Which statement best distinguishes latent tuberculosis infection from active tuberculosis?

• A. Positive TST/IGRA with symptoms and abnormal CXR
• B. Negative TST/IGRA with no symptoms
• C. Positive TST/IGRA with no symptoms and normal CXR
• D. Positive cultures with symptoms

Answer: (C)

Latent TB infection occurs when someone has been infected and shows an immune response (positive TST or IGRA) but has no TB symptoms and a normal chest X-ray. There is no active disease or contagious infection. This contrasts with active TB, where symptoms such as a persistent cough, fever, night sweats, or weight loss are present, the chest X-ray often shows abnormalities, and microbiologic evidence (positive cultures or smears) confirms active disease. So the statement describing a positive TST/IGRA with no symptoms and a normal CXR best represents latent TB infection.