Final answer:
A TB test is considered positive for children under 5 years old with an induration >5mm. This indicates exposure to Mycobacterium tuberculosis. BCG vaccination can affect the test's accuracy.
Step-by-step explanation:
For which population is a TB test considered positive if the induration is >5mm? Specifically, children under 5 years old are among the populations for whom an induration of >5mm following a Mantoux tuberculin skin test is considered a positive result for tuberculosis (TB). The Mantoux test is a method used to detect exposure to Mycobacterium tuberculosis, the bacterium that causes TB.
During the test, a small amount of tuberculin protein derivative is injected into the skin, and the area is then observed for a reaction after 48-72 hours. A positive reaction is indicated by redness, swelling, or hardness in the injected area and is measured in millimeters. The presence of an induration of 5mm or larger in children under the age of 5 suggests that they have been exposed to the bacteria and that their immune system has mounted a cellular response. This is critical for early detection and treatment in a population vulnerable to severe TB disease.
Considerations for TB Screening and Diagnosis
It's important to note that BCG vaccinations, commonly administered in some countries, can lead to false-positive results in the Mantoux test. Health professionals must take into account a patient's vaccination history and may require additional diagnostic methods, such as chest radiographs, to confirm a TB diagnosis.