As a weapon of mass destruction, anthrax has so far proved to be less than effective - with just one fatality and a handful of illnesses resulting from the spate of recent cases. But as a form of psychological warfare, it's having a profound impact.
Discoveries of additional cases - including a letter containing anthrax sent to Senate majority leader Tom Daschle's office, and the 7-month-old son of an ABC News producer testing positive for exposure - have undoubtedly added a new level of gravity to the situation, which the government now officially refers to as terrorism.
Yet, with these new cases have also come literally hundreds of hoaxes and false alarms, demonstrating that terrorism doesn't have to involve widespread loss of life to be effective. While not nearly as devastating as the Sept. 11 attacks, the anthrax cases have been arguably more powerful in getting under Americans' skin, creating a sense of fear that has disrupted daily routines.
Newsrooms have been evacuated after receiving letters laced with talcum powder, and jittery Americans across the nation have called authorities to test everything from beach sand to confetti.
Congress, seems especially on edge. Eleven offices near Senator Daschle's office have been shut down, and all mail to the House and Senate has been suspended. Even before the letter to Daschle was discovered, Sen. Dianne Feinstein (D) of California was already instructing everyone on her staff to wear masks and gloves while opening mail, and Senate minority leader Trent Lott has called for bulletproof glass to protect the Senate floor.
So far, public-health officials have managed to respond to each case relatively quickly. But experts warn they may be increasingly hindered by the flood of calls and other incidents that continue to demand their attention.
"This is the kind of thing that terrorists want - they want to put sand in the gears," says Rep. Christopher Shays (R) of Connecticut. "They don't always need to do something dramatic. But this forces us to spend a lot of time and attention on something that's fairly easy to do. You know, just get some anthrax and contaminate a letter and send it to whomever. Everybody becomes a potential target, at random."
Indeed, it's this sense of randomness, and an innate fear of the unknown, that has managed to deeply unsettle so many Americans.
"What makes [anthrax] an effective terror weapon is that the psychological impact is really profound," says Jessica Stern, a lecturer on terrorism at the Kennedy School of Government at Harvard University in Cambridge, Mass. "People have a natural, age-old aversion to poison. And so I think it's completely understandable and natural that people respond this way."
Ms. Stern says psychologists have identified 18 variables associated with biological weapons that tend to create a disproportionate sense of threat. These include: invisibility, a lack of scientific understanding of the substance, the possibility of long-term effects, and not knowing immediately when you've been affected.
And so, while the chances that the average American will be exposed to anthrax are still "extremely unlikely," Stern says, "the whole country is feeling jittery - even though, mostly, we're talking about talcum powder."
Powder is by far the most effective way to distribute anthrax, according to experts, although there can be wide variation in what that powder looks like.
"You will typically see it in some sort of powder or dried-down form," says Calvin Chue, a research scientist at the Center for Civilian Biodefense Studies at Johns Hopkins University in Baltimore. "But whether it's white or clear or brown and smelly, depends on how good the group has been in trying to purify it."
This variation has made any and all granular substances suddenly seem like potential weapons to many Americans.
Last weekend, a United Airlines flight was grounded for three hours after a passenger opened a gift card that contained confetti. The man was escorted off the plane, stripped of his clothing, and sprayed with detergent.
A Denver post office was evacuated last week after an envelope broke open, spilling white powder. Four workers were decontaminated, and the substance was rushed to a lab - where it was found to be vanilla-pudding mix.
On a more serious note, the nation has become more vulnerable to hoaxes. On Monday, Planned Parenthood reported that 90 of its clinics and offices in 13 states had received threatening letters containing an unidentified powdery substance. Initial tests have come back negative for anthrax, although more are being conducted.
Anthrax hoaxes are nothing new, experts point out. "In the years preceding this, there were literally hundreds of hoaxes involving anthrax across the country," says Amy Smithson, director of the Chemical and Biological Weapons Nonproliferation Project at the Henry L. Stimson Center in Washington. About one-third of these hoaxes came from antiabortion groups.
But perhaps never before have they been so disruptive. During a recent 24-hour period, New York City officials responded to no fewer than 100 calls. In the worst-case scenario, says Stern, hoaxes are not only "extremely expensive to respond to, but they could actually result in lost lives."
Many are calling on law enforcement to crack down on hoaxes.
Yesterday, on ABC's "Good Morning America," New York's Mayor Rudolph Giuliani said the FBI had arrested two people who had sent hoax anthrax letters, and that they would be prosecuted fully. "People doing that now really are creating enormous problems for the police and the FBI," he said.
Emergency responders will also have to develop better procedures for weeding out false alarms, say experts, although they warn that this could take some time.
"We're in a period of adjustment," says Stern. "What is happening in the United States is that we're having to learn to live with a level of risk that we're not accustomed to. And it's going to take a while before we figure out how to deal with this."