Taking isoniazid for more than twenty days may still be infectious. General treatment of tuberculosis requires early, moderate, combined, regular, and full course drug therapy to maximize the killing of tubercle bacilli. Usually, the combination of isoniazid, rifampicin, ethambutol and pyrazinamide is needed for 6 to 9 months or even longer to maximize the killing of tuberculosis bacilli while avoiding transmission to others. Taking isoniazid for more than twenty days, the course of treatment is relatively short, even if the medication is more effective, it does not ensure that the tubercle bacillus is completely killed, or open tuberculosis is effectively controlled, there may still be infectious. You can go to the hospital to check the sputum smear, sputum culture or sputum gene sequencing, to determine whether there is tuberculosis bacilli in the sputum, and if there is, it means that it is still infectious, and it needs to be isolated appropriately.