about Epidemiology & the department

Epidemiology academic information

Epidemiology faculty

Epidemilogy resources

sites of interest to Epidemiology professionals

Last Updated

11 Dec 2002

Source: Reuters, December 10, 2002.

Office Activity Stirs Up Weeks-Old Anthrax Spores

By Merritt McKinney

NEW YORK (Reuters Health) - The anthrax mailed to a Senate office last fall was able to become airborne again even after it settled in the office, US government scientists reported Tuesday.

The fact that ordinary movement in the office was enough to send anthrax back into the air provides evidence that the spores were altered to make them more dangerous, according to Dr. Christopher P. Weis of the US Environmental Protection Agency National Enforcement Investigations Center in Denver, Colorado.

In an interview with Reuters Health, Weis said that scientists thought that once the anthrax-laden envelope was opened, the spores would settle in the office and would be unlikely to become airborne again. But when Weis and his colleagues simulated normal workplace activities -- such as paper handling, walking around the office and mail sorting -- several weeks after the envelope arrived, the spores easily became airborne, according to a report in the December 11th issue of The Journal of the American Medical Association.

Measurements of anthrax in the air of the office were substantially higher after researchers simulated everyday office activity than when the office was more still. And more than 80% of the airborne anthrax spores were of a size that could easily be breathed into the lungs.

The evidence that the anthrax spores were capable of becoming airborne again offers proof that "the natural behavior of these materials was altered," Weis said. He explained that the particles were much smaller than naturally occurring anthrax spores. Weis and his colleagues expected that the anthrax spores "would clump together" and settle on various surfaces in the office. These clumps of small anthrax spores would be unlikely to become airborne again, he said.

The anthrax in the envelope, however, was apparently altered in some way to make it more easily airborne, the EPA scientist said. The experience in the Senate office shows that scientists may not be able to predict how future attacks with disease-causing substances such as anthrax will play out, Weis said. The results also underscore the importance of protecting workers involved in decontaminating anthrax-exposed areas, he and his colleagues conclude.

Weis added that the lessons obtained by studying the anthrax in the Senate office, including the revelation that anthrax was more likely to become airborne than expected, demonstrate the importance of having scientific teams come in to conduct an analysis after such an episode.

"There is a need for science and a discussion of science to help guide health officials and protect public health," Weis said. He said that the "incredible collaborations among federal scientists" made the work a success.

Besides Weis, the effort was led by Anthony J. Intrepido of the US Army Center for Health Promotion and Preventive Medicine in Aberdeen Proving Ground, Maryland. The team also included researchers from the US Public Health Service in Denver, the US EPA in Cleveland, Ohio, and the Naval Medical Research Center in Silver Spring, Maryland.

SOURCE: The Journal of the American Medical Association 2002;288:2853-2858.

ABSTRACT: JAMA. 2002;288:2853-2858

Secondary Aerosolization of Viable Bacillus anthracis Spores in a Contaminated US Senate Office

Christopher P. Weis, PhD; Anthony J. Intrepido, MS, CIH; Aubrey K. Miller, MD, MPH; Patricia G. Cowin, MS, CIH; Mark A. Durno, BS; Joan S. Gebhardt, PhD; Robert Bull, PhD

Context: Bioterrorist attacks involving letters and mail-handling systems in Washington, DC, resulted in Bacillus anthracis (anthrax) spore contamination in the Hart Senate Office Building and other facilities in the US Capitol's vicinity.

Objective: To provide information about the nature and extent of indoor secondary aerosolization of B anthracis spores.

Design: Stationary and personal air samples, surface dust, and swab samples were collected under semiquiescent (minimal activities) and then simulated active office conditions to estimate secondary aerosolization of B anthracis spores. Nominal size characteristics, airborne concentrations, and surface contamination of B anthracis particles (colony-forming units) were evaluated.

Results: Viable B anthracis spores reaerosolized under semiquiescent conditions, with a marked increase in reaerosolization during simulated active office conditions. Increases were observed for B anthracis collected on open sheep blood agar plates (P<.001) and personal air monitors (P = .01) during active office conditions. More than 80% of the B anthracis particles collected on stationary monitors were within an alveolar respirable size range of 0.95 to 3.5 micrometers (microns).

Conclusions: Bacillus anthracis spores used in a recent terrorist incident reaerosolized under common office activities. These findings have important implications for appropriate respiratory protection, remediation, and reoccupancy of contaminated office environments.