At least 80 students, teachers and staff at Ennis High School have tested positive for exposure to tuberculosis.
The skin tests were ordered because a teacher now on medical leave was diagnosed with the bacterial infection just before the first day of school.
Dr. Brian Smith of the Texas Department of State Health Services, said people who a positive skin test normally are not sick and are not infectious.
"What a positive skin test means is that a person has been exposed to the disease and they have picked up a tiny bit of the bacteria that has caused their body to react to the skin test, so in those persons you can kill the bacteria by giving a single medication for nine months," he said.
Those who tested positive are now being told to get chest X-rays at Baylor Medical Center in Waxahachie.
Sixteen-year-old Shabrekia Richardson found out Friday her skin test came back positive.
"I was shocked," the high school junior said. "I actually started crying. ... I just thought, 'I'm in a school.' I never thought in a school I could get something like this."
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In all, 235 people at the high school were tested last week. The school has a student enrollment of 1,580.
In a letter to families, the school district said a larger number of students had tested positive than it expected.
"There's a lot of unanswered questions like what to do next, what's going to happen, am I going to be able to go to school?" Richardson said.
But Smith said those who tested positive do not need to stay out of school unless they show symptoms of tuberculosis.
"I wouldn't keep anybody out of school for having a positive skin test unless they also have a severe cough or severe weight loss or other symptoms of tuberculous," he said. "Normally those people are going to stay in school, even with a positive skin test."
Richardson's father, Wendall, said he is having the entire family tested, including her 6-month-old sister.
"It's just a bad situation," he said. "It got out of hand. It could have been avoided, you know, if the teacher -- if teachers period -- had of been screened every couple of months."
Dr. Cedric Spak, an infectious disease consultant at Baylor Medical Center, said families should not panic about positive tests.
"If you get a positive skin test, that means you have a 10 percent chance in your life of developing TB -- which means you have a 90 percent chance of developing nothing," he said.