http://www.post-gazette.com/headlines/20011016testing1016p4.asp

Anthrax testing shaky; current techniques not designed for speedy, emergency diagnoses

Tuesday, October 16, 2001

By Rick Weiss, The Washington Post

The bacterium that causes anthrax is a hearty, fast-growing microbe that is relatively easy to isolate and identify from the blood and tissues of people who have fallen ill with the disease. But the bacterium can be difficult to detect at the earliest stages of exposure or infection. And some of the tests that have been drafted into use to offer speedy diagnoses during the current spate of apparent acts of bioterror weren't designed for the purposes to which they are being put.

Those facts help explain why some of the anthrax test results coming out in recent days have been less than conclusive and -- in the case of the test on a piece of paper sent from Malaysia to a Microsoft Corp. office in Nevada -- apparently wrong.

"The big problem is, we don't have rapid diagnostic capacity for use with human specimens," said Jerome Hauer, former director of New York City's Office of Emergency Management.

When patients grow ill from an infection with Bacillus anthracis, the bacterium that causes anthrax, the microbe multiplies quickly in the body. If the rod-shaped microbes have entered the body through the lungs -- as in the case of Bob Stevens, the Floridian who died of the disease 10 days ago -- they accumulate in the blood and spinal fluid, where they can be seen easily under a microscope. They have a characteristic shape-large rectangles, connected in twos, threes and fours; if a standard microbiological dye is applied, they stain bright purple.

Similarly, if a person has acquired cutaneous anthrax, the variety that affected an NBC employee in New York, even a drop of fluid taken from one of the resulting skin ulcers will reveal the boxcar-like microbes on a microscope slide.

To confirm the diagnosis, these blood, spinal fluid or pus samples are placed on a laboratory dish filled with a nutrient gel, and usually within a day a characteristic gray colony of quickly dividing bacteria becomes visible to the naked eye. Follow-up biochemical and genetic tests, which take about a day, can confirm the obvious diagnosis.

But testing is much trickier in people who have just been exposed, and even harder in samples such as the mysterious powders that have been arriving with alarming frequency in the nation's mailrooms of late.

Some of the letters are described as having white powder and some brown powder. The problem is anthrax spores can come in any color.

Anthrax is a bacterium that thrives in the absence of oxygen. When the bacterium is outside the body, or otherwise exposed to oxygen, it encapsulates itself, forming a spore. These spores can be stored in dried form, later emerging in the active state again once they enter another animal.

Dr. Nick Colovos, an emergency medicine specialist at Allegheny General Hospital who studies bioterrorism issues, said terrorists trying to engender fear might go out of their way to make the spores easily visible.

"A white cloud looks a lot more impressive than brown spores that might just look like dust," he added.

Samuel Watson, director of bioterrorism response programs at the University of Pittsburgh Graduate School of Public Health, said any powder, of whatever color, contained in a suspicious package or envelope probably should be treated carefully.

The nasal swab tests that have been conducted now on about 2,000 Americans who may have been exposed to anthrax-contaminated powders are a crude measure of exposure at best. The idea is to catch a few of the microbes in the nose (if any are there), wipe the swab on a culture dish, and see if any anthrax bugs grow.

If B. anthracis does grow, then clearly the person was exposed to the microbe. Doctors don't know what percentage of the population is walking around with B. anthracis in their noses because no one has ever done a large, baseline study. But they presume the percentage is extremely low, so anyone testing positive has probably had a recent exposure.

If the test is negative, however, it could mean either of two things: There is no B. anthracis in the nose, or none was effectively picked up by the swab. So a negative test doesn't guarantee that the person was not exposed.

Another method that looks for recent exposure to the anthrax bacterium is an antibody test, which looks in the blood for the presence of antibodies directed specifically against B. anthracis. It can take a few weeks after exposure for the body to generate antibodies, so a negative test soon after a suspected exposure doesn't mean no exposure occurred. Moreover, a positive antibody test by itself doesn't mean there's been a recent exposure, because antibodies can last for years in the blood. So antibodies detected in a single test may simply be left over from a brief exposure years ago, one that was successfully fought off.

That means doctors must order a second test a few weeks after the first blood is drawn. An increase in the concentration of B. anthracis antibodies in the blood would indicate the body is building up an antibody army, meaning the exposure was fairly recent.

Even then the results may be difficult to interpret, said David Fleming, deputy director of the Centers for Disease Control in Atlanta. How much of an increase is needed to count as a real increase, he asked, and how much may be due simply to normal variation? No one knows for sure.