FBI and health officials, who say they still have no evidence that the incidents in the three states are linked to the Sept. 11 terrorists or to one another, lead a criminal investigation that is rapidly widening in scope and complexity.
Initially, authorities had focused on a suspicious powder-filled letter sent from St. Petersburg, Fla., to NBC. But that letter - along with a similar one sent to The New York Times - tested negative for anthrax spores.
In Nevada, meanwhile, a letter sent to Microsoft Licensing Inc., a Reno subsidiary of the software giant, was found to be contaminated with anthrax, Gov. Kenny Guinn said yesterday. The letter, which contained a check from Microsoft to a vendor in Malaysia and pornographic pictures, had been tested twice before. Results had been inconclusive or negative.
Thus far, none of the six people who touched the envelope or were nearby when it was opened Friday are known to be infected or showing signs of illness, Guinn said. The letter is being sent to the Centers for Disease Control and Prevention in Atlanta for analysis.
"This is a very, very low risk to public health," Guinn said.
As criminal investigations in New York and Nevada get under way, federal agents in Florida continue piecing together how anthrax was introduced into the headquarters of American Media Inc., the Boca Raton publisher of the National Enquirer and other supermarket tabloids.
Investigators suspect that the deadly pathogen might have arrived in a letter or package because traces of anthrax were found in the company's mailroom and two mailroom workers were found to have been exposed to the bacteria.
The only other place anthrax was located in the building was on the computer keyboard of Robert Stevens, a photo editor who died Oct. 5 of inhaled anthrax, the most serious form of the disease.
Yesterday, the tabloid company learned from the CDC that five more employees had been exposed to anthrax, said spokesman Gerald McKelvey.
More than 1,000 employees and visitors to the American Media building have been given nasal tests for anthrax in the past week.
As a precautionary measure, CDC officials are also testing about 20 mail sorters who work at three post offices that serve American Media
In New York, officials are closely watching a second NBC employee who is exhibiting a fever, rash and other symptoms of anthrax. The employee, who has not been identified, is being treated with antibiotics while officials await test results.
About 200 NBC employees, including Brokaw, are being tested for exposure to anthrax since Brokaw's aide, Erin M. O'Connor, was found Friday to have developed the cutaneous, or skin, anthrax, a less serious form of the disease.
O'Connor developed a rash on her chest several weeks ago, health officials said. When it worsened, she consulted a doctor Oct. 1, who prescribed the antibiotic Cipro. Health officials learned Friday from skin biopsy results that she had anthrax.
O'Connor was one of several NBC employees thought to have handled the tainted letter, which contained a sand-like substance.
There was some confusion about why investigators in New York only learned about the Trenton letter yesterday, while the St. Petersburg letter sent to NBC Studios was turned over to the FBI on Sept. 26, the day after it was received.
NBC Chairman Bob Wright explained at a news conference that the Trenton letter was accidentally filed in a folder where the company keeps other threatening letters. Wright added that it was not unusual for employees to get such letters.