An anxious physician is on the phone, seeking advice from the city's infectious disease director about giving the antibiotic Cipro to a sick Federal Express worker who doesn't even have anthrax symptoms.

The reassuring words of the director, Dr. Pamela Diaz, are tinged with uncertainty.

"Everybody has to be a little more alert than usual without being over the edge," Diaz tells the doctor.

There have been no confirmed reports of anthrax or anthrax exposures in Chicago or most other major U.S. cities. But since Sept. 11, bioterrorism is the only topic of discussion for public health administrators like Diaz, who's been working 18-hour days, seven days a week.

A voicemail message this past week from the federal Centers for Disease Control and Prevention invited Diaz to discuss local preparedness at an upcoming CDC meeting. Later, a colleague discussed using Census data to guide distribution of medicine if widespread bioterrorism hits Chicago.

Diaz agreed to the Census tracking discussion during what is now a daily and sometimes twice-daily meeting with staff epidemiologists on the latest developments.

But she said the CDC invitation was likely out of the question. The Oct. 30 meeting would require being away around Halloween, a day that even in the best of times brings in horror hoaxes and pranks. And Diaz figures she ought to stick around.

Diaz works in Chicago's Department of Public Health, which exists to protect the city's nearly 3 million people from disease through education, disease tracking and prevention. In normal times, that means things like providing vaccinations, urging condom use to prevent venereal disease and monitoring flu outbreaks.

In these times, the agency's focus is on anthrax, and Diaz is in charge.

Diaz says her department is continually brainstorming and updating its plan while watching anthrax events unfold in places like Washington, Florida and New York.

"We're all learning as we go because anthrax through the mail is not something that we've had a lot of experience with," she said.

While Chicago just put a bioterrorism preparedness plan in writing a year ago, Diaz said the issue has been on the department's radar for several years, prompted by events including the 1993 World Trade Center bombing, the 1995 sarin gas attack in Tokyo and the Oklahoma City bombing.

For security reasons, Diaz won't reveal details of the city's preparedness plan. She said it includes elements as simple as making sure department staff members have all-hours phone numbers for key city and state officials, and as complex as mapping out how best to get medicine quickly to all areas of Chicago.

An agency hot line receives dozens of calls daily from people who think they came in contact with suspicious powder and from doctors seeking advice on how to deal with them.

At a staff meeting this past week, epidemiologist Usha Samala told of receiving 20 phone calls the previous day, most from people concerned about handling letters that had been routed through the Washington post office.

"Right now, there's not any recommendation to be concerned" about such mail posing a health threat, Diaz told the group. If there were, there'd be scores of cutaneous anthrax cases around the country, added Dr. William Paul, the city's deputy public health commissioner.

There were no easy answers for the doctor who gave Cipro to the sick Federal Express worker without anthrax symptoms. The same day he called, Diaz' department prepared a health alert for the city's 38 hospitals warning against prescribing unnecessary antibiotics.

But Diaz, who has never treated an anthrax patient and knows that most other doctors haven't either, treads cautiously. She takes the patient's phone number to get his work history and determine if he had contact with any suspicious packages.

"Doctors don't know if there really is a problem in Chicago or not," she explained later.