Final answer:
A positive TB skin test with an induration of ≥5mm for high-risk individuals indicates exposure and an immune response to Mycobacterium tuberculosis. It doesn't confirm active infection, thus further evaluation is necessary. BCG vaccination can lead to false positives in skin testing.
Step-by-step explanation:
High-Risk Populations for TB and the Significance of a Positive Skin Test
In the context of the Mantoux tuberculin skin test, certain populations are considered high risk for tuberculosis (TB) infection. These include individuals with HIV, those who have had recent contact with someone with active TB, persons with chest radiographs suggesting previous TB infection, and those with immunosuppression for other reasons, such as organ transplant recipients or individuals receiving immunosuppressive drugs.
The significance of a positive skin test result, with an induration of ≥5mm in these high-risk populations, indicates that there has been exposure to Mycobacterium tuberculosis and a cellular immune response is present. However, a positive test does not necessarily mean there is an active TB infection. It means that the patient has either an active infection or a latent TB infection and further medical evaluation is needed, such as a chest radiograph or a sputum test, to determine if the TB bacteria are causing disease. It's important to note that previous vaccinations with the BCG vaccine can cause false-positive results, specifically in countries where the BCG vaccine is widely used.