Health experts say the Florida anthrax cases traced to the newsroom of a supermarket tabloid do not fit the classic bioterrorism scenario and the public should not especially fear for its safety while the FBI continues its investigation.
Among the major questions to be answered: Where did it come from? How was it spread? And, why has only one person died?
"There are things about this case that I find rather strange," said Donald A. Henderson, a biodefense expert at Johns Hopkins University in Baltimore. "If you put them all together, they don't add up."
Anthrax is one of a handful of microbes turned into biological weapons designed to infect and kill large populations. A treaty signed by 143 nations bans their use. But U.S. officials have long feared that extremists might grow a large batch and release anthrax spores on unsuspecting, innocent people -- fears that have become acute since the Sept. 11 terrorist attacks.
In Florida, Bob Stevens, 63, died Friday of inhaled anthrax. It was the first confirmed case in the United States since 1976. The bacterium also has been found in the nasal passages of one of Stevens' co-workers at The Sun newspaper. That man is being treated at an undisclosed Miami-area hospital.
However, experts said the bacterium's presence in the man's nose does not necessarily mean he is suffering from the inhaled form of the disease, in which tiny spores flourish deep in lung tissue.
Anthrax spores also were found on Stevens' computer keyboard, a state health official said. The FBI has sealed off the office building and is expected to begin combing it for clues.
National health experts said the FBI investigation was "appropriate," but doesn't necessarily mean it was the work of terrorists.
"If you had a large release (of anthrax spores), you wouldn't see just one case," said Bruce Clements, associate director of St. Louis University's Center for the Study of Bioterrorism and Emerging Infections. "We would see quite a few cases."
"Anthrax is so persistent," he said. "If somebody let aerosolized anthrax loose in air system of that building, it will still be there."
All 300 employees who work in the building housing the Sun tabloid were asked to come to a clinic so they could be tested for the bacteria. Centers for Disease Control and Prevention officials said nasal swabs would be taken, and antibiotics provided to combat the disease in its early stages.
Anthrax symptoms -- which initially resemble the flu -- usually take up to a week to appear, but may not develop for 60 days.
In inhaled anthrax, the body quickly produces toxins as a result of infection that antibiotics typically cannot overcome.
Health officials said they have not heard anything yet to suggest the second newsroom worker has the inhaled version. Nor do the spores suggest they were biologically manipulated.
"It looks like garden-variety anthrax," said Henderson of Johns Hopkins. "We should know more in a few days when the tests are concluded."
The CDC has identified two antibiotics -- Cipro and doxycycline -- to treat anthrax.
Health experts said "it would be prudent" to treat workers in the Sun building, as well as any visitors, messengers, delivery people and service workers who went there in the past two months. Family and friends who were not physically there would not need treatment because anthrax cannot be passed from person to person.
"You want to treat people before they show symptoms," Clements said.
In the past century, most people who have contracted inhaled anthrax worked in mills and were processing goat hides that carried the spores.
A slower, non-inhaled infection can be contracted by eating anthrax-infected meat -- almost eliminated now with modern food safety standards.
Anthrax spores live in the soil in areas where livestock graze. Humans can develop slower, treatable anthrax infections in the skin if soil-borne spores contaminate a cut or abrasion.
Spores remain viable in the soil for decades. In 1942, Winston Churchill ordered germ warfare tests on Gruinard Island off the coast of Scotland. The 520-acre island was contaminated and off-limits until a massive government cleanup began in 1986.
Workers removed tons of topsoil, then soaked the remaining ground in seawater spiked with large amounts of formaldehyde.