TB is clinically classified into type V, type I, type II, type III, type IV, and type V. Among the above type V TB, type III TB is also called secondary TB. Among the above type V tuberculosis, type III tuberculosis is also called secondary tuberculosis, especially infiltrative tuberculosis and chronic fibro-cavernous tuberculosis are the most infectious. Patients are prone to cough, sputum, blood in sputum, hot flashes, night sweats, and weight loss. In particular, chronic fibrous cavity tuberculosis is the most infectious because the sputum of patients is chronically positive for antacid bacilli. Clinical treatment is very tricky and drug-resistant tuberculosis is easily formed, causing great pain to patients and spreading to the surrounding population. Therefore, once diagnosed with chronic fibro-cavitary TB, active and standardized anti-tuberculosis treatment is needed to avoid delaying the diagnosis and causing drug-resistant TB or transmission to more people. In conclusion, patients with positive sputum test for antacid bacilli in pulmonary tuberculosis are the most infectious and are mainly seen in type III tuberculosis, which is the infiltrative form of secondary tuberculosis and chronic fibro-cavernous tuberculosis.