For which group does an induration of ≥ 15 mm suggest a positive reaction regardless of risk factors?

An induration of ≥ 15 mm is significant and indicates a positive reaction in individuals with no known risk factors. This measurement serves as a threshold for assessing tuberculosis (TB) exposure in those who are otherwise considered to be at low risk. In general, the criteria for interpreting a positive result from a Tuberculin Skin Test (TST) vary depending on the individual's risk factors for TB.

For the group identified within this question, a reading of 15 mm or more indicates a robust immune response sufficient to suggest TB infection, regardless of whether the individual has any heightened risk factors. This guideline is set to ensure that individuals who are not known to be in higher-risk classifications, such as healthcare workers or residents of congregate settings, are still evaluated thoroughly for TB exposure when this size of induration is present.

For individuals in congregate settings, healthcare workers, or those under the age of 4, the threshold for what constitutes a positive test is lower due to their increased vulnerability and exposure risks.