Final answer:
A TB induration >15 means there is a positive Mantoux tuberculin skin test indicating exposure to TB and cellular immune response. False positives can occur, especially in those previously vaccinated with BCG. Verification of active TB requires additional tests, despite the 10% Type I error and 20% Type II error rates associated with the screening.
Step-by-step explanation:
An induration greater than 15 millimeters resulting from a Mantoux tuberculin skin test indicates a positive reaction, suggesting that the individual has been exposed to Mycobacterium tuberculosis and has developed a cellular immune response. This assessment is part of screening for potential TB exposure and relies on measuring the hard, raised red area that appears a couple of days after administering the test. A positive test does not necessarily mean active TB infection; it signifies that the individual's immune system has been sensitized to the tuberculin protein due to a previous or current exposure.
However, there are several factors that can impact the accuracy of the test. For example, a false-positive result can occur in individuals previously vaccinated with the BCG vaccine. Additionally, the test has a 10 percent probability of a Type I error, indicating a 10 percent chance of a false positive, while there is also a 20 percent probability of a Type II error, referring to a 20 percent chance that it will fail to detect TB when it is indeed present.
To confirm an actual case of TB, especially when symptoms or chest radiographs suggest the presence of an infection, further testing, such as chest radiographs for Ghon complex formation, is necessitated. This follows the understanding that a positive Mantoux test means exposure and an immune response but not necessarily a current, active infection.