TB - Glossary of terms

Glossary Of Terms

BCG - a vaccine for TB named after the French scientists Calmette and Guerin. This vaccine is currently used to help prevent tuberculosis, and is part of the UK vaccination programme.

Chemoprophylaxis - the administration of anti-tuberculosis drug(s) to prevent the acquisition or progression of tuberculosis infection. The former may be referred to as primary chemoprophylaxis or preventive therapy, the latter as secondary chemoprophylaxis.

Chest x-ray - a picture of the inside of your chest. A chest x-ray is made by exposing a film to x-rays that pass through your chest. A doctor can look at this film to see whether TB bacteria have damaged your lungs.

Contact - a person who has spent time with a person with infectious TB.

Culture - TB bacteria in your phlegm or other body fluids are grown and identified.

Directly observed therapy (DOT) - a way of helping patients take their medicine for TB. If you receive DOT, you will meet with a health care worker every day or several times a week. You will meet at a place you both agree on. This can be the TB clinic, your home or work, or any other convenient location. You will take your medicine at this place. Sometimes someone in your family or a close friend will be able to help you in a similar way to the health care worker.

Directly observed therapy, short-course (DOTS) - WHO has developed a control strategy known as Directly Observed Therapy, Short-course, which requires microscopy based diagnosis, standardised treatment under direct supervision, a secure supply of quality drugs and equipment, careful monitoring and supervision, and political commitment to support these activities.

Extra-pulmonary TB - TB disease in any part of the body other than the lungs (for example, the kidney or lymph nodes).

HIV infection - infection with human immunodeficiency virus, the virus that causes AIDS (acquired immunodeficiency syndrome). A person with both TB infection and HIV infection is at very high risk for TB disease.

Infectious TB - active tuberculosis disease which presents a risk of transmission of infection to others. For most practical purposes, this means sputum-smear-positive pulmonary tuberculosis in which acid fast bacilli (AFB) are present on direct microscopy of sputum. Disease of other parts of the respiratory tract or oral cavity, though rare, must also be considered infectious. Factors which increase infectiousness include the presence of cavities in the lungs, laryngeal tuberculosis and cough.

More stringent criteria with regard to infectiousness need to be applied if the patient is in contact with immunocompromised individuals or has drug-resistant disease.

Infectious person - a person who can spread TB to others because he or she is coughing TB bacteria into the air.

Isoniazid - a drug used to prevent TB disease in people who have TB infection. Isoniazid is also one of the five drugs used to treat TB disease.

Multi-drug resistant TB (MDR TB) - Tuberculosis resistant to isoniazid and rifampicin, with or without any other resistance.

Mycobacteria - the genus of bacteria which includes the organisms which cause tuberculosis (see below), but also bacteria of lower pathogenicity which are not transmitted person-to-person.

Mycobacteria tuberculosis complex - a group of closely related mycobacterial species ( M. tuberculosis, M. bovis and M. africanum) which can cause tuberculosis. Most infection in the UK is due to M. tuberculosis.

Pulmonary TB - TB disease that occurs in the lungs, usually producing a cough that lasts longer than 2 weeks. Most TB disease is pulmonary.

Resistant bacteria - bacteria that can no longer be killed by a certain drug.

Rifampicin - a drug used to prevent TB disease in people who have TB infection. Rifampicin is also one of the five drugs used to treat TB disease.

Sputum - phlegm coughed up from inside the lungs. Sputum is examined for TB bacteria using a smear; part of the sputum can also be used to do a culture.

Sputum Smear - a test to see whether there are TB bacteria in your phlegm. To do this test, lab workers smear the phlegm on a glass slide, stain the slide with a special stain, and look for bacteria on the slide. This test usually takes one day.

Tuberculosis (TB): disease due to infection with Mycobacterium tuberculosis complex.

Tuberculosis infection: a condition in which M. tuberculosis organisms are present in the body without necessarily causing active tuberculosis disease.

Active tuberculosis: currently active tuberculosis disease, whether or not it is infectious. The symptoms of disease include weakness, weight loss, fever, no appetite, chills and sweating at night. Other symptoms of TB disease depend on where in the body the bacteria are growing. If TB is in the lungs (pulmonary TB), the symptoms may include a cough, pain in the chest, and coughing up blood.

Sputum smear-positive tuberculosis (sometimes called 'open' tuberculosis): pulmonary tuberculosis in which mycobacteria ('acid-fast bacilli', AFB) have been seen in a stained smear of sputum examined under a microscope (see also 'Infectious tuberculosis' above). Confirmation of the diagnosis requires culture to differentiate the organisms from atypical mycobacteria.

Old/previous tuberculosis: tuberculosis disease which has either healed naturally or been fully treated and shows no evidence of current activity. It may or may not be latent (see below).

Latent tuberculosis (sometimes known as 'dormant' tuberculosis): a state in which viable mycobacteria are present in the body without currently causing active disease but with the potential to reactivate and cause disease. The latent focus may be the result of tuberculosis infection which has not progressed to cause disease, or old tuberculosis disease that is not currently active, eg calcified nodes on chest x-ray. An adequate course of chemoprophylaxis (or anti-tuberculosis treatment) is believed to effectively prevent a latent focus from reactivating in most patients for at least 20 years.

Reactivated tuberculosis: old tuberculosis infection (whether previously known or not) which has become active.

Re-infection: active tuberculosis due to acquisition of new infection in someone who has had previous tuberculosis infection.

Tuberculin - a reagent which is derived from inactivated tubercle bacilli is injected under the skin on the lower part of your arm in doing a TB skin test. If you have TB infection, you will probably have a positive reaction to the tuberculin.

Tuberculin skin tests - A skin test is carried out to determine if you may have been infected with tuberculosis. These are generally referred to as 'positive' or 'negative'.

Last reviewed: 21 March 2011