How are buildings examined for possible anthrax contamination?

Does an announcement that no anthrax was found mean with certainty that none is there?

_William H. Grubbs

Chesterfield, Mo.


Among the first respondents to a report of an anthrax threat are hazardous materials units dispatched by local, state, or federal agencies. They work with law enforcement officials to examine buildings and investigate envelopes and packages that are suspected of containing toxic substances. One of their first tasks is to collect the sample that represents the initial threat and send it to a laboratory for testing.

During testing, anthrax spores can be grown like seeds. They sprout and multiply and then are evaluated under a microscope. Polymerase chain reaction (PCR) tests can amplify trace amounts of DNA to help document whether the anthrax bacterium is present, and direct fluorescent assay (DFA) tests can detect key anthrax proteins.

The sampling method depends on whether the spores are airborne or not. Anthrax spores vary in size; spores smaller than 10 microns in diameter are more likely to become airborne. The airborne anthrax spores found in Senator Tom Daschle's office, for example, were 1.5 to 3 microns in diameter.

Airborne anthrax spores can be collected by air-sampling equipment. Hazardous materials squads use a special type of vacuum cleaner called high-efficiency particulate air (HEPA). This device employs special filters to trap spores that are 0.3 microns in diameter and up. Hazmat teams use swabs to sample heavier spores.

Experts also try to define the path of the original anthrax threat. If it is a letter, for example, then samples will be taken around the path of that letter. "It depends where the mail piece has traveled and how much equipment it has gone through," says Gerry Kreienkamp, a spokesperson for the United States Postal Service. "There are a lot of variables."

Workers on hazardous-materials teams take a series of samples, moving inward in concentric circles toward the suspected anthrax exposure. "Experts may take samples every quarter-mile," says Bethany Grohs of the Environmental Response Team at the United States Environmental Protection Agency. "Then, when they hit a hot spot where they find spores, they may take 50 samples in a much smaller area until they are sure they have gotten it all."

An announcement that no anthrax was found means that a location or building has been tested and the tests conducted showed no signs of anthrax. Because of the nature of anthrax and how it spreads, however, experts can never be 100 percent certain they found all the spores. "I really think we are taking as many samples as we can," says Grohs. "Nothing is perfect but there is very little anthrax we don't get to."