Citing the terrorist attacks, the agency's weekly health bulletin urged doctors to be alert for unusual outbreaks among people who have attended the same public event. It said doctors should also watch for unusual age distribution in diseases, such as a chicken pox-like illness in adults.

The CDC also asked state health departments to come up with plans to teach health care providers how to recognize unusual diseases that might be cases of bioterrorism.

There is no evidence of any specific threat from agents other than anthrax, said Dr. Julie Gerberding, acting deputy director of CDC's National Center for Infectious Disease.

Still, the article was a rare immediate warning in the CDC's Morbidity and Mortality Weekly Report, which typically includes detailed explanations of disease outbreaks that happened months ago.

The report said state health officials should remain on 24-hour alert for reports of intentional release of biological agents and to report any outbreaks immediately to federal officials.

In a list of biological agents ``of highest concern,'' the CDC included plague, additional cases of anthrax and a rare bacteria called tularemia that humans can contract from the carcasses of dead animals.

Bill Kvasnicka, a professor of microbiology at the University of Nevada in Reno, said the threat of anthrax pales in comparison to the potential danger of other virulent diseases.

``There are other agents that would lend themselves to more devastation and probably would be easier to disperse,'' he said. ``Of course, in humans, plague and other viral infections where there are not treatments would be devastating. Smallpox would also be devastating. People not only become exposed to smallpox, they also spread the virus.''

The CDC said state health departments should have plans to safely store and transfer any specimens that need to be analyzed. It also asked hospitals to ensure they have fast ways to contact infectious-disease specialists and authorities in case of bioterrorism.

CDC's recommendations Thursday were in addition to a warning the agency issued shortly after the terror attacks, asking health care workers to be alert for unusual diseases.

CDC listed the following biological agents as ``of highest concern,'' asking doctors to be alert for their symptoms:

_Pneumonic plague, whose symptoms include fever, chest pain and a cough that produces a saliva-mucous mixture or blood.

_Botulism or food poisoning, which can produce drooping eyelids, a weakened jaw, blurred vision and paralysis of muscles around the lungs.

_Smallpox, which produces two to four days of fever and muscle pain before a rash and lesions appear.

_Tularemia, whose symptoms include a fever for three to five days followed by difficulty breathing, often caused by liquid in the chest cavity.

_Hemorrhagic fever, which can be caused by viruses like Ebola and produces a wide range of symptoms, including vomiting, rash, muscle pain and massive internal bleeding.

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On the Net:

CDC bioterrorism site: http://www.bt.cdc.gov

Johns Hopkins Center for Civilian Biodefense: http://www.hopkins-biodefense.org

U.S. Armyinfectious disease site: http://www.usamriid.army.mil/education/bluebook.html