In a platoon where TB outbreak occurred, we performed low dose chest CT (LDCT), QuantiFERON-TB gold in tube (QFT) and two-step (0, 4weeks) TST for outbreak investigation. We perform QFT at 0, 2, 4, 8 and 12 weeks after initial investigation for soldiers with negative QFT results, and soldiers with positive QFT and normal LDCT took isoniazid and rifampin for 3 months as treatment of latent TB.