FBI Director Robert Mueller announced a reward of up to $1 million for information leading to the arrest and conviction of those responsible for sending anthrax-laden mail.
"The mailing of anthrax is a terrorist act," Mueller said, "and we are pursing it as a terrorist act."
The CBS employee was infected with cutaneous anthrax -- the type contracted through the skin -- which is less deadly. An aide to NBC News anchor Tom Brokaw in New York also has been infected with cutaneous anthrax.
New York Mayor Rudolph Giuliani said the woman at CBS worked with the mail and added, "She is recovering, if not recovered completely" after receiving antibiotics.
Homeland Security Director Tom Ridge told a news conference Thursday that "thousands and thousands and thousands" of people had been tested for anthrax around the country but only a handful had tested positive for infection.
The five confirmed infections include the CBS and NBC employees, a 7-month-old baby of an ABC News employee, Stephanie Dailey, an employee of tabloid publisher American Media Inc. in Boca Raton, Fla., and Robert Stevens, 63, the AMI photo editor who died of inhaled anthrax infection on Oct. 5.
AMI mailroom worker Ernesto Blanco, 73, was listed as a "probable" case of anthrax but state health spokesman Tim O'Connor said he was improving.
A sixth possible case involving a Trenton, N.J., postal working was being reported. Greg Niederman, a spokesman for the post office told United Press International that there was no official word of an anthrax case among the workers there. He noted that a local radio station was reporting that there was a case, but, as of noon, no confirmation of such an infection had been received. He did know that preliminary tests were negative.
Also, according to the Centers for Disease Control, all tests on a letter sent to a Microsoft office in Reno, Nev., were negative for anthrax.
Ridge said more than 3,000 nasal swabs had been taken to test for anthrax exposure and all of those people tested were offered antibiotics.
Thirty-one people, including Capitol police and staffers of Senate Majority Leader Tom Daschle, D-S.D., tested positive for exposure after an anthrax-laced letter was delivered to Daschle's office on Monday.
The U.S. House and offices were closed Thursday through Monday for a security sweep for anthrax spores. So far the only spores found have been in Daschle's office in the Senate's Hart building as well as in the mailroom there.
U.S. Surgeon General David Satcher said there are plenty of antibiotics to treat all anthrax exposures and that the nation's stockpile, which had included enough medication to treat 2 million people for the 60-day course recommended for anthrax, has now been expanded to 12 million doses.
The Department of Health and Human Services also flagged penicillin and doxicycline as anthrax treatments, along with Cipro, which was approved for anthrax in May and is the preferred treatment if health officials are unsure of the bacterial strain. Cipro has been shown to be less susceptible to problems of antibiotic resistance, but for strains of anthrax found to be responsive to antibiotics, penicillin and doxycycline can be used.
Attorney General John Ashcroft said federal law enforcement is working closely with federal and state health agencies to find those responsible for the anthrax letters. He said the actual perpetrators and anyone involved in an anthrax hoax "will pay a serious price because we intend to prosecute these offenses to the fullest extent of the law."
Ashcroft called the anthrax cases a "grotesque transgression of the public trust" and the "destructive act of cowards."
The CDC has confirmed that its analysis showed no difference between the strains of anthrax found in New York and Florida and called the grade of anthrax found in Washington "run of the mill." All strains have been found to be treatable with antibiotics.
Retesting of 400 other AMI employees is under way, and results are expected by the end of the week. Blood tests have shown four of those employees may have had exposure to anthrax at some point.
An 8-year-old boy, the son of an employee, was tested because of a suspicious rash, but results Wednesday were negative.
American Media President David Pecker said the sales of the company's supermarket tabloids is down 10 percent but he expects them to bounce back.
A 17-year-old student at Flagler Palm Coast High School in central Florida has been charged with carrying out an anthrax hoax by pouring a white substance on a classroom chair. It turned out to be a headache powder.
James Smith, charged with a second-degree felony, is believed to be the first person arrested in the state for a hoax involving weapons of mass destruction. He said he just wanted to get out of a day of school.
Prosecutors said age isn't a factor in the case. If he is prosecuted as an adult he could be sentenced to 15 years in prison.
Notable deaths of 2014 [PHOTOS]