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.
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. |
Additional Photographs
|