Anthrax Exposure at the Brentwood Mail Center Examined

Jan. 8, 2002
The CDC examines the trail of anthrax contamination left by a letter processed at the Brentwood Mail Processing Center in Washington, D.C.

The Dec. 21 edition of MMWR Weekly includes an evaluation of B. anthracis contamination inside the Brentwood Mail Processing and Distribution Center in the District of Columbia that occurred in October 2001.

From Oct. 19 through the 21 of last year, four postal workers at the Brentwood facility were hospitalized with inhalational anthrax and two of the workers died. The building, which was closed on Oct. 21, was believed to have been contaminated by a letter containing B. anthracis spores sent to the Hart Senate Office Building (HSOB) that had passed through the postal facility on Oct. 12. A second contaminated letter addressed to another U.S. senator that was processed through the same mail sorter and sort run as the first letter was discovered on Nov. 17.

The report in MMWR Weekly describes the results of the Centers for Disease Control and Prevention''s (CDC) evaluation of B. anthracis in the facility. CDC''s investigation showed widespread contamination of the facility and suggests that wipe samples and high efficiency particulate air (HEPA) vacuum samples complement each other in assessing contamination.

According to the report, a U.S. Postal Service investigation indicated that, on late Oct. 11 or early Oct. 12, the letter sent to one U.S. senator entered the building in a mailbag through a loading dock near the Postal Vehicle Transportation Office. The report then follows the trail of the letter through the mail distribution center.

On Oct. 18, before recognition of inhalational anthrax cases among workers at the mail center, a Postal Service contractor collected 29 swab samples from the mail sorting area of the Brentwood facility. On Oct. 20, CDC initiated an investigation of the Brentwood facility. As part of this investigation, CDC extended the evaluation of B. anthracis contamination in the Brentwood facility.

Sampling for B. anthracis spores began on Oct. 24 using three techniques: surface wipe sampling, surface vacuum sampling, and air sampling. The evaluation focused on the path of the HSOB letter through the facility and the work locations of the known anthrax patients.

To evaluate the extent of B. anthracis contamination, additional samples were collected throughout the facility, including the administrative areas on the second level and the customer service area at the front of the building. Wipe samples were submitted to CDC for culture and analysis.

According to the report, some eight out of 114 surface wipe samples (7 percent) - taken from such surfaces as table or desk tops, sorting machines, sorting bins, control consoles of sorting machines, and ventilation ducts - tested positive for isolates of B. anthracis.

Of 39 vacuum dust samples taken, B. anthracis was isolated in 27 (69 percent), with all eight samples collected in the government mail area testing positive, although no wipe samples collected in this area were positive.

Twelve air samples for airborne B. anthracis spores were collected 12 days after the contaminated letters were processed, which was four days after the building was closed and the ventilation system was turned off. The ventilation system was not operating during the sampling period. All air samples were negative for B. anthracis, indicating that no airborne spores were detectable during the sampling period.

Environmental sampling results in this investigation indicated widespread contamination from the letters processed for delivery to the offices of two U.S. senators. Only the second level administrative area and the customer service area appeared to be free of spores by all testing methods.

Researchers suggest that the results of the environmental sampling at the Brentwood facility might be used to assess the extent of contamination and are consistent with the aerosolization indicated by the cases of inhalational anthrax. They also should help guide cleanup efforts and can serve as a baseline for follow-up environmental assessments after the building has been cleaned. In addition, these results suggest that vacuum sampling is a useful complement to wipe surface samples, particularly when widespread contamination is suspected.

Current CDC guidelines for collecting environmental samples are available at

by Sandy Smith ([email protected])

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