Los Angeles Times

WASHINGTON Anthrax infections in two East Coast women with no known links to contaminated letters are forcing government officials to rethink basic assumptions about how easily the disease may infect people and how widely it may have spread through the mail.

Government investigators said yesterday they could not explain how the deadly bacteria infected a New Jersey bookkeeper, who is recovering from skin anthrax, and a 61-year-old New York hospital supply clerk who is critically ill with the more dangerous inhaled form of the disease.

The women are the nation"s 15th and 16th confirmed anthrax victims, but neither appear to have received suspicious mail or spent time at a contaminated postal facility.

"Did they get infected from a piece of mail that went to their home?" asked Dr. Anthony Fauci, director at the National Institute of Allergy and Infectious Diseases. "That is being intensively investigated right now."

Rep. Rush D. Holt (D-N.J.), whose Capitol Hill office tested positive for anthrax traces, said the newest cases raise the level of concern for everyone.

"Up until now, it was easy for most people to say: Well, I don"t work in a post office, and I"m not a public figure, so therefore I don"t have to worry," " Holt said.

The greatest concern involves the New York woman, who asked officials not to disclose her name. Until now, health officials have assumed that an inhalation anthrax infection could only be acquired by a person who breathed thousands of anthrax spores.

Health experts also instructed anyone who had spent at least one hour in the Manhattan hospital since Oct. 11 an estimated 5,500 employees, patients and visitors to start taking antibiotics.

That, they believed, would be impossible unless a person came into direct contact with a letter containing anthrax. So-called cross-contamination a letter simply picking up spores by moving through the postal system would not be enough, officials have thought.

If the woman received such a letter, that would be a significant new front in the anthrax problem. To date, the only confirmed anthrax-laced letters have been to media organizations and the office of Senate Majority Leader Tom Daschle (D-S.D.).

If she did not receive a letter, however, then officials must confront the possibility that anthrax is more infectious than they had believed.

"It"s not what we know or don"t know that gets us in trouble. It"s what we know that turns out to be wrong," said John D. Clements, chairman of microbiology and immunology at the Tulane University School of Medicine. "This could be a classic example of that."

Government officials have relied on research conducted by the Department of Defense in the 1980s suggesting that inhaling 8,000 anthrax spores can cause lethal infections in monkeys. Other studies by the World Health Organization place the figure at 50,000 spores among animal hide workers in Third World countries. A 1999 paper in the Journal of the American Medical Assn. suggests that inhaling 2,500 spores or more would cause an inhalation infection.

Dr. Bradley Perkins, an anthrax expert at the Centers for Disease Control and Prevention in Atlanta, said Tuesday that no one can accurately pinpoint the number of spores needed to cause infection in humans.

"We know at the two extremes," he said, noting that a large number more than 5,000, for example clearly poses a significant human danger. Fewer than 10 pose very little risk.

"It"s what"s in between" that is an issue, he said. "We don"t have either research experience or even clinical experience or epidemiological experience to be able to give a definitive answer on that."