Once the old tuberculosis has relapsed, there is a possibility that it may be contagious, which needs to be determined by the situation. 1. Infectious: Some of the patients with tuberculosis relapse are infectious to a certain extent, and Mycobacterium tuberculosis can be found through sputum testing, which means it is infectious. Therefore, patients with old tuberculosis need to be examined regularly, and it is recommended that they be reexamined once a year to avoid recurrence of the disease. 2. No contagiousness: if the patient’s lesion density is relatively high, suggesting that the condition is relatively stable, this situation is generally inactive and not contagious, and if no Mycobacterium tuberculosis is found through the sputum test of tuberculosis patients, it is generally not contagious. Therefore, patients are advised that it is necessary to undergo regular review and need to actively seek treatment in the event of a flare-up.