But in Halifax, Canada, tests found no anthrax. As reports pour in from around the world, national leaders try to soothe jangled nerves. Jean Chretien said, "It is a period of uncertainty and as Roosevelt said, there is nothing worse than fear of fear."
On the London Stock Exchange, 12 workers were hospitalized. Elsewhere in England, hundreds of postal workers were evacuated.
In Japan, staff at the US Consulate in Osaka were treated with antibiotics because of a concern about a suspicious package.
In Kenya and Argentina, tests found anthrax spores in letters mailed from the United States. So far the only place where people have contracted the disease is the United States.
Dr. Paul Salkovskis, said, "What has happened over the last few weeks has demonstrated to people that they might be in danger almost anywhere."
Dr. Salkovskis is an expert on anxiety disorders. He believes the combination of attacks, the destruction of symbols of stability in the world's most powerful nation, and now anthrax is creating worldwide anxiety.
"The whole society is experiencing the kind of thing that happens to people when they have post-traumatic stress disorder. Their basic beliefs about their security, their safety, are violated and they simply do not know what is going to happen next," Dr. Salkovskis said.
Governments are working to calm fears. They are increasing safety measures at post offices, using X-ray machines for all foreign mail, and Israel, the target of Iraq's Scud missile attacks a decade ago, now hands out gas masks and facts.
Yair Sharon, from Tel Aviv University, said, "Bioterrorism, even though it's very threatening, causes very few casualties, and I hope it remains like that."
With most of the anthrax cases turning up as false alarms, governments are raising penalties for people who commit hoaxes. The goal is to reduce false threats at a time when the world faces too many real ones.
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