Filed at 5:07 p.m. ET

ATLANTA (AP) -- Some people who may have been exposed to anthrax are not taking the full 60-day regimen of antibiotics they were prescribed, putting them at risk for infection, federal health officials said Thursday.

About 5,000 people have been prescribed the 60-day regimen, with thousands more prescribed a shorter regimen.

People have stopped taking the drugs prematurely because they see no signs of illness, officials at the Centers for Disease Control and Prevention said. Others stop because of unpleasant side effects such as nausea or because prescriptions run out.

Taking the drugs for the full two months is the only way to ensure the anthrax bacteria do not develop into a full-blown case of the potentially fatal disease, officials said.

``They still are at risk of developing anthrax if they do not complete their antibiotic therapy,'' said Dr. Julie Gerberding of the CDC. ``This is such a serious disease that it makes sense to err on the side of completing the full 60 days.''

The CDC also published an expanded list of people who ought to be taking antibiotics, like doxycycline and Cipro.

People who visited the Boca Raton, Fla., offices of a tabloid publisher as far back as August are being urged to go on the full 60-day regimen of antibiotics. Other groups include:

--Employees on the second and third floors of the south section of the Morgan Central Postal Facility in Manhattan between Oct. 9 and Oct. 26. Five machines there have tested positive for anthrax.

--Workers and visitors who were in the postal service's Route 130 Processing and Distribution Center in Hamilton, N.J., between Sept. 18 and Oct. 18. Two employees there contracted inhalation anthrax.

--People who were on the fifth and sixth floors of the southeast wing of the Hart Senate Office Building in Washington between 9 a.m. and 7 p.m. Oct. 15. An anthrax-filled letter to Senate Majority Leader Tom Daschle was opened there that day.

--Employees and visitors to the nonpublic mailroom of the postal service's Brentwood facility in Washington between Oct. 12 and Oct. 21. Two postal workers there died of inhalation anthrax.

--Mailroom employees and visitors who were at the State Department's Annex 32 mailroom in Sterling, Va., between Oct. 12 and Oct. 22. A mail handler there contracted inhalation anthrax.

The CDC also Thursday said the drug amoxicillin is an acceptable alternative for children and pregnant women who may have been exposed to anthrax. Cipro and doxycycline can cause significant side effects in children and are not readily available in liquid form.

The only confirmed child case of anthrax is a skin case in the 7-month-old son of an ABC News producer in New York.

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On the Net:

CDC health bulletin: http://www.cdc.gov/mmwr