ASHINGTON, March 7 — The widespread use of antibiotics in response to the October bioterrorist attacks spared at least nine people from being infected with inhalation anthrax, the deadliest form of the disease, according to a study released today.

The study, a statistical analysis, tried to forecast how anthrax would have spread in the absence of antibiotics among three affected groups: news media employees in Florida and postal workers in New Jersey and Washington, D.C., all of whom were exposed to letters containing deadly anthrax spores.

The authors of the study calculated that antibiotics, which were given to about 5,000 people in these groups, cut the number of inhalation anthrax cases roughly in half, from an estimated 17 infections to the 8 that the groups incurred.

"This underscores the importance of public health surveillance," said Dr. Ron Brookmeyer, a professor of biostatistics at Johns Hopkins University's Bloomberg School of Public Health who conducted the analysis. "Our rapid detection of outbreaks and distribution of antibiotics prevented disease and possibly saved some lives."

A precise number of saved lives is uncertain because the study is based on statistical modeling that depends on certain assumptions. For instance, when Dr. Brookmeyer changed his assumptions, he calculated that as many as 49 infections were averted by antibiotics.

"This is an estimate, based on the model," said Dr. Donald Berry, a professor of biostatistics at M. D. Anderson Cancer Center in Houston, who was not involved in the study. "It may be right. It may be wrong."

The study did not include every group advised to take antibiotics, like Senate workers or employees at some news organizations in New York. Over all, 5 people died and 13 people became ill in the anthrax attacks, which generated intense anxiety around the nation. In response, public health officials, advised by the federal Centers for Disease Control and Prevention, eventually prescribed antibiotics as a preventive measure to more than 10,000 people, including the 5,000 news media employees and postal workers included in the study.

But the center was roundly criticized for failing to immediately recommend antibiotics to postal workers in Washington, two of whom died. Today, agency officials declined to comment on Dr. Brookmeyer's study, saying they had not reviewed it.

The study, which appears in the current issue of the journal Science, tries to project how anthrax would have spread by relying on data from a 1979 outbreak in Sverdlovsk in the Soviet Union, where a plume of deadly anthrax microbes was accidentally released from a military facility.

The Sverdlovsk incident provided unusually complete data about an anthrax outbreak. But some experts said today that it was not a suitable comparison because the anthrax spores released at Sverdlovsk may not have been as finely processed, or "militarized," as spores sent through the United States mail.

"The Sverdlovsk exposure was very different," said Dr. Brian L. Strom, an epidemiologist who is chairman of a panel of scientific experts for the Institute of Medicine, an independent research group, that recently examined the safety and effectiveness of the anthrax vaccine. "It was an accidental exposure of what probably, in retrospect, looks less likely to be a militarized bacterium."

Dr. Strom said the Sverdlovsk incident had prompted scientists to calculate that a lethal dose for anthrax would be 8,000 to 10,000 spores. But experts said a lethal dose for the anthrax in the October attacks was probably much lower.

Dr. Strom said the study's findings suggested that the extensive use of antibiotics was clearly warranted. "If the model is right, and it saved 9 people's lives, then giving 5,000 people antibiotics" was justified, he said. "We spend a lot of money in order to save a life."

New Bacterial Alert Issued
ATLANTA, March 7 (Reuters) — Citing a need to be vigilant against bioterror attacks, officials at the Centers for Disease Control and Prevention warned health care providers today to be on the alert for outbreaks of tularemia, a potentially fatal bacterial disease.

Tularemia, also known as rabbit fever or deer fly fever, is usually acquired through tick or insect bites or by close contact with infected animals, particularly rabbits and muskrats. It is generally treatable by antibiotics.

The center did not say if the alert was linked to any recent outbreaks.