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Anthrax testing: Not for everyone

By KATIE LEISHMAN, UPI Science News

The spreading anthrax scare has thousands of people across the country calling public health offices about testing and officials say there is widespread misunderstanding about how the disease is diagnosed and who should be tested.

New reports of people who developed anthrax infection despite having no obvious exposure to the pathogen have increased the demand for testing.

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"In people, the purpose of testing is simply to confirm a clinical diagnosis of anthrax in a patient with symptoms consistent with anthrax," Dr. Norman Crouch, director of the Minnesota State Public Health Laboratory, told United Press International in a telephone interview.

"When you tell the public that there is no screening test for anthrax, that there is no test that can definitively tell them if they have been exposed or infected or should be treated, they think you are holding something back," Crouch said. "In fact, we just want to spare them unnecessary testing."

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Crouch is sensitive to the confusion as people daily hear about various tests on television news shows or read about them in newspapers.

"The test most people read about is the nasal swab. Yet it isn't even a diagnostic test," he said. "It simply reveals whether there is anthrax in a particular environment, meaning that people there might be exposed or infected."

The Minnesota State Health Department, in conjunction with the Centers for Disease Control and Prevention in Atlanta, recommends testing only once a person has developed symptoms.

However, anyone who has been in a facility or at site around the time anthrax spores were confirmed there is advised to begin a 60-day course of antibiotics immediately. Officials said they should watch for any suspicious lesions, flu-like or gastrointestinal symptoms and contact a physician immediately if any such symptoms develop.

Many people in affected offices and facilities have had blood tests designed to detect antibodies against anthrax. The detection of antibodies can reflect an immune response to an infection but does not necessarily mean someone will develop the disease. Moreover, it can take a week or more to mount an antibody response, so sometimes two consecutive blood specimens may be collected two weeks apart.

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"An increase in the level of antibodies between the two specimens may suggest an active infection," Crouch said. He cautioned, however, "some people who are infected may never produce antibodies at all."

The reliability of the blood test may be reduced if administered once a person has started antibiotics, which can affect the number of organisms present in the body.

Once someone develops symptoms consistent with clinical anthrax, however, testing is standard.

"The testing is conducted to be sure the diagnosis is accurate, not to determine the choice of drug. Ninety-nine percent of anthrax strains are sensitive to penicillin," said Gary Andersen, a senior scientist at the Lawrence Livermore National Laboratory in Livermore, Calif.

Few scientists know the testing process for patients with suspicious symptoms better than Dr. Richard Meyer, director of the Bioterrorism Rapid Analysis and Advanced Technology Laboratory at the CDC.

"There are two issues from the start: sampling and testing. A test can be no better than the clinical specimen, which needs to be properly collected and taken from a well-chosen site," Meyer said.

Samples of blood, skin or spinal fluid can be collected. First a lab performs the so-called rapid tests, beginning with a polymerase chain reaction or PCR test, in which DNA from a detected organism is amplified and probed.

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The test is "exquisitely sensitive," according to Meyer, and can reveal within an hour or two whether anthrax DNA is present in a specimen. This rapid test is not considered confirmatory, however, but simply preliminary.

"The lab is not diagnosing the patient, simply assessing a specimen for the presence of anthrax," said Meyer.

The samples also are put in culture so any bugs can be grown up, which can take up to 24 hours. Tests to distinguish between anthrax and closely related organisms may be next. The bacteria also can be examined for motion or motility -- anthrax is non-motile -- while many of its close cousins are motile.

Once the features of the detected organism are assessed, two more tests are done, the first a gammaphage analysis.

"For every bacteria there is a virus that specifically infects it, called a bacteriophage," Meyer explained. "So a laboratory smears some of the cultivated organism on a plate. Then a drop of the liquid bacteriophage is added."

A day later, there should be a clear spot where the bacteriophage was added, indicating the virus had destroyed the anthrax.

In addition, a fluorescent antibody staining test, with antibodies specific for anthrax, also is done on the detected organism. The staining test in combination with the gammaphage analysis are considered to be the confirmatory tests. If both are positive, the patient is said to have anthrax.

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Additional testing may be done on the isolate from the patient, comparing it to isolates from other known cases, but such testing is forensic rather than clinical, conducted in hopes of discovering where that isolate may have come from.

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