Guidelines on the Prevention and Control of Tuberculosis in Ireland

<strong>Guidelines</strong> on the Prevention and Control of Tuberculosis in Ireland 2010HSE/HPSCGlossary of TermsAcid-fast Bacilli: Bacteria which having been stained with a dye, retain their colour in acid alcohol. Usedas a technique for microscopic detection of mycobacteria. The relative concentration of AFB per unit areaon a slide (the smear grade) is associated with infectiousness. A positive culture is required for laboratoryconfirmation of M. tuberculosis complex.Active TB: Infection with mycobacteria of the M. tuberculosis complex, where mycobacteria are growingand causing symptoms and signs of disease. This is distinct from LTBI where mycobacteria are present butare inactive and not causing symptoms of disease. The diagnosis of active TB is made most often on thebasis of positive bacteriology but in approximately 15%-25% of cases on the basis of appropriate clinicaland/or radiological and/or pathological presentation as well as treatment response.Adherence: This refers to the patient’s ability or choice to adhere to a treatment regimenAerosol: Small droplets of moisture that are exhaled or coughed up. In a patient with pulmonarytuberculosis they may contain Mycobacterium tuberculosis bacteria that are suspended in the air andlead to the spread of infection. Generation of infectious aerosols is greatest with laryngeal and cavitarypulmonary disease.Air changes per hour (ACH): The number of air changes per hour in a room; one air change being avolume of air equal to the room volumeAirborne isolation: The conditions into which a patient with suspected or proven active tuberculosis maybe placed for purposes of preventing transmission to other persons. In most institutional settings airborneisolation is provided by a combination of increased ventilation (e.g. in the room occupied by the patient)and the use, by staff or visitors, of personal protective wear (respirators that filter 95% of particles of 1micron or larger and have less than 10% leak).Anergy: A condition wherein a person has diminished ability to mount a delayed T-cell hypersensitivityresponse to antigens because of a condition or situation resulting in altered immune function e.g. HIVinfection. When referring to an inability to react to a skin test, the correct term is “cutaneous anergy”.Bacille Calmette-Guerin (BCG) vaccine: A live attenuated vaccine derived from Mycobacterium bovis usedto prevent tuberculosis diseaseBAL: Bronchoalveolar lavage. This is a diagnostic procedure in which small amounts of physiologicalsolution (sterile saline solution) are injected through a fibreoptic bronchoscope into a specific area ofthe lung, while the rest of the lung is sequestered by an inflated balloon. The fluid is then aspirated andinspected for pathogens, malignant cells, and mineral bodies. BAL is typically performed to diagnose lungdisease.Booster phenomenon: The presence of an initially negative TST response followed by a positive responsewhen the test is repeated at any time from 1 week to 1 year later. The phenomenon often occurs manyyears after infection, most notably in the elderly. The initial negative response is based on the subject’sinitial failure to “recall” immunologically, prior infection. To avoid inadvertent labelling of a positiveresponse as due to TST conversion, especially when serial skin testing is planned, initial two-step skintesting may be recommended.Cavitary disease: This is a radiological-pathological label referring to evidence of lung destruction,i.e. evidence on chest X-ray or pathology of cavities or cystic areas that communicate with a bronchus.Cavities generally harbour large numbers of bacteria and, as a result, patients with cavitary disease tend tobe highly infectious.Chemopropylaxis: Treatment of LTBI. The administration of anti-tuberculosis drug (s) to prevent theacquisition of LTBI or progression of LTBI to active TB disease.-188-