Multiple hoaxes, false alarms, premature announcements of contamination, and genuine public fears leading to pressure on emergency rooms have all served to complicate and place heavy strains on investigations here of what is still a small number of confirmed cases of deliberate anthrax contamination.
Over the weekend anthrax was detected in a third state, Nevada, and in a fourth, New Jersey, a suspected case is being investigated. In Florida and New York five and one new exposure cases respectively appear have been detected, all linked to previous cases. To date only one victim has died.
While the Administration is willing to describe the deliberate spreading of anthrax as a form of terrorism no link has been established to September 11th. The Attorney General, Mr John Ashcroft, told a chat show: "We should consider this potential that it is linked \to Osama bin Laden but it is premature at this time to decide whether there is a direct link."
In Nevada an office of a Microsoft subsidiary received a letter from Malaysia containing a returned cheque paid to an agent with some pages of pornographic material which appeared to have been doused with a substance that has since tested positive for anthrax. But the fact that the substance was not in powder form means the likelihood of contaminating anyone was very small, health officials said.
In Edison, New Jersey, a 58-year-old car plant worker is being tested following his developing a rash similar to those associated with the "cutaneous" form of anthrax, the commonest and most treatable form of anthrax, infecting through broken skin.
Ms Erin O'Connor, the assistant to NBC's Tom Brokaw, whose infection was diagnosed on Friday suffered from the cutaneous form, while Mr Robert Stephen, who died 10 days ago, inhaled spores. In rare cases anthrax may also be contracted gastro-intestinally.
American Media Inc. in Boca Raton, Florida, was notified on Saturday by the Centre for Disease Control and Prevention (CDC) that five employees had shown antibodies of anthrax in their blood, according to Mr Gerald McKelvey, a spokesman for American Media. "It means they had an exposure," he said. "It doesn't mean they have anthrax." All are being treated with antibiotics.
A CDC spokesman, however, said the tests were too preliminary to draw conclusions.
Three new cases of exposure to anthrax have been uncovered in New York, Mayor Guiliani said yesterday, stressing the individuals had not developed the disease.
Mr Guiliani said a police officer and two laboratory technicians involved in handling a letter sent to NBC containing anthrax has tested positive for spores of the bacterium.
Initially, authorities believed a September 20th letter sent from Florida, and also addressed to anchor Tom Brokaw, might have been responsible but tested negative. The suspicious letter to New York Times journalist Judith Miller, and which contained a white powdery substance, was also posted in St Petersburg, Forida. Tests on it have proved negative. CBC also faced a similar hoax.
The anonymous NBC letter, which bore no return address, contained an unspecified threat and a brown granular substance, an FBI spokesman said. Most of it was thrown away, but the letter - one of several threatening ones the network received since the attacks - was retained, he said.
Police said it could have been posted from any of 100 collection boxes in Trenton.
Crew and troops on the USS Enterprise in the Gulf have been warned not to open post that does not have a return address that they recognise.
Police report that thousands of people have been queuing in emergency rooms in hospitals to have lesions and rashes checked out while at least two planes have been diverted because of scares involving white powders. In one case the false alarm was caused by the inadvertent spilling of confetti into the plane's ventilation system.