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Acid fastness

The ability of the tubercle bacillus and other members of the genus Mycobacterium to retain certain dyes after treatment with a dilute mineral acid.  This enables these bacteria to be detected by microscopical examination of sputum and other clinical specimens in which they are seen as red rods against a green or blue counterstain background.

Acquired drug resistance

Resistance to anti-tuberculosis drugs developing in a patient due to sub-optimal therapy (usually not completing the course of treatment).

Active TB

TB bacteria are dividing and multiplying within an affected individual’s body, causing tissue and organ damage. A person with active TB is likely to be or soon become symptomatic.

Whether a patient sticks to their prescribed treatment programme.


Acquired Immune Deficiency Syndrome. This is the final stage in the course of HIV disease in which profound immunosuppression predisposes to certain aids-defining’ infections and other disease of which commonest across the world is tuberculosis.


The failure of a patient to respond immunologically to an infective challenge. This may be suggested by a negative tuberculin reaction in a patient with active tuberculosis.

Annual incidence (of tuberculosis)

The number of new cases of tuberculosis detected over the period of one year.


A molecule in, for example, a micro-organism that induces an immune response.

Artificial pneumothorax

An operation, commonly done in the days before anti-tuberculosis therapy, to collapse a lung by introducing air into the pleural cavity.


To withdraw a material or liquid using a syringe. Also used as a noun to refer to the aspirated material.

Atypical tuberculosis

See Environmental Mycobacteria.  Disease caused by environmental mycobacteria (mycobacteria common in the world around us) is sometimes called atypical tuberculosis, but this is an unfortunate misnomer as the two diseases are quite different in their behaviour. In particular, disease due to environmental mycobacteria is not infectious.

Autoimmune disease

Disease due to the immune system attacking parts of the host body rather than invading ‘foreign’ micro-organisms.

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