(CNN) -- The Fairfax County, Virginia, health department is investigating a tuberculosis outbreak at an area school after three people tested positive for the potentially fatal bacteria, officials said Thursday.
The health department has contacted 430 people who may have been exposed and need to be tested as a result of exposure to the three, the officials said.
Health officials declined to say whether the three were students or teachers.
They also said they did not know what strain of TB the three contracted.
The first case of tuberculosis at Robert E. Lee High School was diagnosed in December 2012, and the health department opened and completed an investigation, the agency said. But because two more people from the same school were diagnosed with it in June, the department re-opened the December case and is investigating whether they are related.
TB bacteria usually attack the lungs, but they can also attack other parts of the body such as the kidneys, spine and brain, according to the Centers for Disease Control and Prevention. If not treated properly, TB can be fatal.