But chest X-rays of those testing positive were normal, prompting officials with the East Metro Health District to determine that the 20 people do not have tuberculosis and are not contagious to others.

Last month, a female student at Lilburn Middle School was diagnosed with the disease. Health officials tested 226 people, 18 testing positive for TB infection.

After an active tuberculosis case was diagnosed for a student at Rockbridge Elementary, health officials tested 66 people. Two tested positive for TB infection.

Six to nine months of preventive antibiotic medication will be recommended for the 20 people who tested positive, health district officials said.

Health officials in late spring will retest people at the schools who initially tested negative to determine if any of them have been incubating TB germs and might later test positive.

TB is spread when an active TB case coughs or sneezes and others breathe in the infectious airborne bacteria. Those who test positive to a TB skin test may have a latent infection that can require medical treatment.

Many with latent TB never develop the active form. But if left untreated, the condition can become active.

(Copyright 2004 by The Associated Press. All Rights Reserved.)