The infectiousness of tuberculosis mainly comes from the sputum of patients with active tuberculosis. As long as Mycobacterium tuberculosis can be found in the sputum, it indicates that the patient is infectious. It does not indicate active tuberculosis, nor does it necessarily indicate infectiousness. Only patients with confirmed sputum with Mycobacterium tuberculosis are clinically diagnosed with active, open tuberculosis, and these patients need to be isolated because they are the source of tuberculosis infection.