The announcement brings to three the number of people being treated for the disease since a student developed symptoms last month. All three are out of school receiving treatment and further testing and won’t return until they are cleared, according to Ketty Gonzalez, the district director for the East Central Health District.

The health department tested 500 individuals who were possibly exposed after the first confirmed case. Of the 500, 75 tested positive for TB bacteria, including several who were in close proximity to the first student, she said.

However, a positive test for TB bacteria is no indication an individual will develop the disease, or when the infection took place. In Richmond County, about 15 percent of the population tests positive for TB bacteria, but 90 percent of those who test positive never develop the disease.

The once-common disease is rare now. There were only six active cases in 2010 and five in 2011 in Richmond County, Gonzalez said.

Fifty of the 500 tested never returned for their test to be read, but they are advised to do so, she said.

Carol Rountree, the executive director of student services for the Richmond County Board of Education, praised collaboration between the health department and school system to address the health issue. Parents and students shouldn’t worry, but staff will continue to be available to answer any questions, she said.

“We’ve been assured that this is not outside the norm, and there’s no reason for us to be distressed,” she said.