Public health officials underestimated the health risks when letters containing anthrax (search) spores were handled in five U.S. Postal Service (searchfacilities in 2001, delaying medical help to employees, a report released Thursday concluded.

The report by the Government Accountability Office (search), the investigative arm of Congress, said the Postal Service must revise its guidelines on how it handles future anthrax threats. Two postal workers died from the attack.

"The response to anthrax contamination revealed several lessons, the most important of which is that agencies need to choose a course of action that poses the least risk of harm when considering actions to protect people from uncertain and potentially life-threatening health risks," the report said.

The GAO recommended that the Postal Service clarify the actions it would take under various scenarios, such as when it receives a preliminary report of anthrax contamination or when an employee is diagnosed with anthrax.

Postal Service spokesman Gerry McKiernan said the agency continues to refine its guidelines to be in the best position possible to handle any future anthrax attacks.

The Postal Service relied on public health agencies to assess the health risks to its employees, and the agencies deemed the risks minimal, the GAO said. It was not until the Centers for Disease Control and Prevention confirmed that several postal employees had anthrax that two post offices were closed, in Hamilton, N.J., and the Brentwood location in Washington D.C., the report said.

The GAO's review focused on those two facilities and three others where at least four letters containing anthrax spores were handled in September and October 2001. The contaminated letters resulted in 22 cases of anthrax among the public and postal workers, five of them fatal.

The three other facilities studied were processing and distribution centers in West Palm Beach, Fla., New York City's Morgan location and Wallingford, Conn.

The four letters were mailed to the news media and two U.S. senators, Tom Daschle (searchof South Dakota and Patrick Leahy (searchof Vermont. No one has been arrested in the cases.

Last month, the Postal Service issued its own report that said repeat testing for anthrax was unnecessary in facilities decontaminated following the 2001 anthrax attacks. The Postal Service worked on that report with several federal, health, safety and security agencies.

Continued illness tracking by the Postal Service and federal, state and local health agencies found no evidence of inhalation or cutaneous anthrax in postal employees or customers since November 2001, the Postal Service report said.

The Postal Service is installing anthrax detection equipment in mail handling facilities across the country in hopes of detecting any future attack early and preventing spread of the disease.