about Epidemiology & the department

Epidemiology academic information

Epidemiology faculty

Epidemilogy resources

sites of interest to Epidemiology professionals

Last Updated

13 Nov 2002

Source: Walnut Creek Journal (California), November 12, 2002.

Study: Low-level anthrax exposure not as dangerous

By SETH BORENSTEIN, Knight Ridder Newspapers

DENVER - Anthrax from a tainted letter sent to Congress last year got into far more people than originally suspected, but it wasn't enough to make them sick, according to a newly released study by the U.S. Naval Medical Research Center.

That means that at low levels of exposure, anthrax may not be as dangerous as was believed during last year's scare.

Because anthrax is so rare, researchers haven't had many studies to tell them what levels are safe. While this study is small and preliminary, it offers hope that the bioweapon isn't as devastating as once feared.

On Oct. 15, 2001, an anthrax-laced letter sent to Sen. Tom Daschle, D-S.D., was opened at his quarters in the Hart Senate Office Building. Subsequent analysis found that it was highly potent and professionally milled. Some 28 people tested positive for exposure and were treated with antibiotics. The letter's sender has not been found.

Now a first-of-its-kind study of immune-system responses to anthrax found that the bacteria did affect people nearby - who originally weren't thought to be exposed - in a small, cell-level way.

The Navy study of 20 people found immune-system reactions in about one-quarter of them. These people were congressional workers who weren't in the high-exposure zone - Daschle's office and the one next door. Some were even in other buildings. The study was released this week at an American Society of Tropical Medicine and Hygiene conference in Denver.

Earlier tests had shown that those people had not developed antibodies to anthrax, but the new tests revealed that their white blood cells had changed to fight the bacteria, said Dr. Denise Doolan of the Naval Medical Research Center.

That means they inhaled anthrax. But the impact of the anthrax was far less than feared.

"Low levels don't cause disease, but low levels do induce immune response," Dr. Daniel Freilich, head of blood substitutions at the Naval Medical Research Center and the study's author, told Knight Ridder on Tuesday.

So the dispersal zone from the biological weapon was far wider than initially recognized, but its bite was less deadly than feared.

None of the people in the study got sick. They didn't show symptoms, and most inhaled such small amounts of anthrax spores that they were not harmed, said Dr. Daniel Freilich of the Navy's Biological Defense Research Directorate.

This research correlates with studies that found small amounts of anthrax spores in congressional office buildings other than Hart. Presumably the spores had traveled through ventilation systems, Freilich said.

These conclusions jibe with research from the 1960s and 1970s on wool workers who showed levels of anthrax bacteria in their bodies but no ill effects, said Dr. Edward Ryan, a top infectious-disease specialist at Massachusetts General Hospital.

The Navy's research also found that victims of the anthrax letter - even those who didn't show symptoms but had immune-system reactions - benefited greatly from getting the anthrax vaccine, Freilich said.