Final answer:
The Mantoux tuberculin skin test can result in false-positive readings in individuals vaccinated with BCG due to the immune response to similar bacterial proteins. This limits the test's usefulness in areas where BCG is commonly administered, necessitating additional diagnostic methods such as chest radiographs.
Step-by-step explanation:
In countries where the Bacillus Calmette-Guérin (BCG) vaccine is used, people who have been vaccinated may show a positive reaction to the Mantoux tuberculin skin test. This happens because the test detects the immune response to components of the TB bacteria, which is similar to the response generated by the vaccine. Therefore, a positive result in such cases may not indicate active tuberculosis infection but rather a prior BCG vaccination or exposure to the TB bacteria.
The tuberculin skin test is a classical test for delayed hypersensitivity. A positive result, indicated by a raised red area called an induration, shows that the patient's immune system has been exposed to bacterial proteins from M. tuberculosis and has mounted a cellular immune response. However, this positive reaction does not necessarily mean a current infection; it could be a response to the BCG vaccine or a past TB infection.
Because of this, the usefulness of the tuberculin skin test in areas where BCG vaccination is prevalent can be limited. Chest radiographs are often used concurrently to help confirm active tuberculosis by detecting the presence of a Ghon complex.