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US postal service puts anthrax detectors to the test

Naturevolume 417page579 (2002) | Download Citation


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Automated anthrax-sniffers will be making their debut in selected US post offices this summer. The US Postal Service (USPS) is already testing the equipment with an eye to installing it nationwide in all of its 400 or so mail-sorting facilities by next year.

The USPS hopes that the equipment, which detects the DNA of the anthrax bacterium, Bacillus anthracis, will prevent, or at least mitigate, the effects of any future bioterrorist attacks through the mail. In last October's attacks, anthrax spores contaminated several post offices after being dispersed into the air by mail-sorting machines, killing two postal workers.

A $3.7-million trial to be carried out at several sorting offices on the east coast will test a detector produced by Northrop Grumman, an aerospace contractor based in Baltimore, Maryland. The device continuously channels samples into a detection unit that screens for DNA from the anthrax bacterium.

A similar device designed by Lockheed Martin has not yet entered field tests. Whichever system is chosen will be installed nationwide and paid for, in part, by $200 million in emergency funding that Congress set aside last autumn for the project.

The detectors in Northrop Grumman's system are made by the biotechnology company Cepheid of Sunnyvale, California. They rely on the polymerase chain reaction (PCR) to single out and amplify regions of DNA found in the toxicity gene of anthrax. A molecular tag turns fluorescent if it finds amplified DNA fragments to bind to, activating the alarm within half an hour of sample collection. If the gene is not present, no DNA is produced. A worker would periodically replenish the disposable reaction chambers in the detector, but the system requires little other maintenance.

All detection systems carry a risk of crying wolf with 'false-positive' results. Cepheid operations chief Kurt Petersen says that controls built into the PCR system should minimize these, but they won't know for sure how well they work until the tests are complete. For example, the system could run a second test to confirm a positive result before a facility is evacuated. “We are entering a realm of DNA testing that has never been done before,” he says.

The trade-off in eliminating false positives is missing some genuine positives, says Martin Blaser, a microbiologist at the New York University Medical School who has studied last October's anthrax attacks. But he says it is better to risk missing some traces of anthrax than to panic postal workers and erode their trust in the system by raising too many false alarms. “We won't be able to develop a system that will protect everybody,” he warns.


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