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Tuberculosis

Positive PPD

07/09/2007

Question:

I have taken a PPD test 2 years ago it was positive, I work in a Medical clinic so I have to take a test every year, because it was positive then I have never take an other test since then, I was born in Mexico and I had a BCG vaccine given when I was young my question is: because of this vaccine is that my test was positive?

Answer:

No, most people who receive the BCG vaccine have negative tuberculosis skin tests or PPD. Most people born in Mexico receive BCG just after birth. If you are more than 10 years old, then your skin test reaction is unlikely to be related to prior BCG vaccination. The Centers for Disease Control considers a skin test reaction of 10 mm or more to be positive in a person born in Mexico. If your skin test was at least 10 mm in size then we would consider it positive. This means that you have been exposed to the TB infection. If your chest x-ray is normal and you have no symptoms then you have latent tuberculosis infection or a sleeping form of the infection. Most TB experts would recommend that you take a course of medication to prevent tuberculosis in the future. This medication is called isoniazid. If you take isoniazid for 9 months you can reduce the risk of developing active tuberculosis by more than 90%.

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Response by:

Catherine A Curley, MD, MS Catherine A Curley, MD, MS
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University