DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
TB skin test on a 55-year-old woman. Close-up of a red patch of skin, indicating a positive result to the Heaf test for tuberculosis (TB). Multiple tiny punctures in the skin show where the testing device was applied. A positive result to a Heaf test is triggered by an immune reaction by the patient's antibodies against Mycobacterium tuberculosis, the bacteria that causes TB. This indicates exposure to TB, either through vaccination or infection. TB is an infectious and debilitating lung disease that is sometimes fatal.
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