A letter addressed to Senator Patrick Leahy was found by FBI and Environmental Protection Agency (EPA) hazardous materials personnel on Friday, November 16. The letter was in one of the 280 barrels of unopened mail collected from Capitol Hill after an anthrax-contaminated letter to Senator Daschle was first discovered. An innovative protocol was developed by scientific and forensic experts to analyze these congressional mail bags for anthrax contamination. The new method eliminated the need for hazardous materials teams to sift through each piece of mail in the 635 trash bags to find additional contaminated mail.
Safety was the primary consideration of the entire operation.
Although the level of contamination was not known beforehand, the work
space and sampling procedures were designed so that the risk of exposure
would be minimized even if the mail were heavily contaminated. And,
everyone in the containment area would wear personal protective equipment
and respirators as seen in the figures. The mail was sampled and sorted
in a containment facility constructed within a large warehouse.
To ensure that bacterial spores would not escape into
the surroundings, the containment facility was maintained with negative
air pressure, and intake and exhaust air was filtered with high efficiency
particulate air (HEPA) filters, which trap essentially all particles
the size of anthrax spores. Negative air pressure was achieved by exhausting
air faster than it was let in, which means that, aside from the exhaust
fans, the air always flowed into the room through any small openings
that were present. Work began only after the structural integrity of
the containment facility was approved by inspectors.
Air samplers were used to monitor the air both inside
and outside the containment area, also called the "hot zone." These
samplers help estimate the quantity of airborne spores as well as when
spores are in the air. No spores were detected for the entire operation
in air samples collected in the decontamination area, or the "cold zone,"
which includes the outer work space and outside the air exhausts. On
the other hand, spores were detected from all four samplers within the
hot zone whenever a particularly "hot" bag was handled. The exposure
of workers was further monitored by taking samples directly off of their
clothing. In general, people did not become contaminated unless a hot
bag was handled, and then contamination was sometimes quite high. This
graphically demonstrated the ease with which the spores become airborne,
and underscores the respect with which contaminated material must be
handled.
Seemingly, the most straightforward way to find a letter
that looks like another one is to simply sort through the mail by hand.
However, such an approach would have drawbacks. First, it might unnecessarily
expose workers to high concentrations of spores if a letter was actually
present. Second, it would be time-consuming and extremely tedious, which
might decrease the attention to detail that would be needed for a thorough
search. And third, if an anthrax-loaded letter were present that did
not resemble those sent to Sen. Daschle and Mr. Brokaw, it might be
missed.
The strategy for finding an anthrax-loaded letter in the
mail was also designed to minimize risk. In this operation, simple was
best. The methods used were classic microbiology techniques and the
plan to search through the bags of mail was based on some very simple
ideas. The known behavior of the Daschle letter suggested that all of
the above drawbacks might be overcome by looking for spores rather than
for letters. It was clear that the Daschle letter made numerous people
sick and contaminated large areas wherever it went. Therefore, it seemed
almost inconceivable that a trash bag containing a similar anthrax-loaded
letter would not contain an overwhelming number of spores.
The sampling plan to find the Leahy letter was accomplished
by teams of hazardous materials (Hazmat) workers from the FBI and EPA
Criminal Investigative Division. Each bag, sampled in turn, was jostled
around to mix up any spores present. A swab was inserted into a small
hole in each bag and wiped around the inside. After the swab was withdrawn,
the hole was sealed with duct tape, and the swab was used to inoculate
a Petri dish containing a particular solid growth medium, which was
sent to the Naval Medical Research Center (NMRC) for analysis. Colonies
resulting from the growth of Bacillus anthracis (the anthrax bacterium)
on this culture medium could be easily identified by the experienced
laboratory workers at NMRC.
This plan had a number of advantages. Workers would have
to sample only 635 bags rather than examine many thousands of individual
letters. Sampling through small holes minimized the release of spores
into the work space. The swabbing technique was simple and easily mastered
by the workers. Normally, swabs are packaged and transported to the
laboratory where they are then used to inoculate the culture medium.
Inoculating the medium at the scene greatly reduced the workload on
the laboratory. In addition, the time needed to obtain results was reduced
because the bacteria started growing as soon as they were put in the
Petri dish, producing visible colonies by early the following morning.
Contamination was detected in only about 60 bags. The
swabs from about 50 bags revealed only trace contamination. Seven produced
greater than 100 bacterial colonies from a swab and were considered
"hot." The inoculation of Petri dishes with swabs is a very sensitive
technique that can theoretically detect a single spore. However, the
maximum number of spores that can be identified with this method is
about 300. If more are present, the resulting colonies become too crowded
to count. This leaves very little room to distinguish samples that produced
100 colonies on Petri dishes from those that may have contained many
more than 300. Therefore, a second sampling technique was used to determine
whether or not there were large differences in contamination levels
between bags.
For the second sampling method, air was drawn out of selected
bags for two minutes each and bubbled through water. The water accumulates
spores over time, which can then be counted, no matter how many there
are. This method proved to be much less sensitive than direct plating
onto Petri dishes, but it turned out to be more discriminating. Spores
were detected in the air of only three bags. One bag produced about
100 spores over the two minute sampling time, another, 300, and a third
between 19,000 and 23,000. The difference between this last bag and
all of the others made it clear that, if there was just a single anthrax-loaded
letter, it must be in that bag. To be cautious, all bags that produced
greater than 20 spores from the swabbing method were sorted by hand.
These bags were handled in biological safety cabinets because of the
increased risk associated with opening the bags and handling contaminated
mail. Safety cabinets use directed airflow to prevent contamination
from escaping while work is being done inside of them.
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Time line It is not easy to find places willing to have anthrax operations performed on their property, and it took over a week to identify a facility in which to work. The containment area and associated structures took two weeks to complete to the satisfaction of inspectors. FBI and EPA personnel began sampling the bags of congressional mail on the afternoon of Saturday, November 10. The sampling continued through the next day and into Monday, November 12. All results of the sampling were available from the NMRC laboratory by November 13. The following day, personnel met and identified the bags that would have their air sampled and mail sorted. On Thursday, November 14, air sampling began, as did the sorting of some bags that tested "cold" for anthrax. Mail sorting by FBI personnel began in earnest on Friday, November 16. By 5 PM Friday, the last bag was searched; the Leahy letter was found approximately three-quarters of the way into the bag. |
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