Updated

Hundreds of health officials descended on Atlanta this week for an annual conference on emerging infectious diseases and were warned that terrorists might try to spread deadly germs through the food supply.

Terrorists could try to make the biological attack even more dangerous by taking down critical communications systems, according to experts from the Centers for Disease Control and Prevention.

"The national system was overwhelmed" by the anthrax scare last fall, said Dr. James Hughes, chief of infectious diseases at the Atlanta-based CDC. "Clearly we learned that we were not adequately prepared. This was a small attack."

The conference agenda, usually filled with sessions on obscure diseases and small outbreaks, is dominated this year by information on anthrax and smallpox — considered among the most dangerous terrorist agents.

The anthrax-by-mail attacks killed five people last fall and sickened 13 others. The CDC said earlier this month that a Texas laboratory worker handling anthrax specimens became infected with the bacteria and is recovering.

Hughes said health experts must consider the possibility of genetically altered germs, the release of more than one agent at a time, or transmission through animals and the food supply.

To guard against deadlier attacks, the CDC is distributing $918 million to state and local health departments later this year and next year. The CDC is encouraging them to give priority to upgrading labs and training health workers on how to recognize diseases like anthrax and smallpox.

During and after the anthrax mailings, the CDC was criticized for not communicating clearly to the public about what was myth and what was a real danger. Hughes said some of the millions of dollars to be doled out to prepare for bioterrorism must address communication.

"Clearly, that was something that did not work well during the anthrax attacks," he said. "Our lives have changed. We will be prepared."

The conference also included a refresher course on smallpox, a highly contagious and deadly disease not seen in humans in a generation.

The CDC and a Moscow laboratory hold stocks of the virus, and experts worry that samples could fall into the wrong hands and be converted into a terrorist weapon.

Dr. Stanley Foster of Emory University, who was part of the team that eradicated smallpox, said the United States could react swiftly to a smallpox release, but other countries are extremely vulnerable, with no vaccine or weak public health systems.

Three Johns Hopkins University researchers suggested shutting down all air travel in and out of cities after even one case of smallpox is reported to avoid rapid spread of the disease.

"We could easily have 100 million cases and 20 million deaths," Foster said. "Are we going to be able to prevent it?"