Experts say the rare disease can be used as a biological warfare agent. But a senior government health official sought to allay any such fears in this case.

"If this was a massive exposure, there should be lots of people sick. We are not finding that," Dr. Scott Lillibridge, U.S. Health and Human Services Secretary Tommy Thompson's special assistant for bioterrorism, told members of Congress in Washington.

In Boca Raton, FBI investigators in protective gear scoured the sealed-off American Media Inc. offices for clues to the source of the anthrax contamination, which killed photo editor Robert Stevens on Friday. The company publishes The National Enquirer and other sex-and-scandal tabloids.

On Sunday, mailroom employee Ernesto Blanco, was found to have been exposed to the disease, and traces of anthrax were also found on a computer keyboard in the AMI building.

Florida health officials said they had still not determined if the anthrax strain was natural or engineered - a fact that could help decide if the contamination was a criminal act. Experts appear to have concluded that the cases point to something other than a natural exposure but local FBI officials yesterday gave no indication of their findings.

CDC FIELDS ANTHRAX CALLS

The Florida contamination has fueled fears in a public already on edge over last month's hijack attacks.

The Centers for Disease Control and Prevention said yesterday it was fielding large numbers of calls from Americans worried about anthrax.

"We're getting a lot of the same questions over and over again about whether the anthrax is contagious and whether they should buy antibiotics or a gas mask," CDC spokeswoman Lisa Swenarski said.

Swenarski said the CDC was advising the public to remain calm and not horde antibiotics or buy gas masks.

Florida state emergency management officials said they received 19 reports this week of suspicious substances being found, most of which were quickly determined to be harmless.

In Miami, the county fire-rescue department said it received about 100 calls this week and Yesterday from people reporting suspicious substances. None turned out to be hazardous.

There were also scares in Washington, Virginia, Kentucky and Montreal, Canada, this week. Florida officials asked the public to be "alert but smart."

And while scientists analyzed tests taken from several hundred people on Monday and Tuesday, pharmacists in the Boca Raton area reported far higher-than-usual sales of Cipro, an antibiotic made by Bayer AG used to treat anthrax.

Joshua Lubitz, a pharmacist at an Eckerd drugstore about three miles (five km) from the AMI building, said: "We have probably seen 10 times the volume we normally do in a week in the past couple of days."

Lubitz said that having talked to pharmacist colleagues the phenomenon was "pretty rampant in the Boca Raton area."

In Washington, the U.S. State Department said it had told all U.S. Embassies abroad to stock up on ciprofloxacin in case of anthrax attacks.

BUYING TABLOID NO RISK

AMI Chairman David Pecker scotched rumors that buying a copy of a tabloid risked coming into contact with anthrax. The Boca Raton office housed editorial and management but printing and shipping was handled by five other plants, none of them in Florida, he said.

Editorial operations had been shifted to other offices so publication schedules had not been disrupted, he added.