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FAIRFAX, Va. (WUSA9) -- Fairfax County Health Department announced three cases of tuberculosis on Thursday afternoon. Two of the recent cases reportedly involved students at Robert E Lee High School in Fairfax.

More than400 people who may have been exposed to tuberculosis are now being screened in Fairfax County.

An investigation was initiated in December 2012 into one case of TB. However, two more cases this month at the same school prompted the health department to reopen the December case, Director of Health for Fairfax County Dr.Gloria Addo-Ayensusaid in a news conference. All three cases are now being reviewed together, officials said at a news conference.

Fairfax County and the health department say they are exercising an abundance of caution and have sent a letter encouraging those who could have been exposed to come forward and get tested. The school's health department will also hold special clinics at the school next week.

Dr. Barbara Andrino, a TB physician for the Fairfax County Health Dept., said when an individual has active TB and coughs, bacteria travels through the air and can be breathed in by another individual.

Symptoms include coughing, sneezing, fever, chills and sudden, unexplained weight loss.

The health department says it investigates 90 cases of TB each year.

Fairfax County is not saying if the three individuals were students in order to protect their privacy. The Washington Post reports that the two most recent cases involved students.