Latent tuberculosis

Latent tuberculosis (LTB), also called latent tuberculosis infection (LTBI), is a condition that occurs when a person is infected with the bacterium Mycobacterium tuberculosis but does not have active tuberculosis (TB). The active form of the disease can be contagious, while the latent form is not; therefore, it is impossible to catch TB from someone with LTB. For LTB, various treatment regimens are used, generally requiring several months for completion.

Epidemiology

As of 2023, it is estimated that one-quarter of the world's population has latent or active TB. TB is estimated to have newly infected 10.8 million people per year.

The spread of TB is uneven throughout the world: approximately 80% of the populations in many Asian and African countries test positive on tuberculin tests, while only 5–10% of the US population tests positive.

Transmission

Latent disease

It is impossible to catch TB from someone with LTB. In people who develop active TB of the lungs—also called pulmonary TB—the Mantoux test is often positive. Such people are contagious and can pass the bacteria to others. TB can be transmitted by exhalation. Tiny droplets exhaled by a person with active TB can remain suspended in the air for several hours, depending on environmental conditions. Another person could then inhale these droplets and potentially become infected with TB. However, such infection is unlikely to occur, because infection generally requires longer exposure. This reduced probability includes brief exposures that occur when a person is exposed to TB during brief social contact; prolonged exposure (over two months or so, e.g., by living with a relative with TB) is generally required for TB infection.