being prepared.
If the anthrax was home-grown, the responsible person is presumably well
trained in medicine or microbiology or pharmaceutical manufacturing.
Dr. Smith said that one way of finding such a person would be to test
suspects' blood for antibodies to anthrax. People brewing anthrax spores are
likely either to have vaccinated themselves beforehand, or to have become
sufficiently exposed to have raised antibodies even if they were taking
antibiotics as protection, another expert said.
''If I'd taken 100 people into custody as potential terrorists, I would
have taken a blood sample from every single one,'' Dr. Smith said. ''If
anyone came out positive, that would mean they had had a natural exposure to
anthrax or had been vaccinated, which I think would be evidence they had a
premeditated plan to disseminate anthrax.''
Dr. Anthony S. Fauci, director of the National Institute of Allergy and
Infectious Diseases, said that testing suspects, like those being detained
by the Federal Bureau of Investigation in connection with the Sept. 11
attacks, ''is certainly something that is quite reasonable to consider. The
presence of antibodies to anthrax might indicate if these individuals had
been vaccinated to protect them.''
A court order is needed to compel suspects to give blood samples for
laboratory tests.
There is no sign so far that the F.B.I. has considered screening suspect
populations for the presence of antianthrax antibodies in their blood. An
F.B.I. spokesman dismissed the issue as ''a medical question.''
Federal investigators apparently did not use the precise methods of
serological testing, but instead relied on a far more subjective approach,
handwriting analysis, to explore the possible connection of a man from
Hamilton Township, N.J., to the three anthrax letters.
Many of the people being detained by the F.B.I. are being held on alleged
violations of immigration law, but legal experts said they had not heard of
blood samples being requested from the detainees.
''I am not aware of that,'' said Lucas Gutentag, director of the
immigrants' rights project at the American Civil Liberties Union. But he
said that given the secrecy surrounding the investigation, ''Even seeking a
court order to seek a blood sample would not necessarily be disclosed and
could be conducted in a closed judicial proceeding.''
Mass screening of suspect populations, like the detainees, or people on
the mail-collection route of a Trenton postal worker who contracted anthrax,
or any group that Ms. Nguyen might have met, would raise legal issues, and
even a voluntary request for blood might be seen as coercive. Mass screening
with DNA fingerprinting has been used occasionally in Britain.
Dr. Michael Osterholm, a bioterrorism expert at the University of
Minnesota, said it was important for investigators to keep their minds open
to all possibilities. Ms. Nguyen's case was ''an epidemiologist's
nightmare,'' Dr. Osterholm said, because she lived alone with few close
contacts and died before she could be interviewed. This landscape without
clues was made even harder to read by the long incubation period of anthrax
spores, he said.
Copyright 2001 The New York Times Company
