The following terms and abbreviations are used in this report.
Acid-fast bacilli (AFB). Microorganisms that are distinguished by their retention of specific stains even after being
rinsed with an acid solution. The majority of AFB in patient specimens are mycobacteria, including species other than
Mycobacterium tuberculosis complex. A positive nucleic acid amplification (NAA) or culture result is needed for confirmation of
M. tuberculosis complex. The relative concentration of AFB per unit area on a slide (the smear grade) is associated
Anergy. A condition wherein a person has diminished ability to exhibit delayed T-cell hypersensitivity reaction to
antigens because of a condition or situation resulting in altered immune function. When referring to inability to react to a skin test,
the correct term is cutaneous anergy. Skin tests for anergy (i.e., control antigens) have poor predictive value and are
Associate contact. A person who is somehow affiliated with a patient who has noninfectious tuberculosis (TB) or
with another contact. Often used in connection with source-case investigations; does not imply an
M. tuberculosis transmission pathway.
Bacille Calmette-Guérin (BCG). A vaccine for tuberculosis named after the French scientists Calmette and Guérin.
The vaccine is effective in preventing disseminated and meningeal TB disease in infants and young children. It might
have approximately 50% efficacy for preventing
smear-diagnosed pulmonary TB in adults. It is used in multiple countries
where TB disease is endemic.
Boosting. When nonspecific or remote sensitivity to
tuberculin (purified protein derivative [PPD] in the skin test) wanes
or disappears with time, subsequent tuberculin skin tests can restore the sensitivity. This is called boosting or the
booster phenomenon. An initially limited reaction size is followed by a larger reaction size on a later test, which can be confused with
a conversion or a recent M. tuberculosis infection. Two-step testing is used to distinguish new infections from boosted
reactions in infection-control surveillance programs, but this method is not recommended for testing contacts.
Bronchoscopy. A procedure for examining the lower respiratory tract that requires inserting the end of an endoscopic instrument through the mouth or nose (or tracheostomy) and into the respiratory tree. It can be used to obtain
diagnostic specimens. It also creates a high risk for
M. tuberculosis transmission to health-care workers if it is used on a patient who
has TB (even if the patient is smear negative), because the procedure induces coughing.
Bronchoalveolar lavage (BAL). A procedure for collecting respiratory specimens from the airway, typically
during bronchoscopy. Sterile saline is flushed through an airway, and the resultant mixture of cells, secretions, and saline is
aspirated for studies (e.g., microscopy and culture).
Case. A particular instance of a disease (e.g., TB). A case is detected, documented, and reported.
Cavity (pulmonary). A hole in the lung parenchyma, typically not involving the pleural space. Although multiple
causes can account for a lung cavity, and its appearance is similar regardless of its cause, in pulmonary TB, it results from
the destruction of pulmonary tissue by direct bacterial invasion and an immune interaction triggered by
M. tuberculosis. A tuberculous cavity large enough to see with a normal chest radiograph predicts infectiousness.
Contact. Refers to someone who has been exposed to
M. tuberculosis infection by sharing air space with a person
with infectious TB.
Contagious. Refers to TB disease of either the lungs or the throat that has been demonstrated to have caused
transmission to other persons or the patient who has TB disease.
Conversion. A change in the result of a test for
M. tuberculosis infection that is interpreted to indicate a change from
being uninfected to infected. With the tuberculin skin test, an increase of
>10 mm in induration size during
<2 years is defined as a conversion. A conversion is presumptive evidence of new
M. tuberculosis infection and poses an increased risk for
progression to TB disease. The term is applied to contacts only when previous skin test results are available. A change in
tuberculin status during the window period is not necessarily consistent with this definition.
Delayed-type hypersensitivity (DTH). Cell-mediated
inflammatory reaction to an antigen that is recognized by
the immune system, typically because of previous exposure to the same or similar antigens. Cell-mediated reactions are
contrasted with an antibody (or humoral) response. DTH typically peaks 48--72 hours after exposure to the antigen.
Directly observed therapy (DOT). An
adherence-enhancing strategy in which a health-care worker or other trained
person watches a patient swallow each dose of medication and is
accountable to the public health system. DOT is the preferred
method of care for all patients with TB disease and is a preferred option for patients under treatment for latent infection.
Disseminated TB. See Miliary TB.
Drug-susceptibility test. A laboratory determination to
assess whether an M. tuberculosis complex isolate is susceptible
or resistant to anti-TB drugs that are added to mycobacterial growth medium. The results predict whether a specific drug is
likely to be effective in treating TB disease caused by that isolate.
Enabler. A practical item given to a patient for making
adherence (e.g., to treatment or to clinic appointments) easier.
Exposure. The condition of being subjected to something (e.g., an infectious agent) that could have an effect. A
person exposed to M. tuberculosis does not necessarily become
infected. Much of the work in a TB contact investigation is
dedicated to learning who was exposed and, of these, who became
Exposure period. The coincident period when a contact shared the same air space as a person with TB during
the infectious period.
Exposure site. A location that the index patient visited during the infectious period (e.g., a school, bar, bus, or residence).
Immunocompromised and immunosuppressed. Conditions in which at least part of the immune system is functioning
at less than normal capacity. According to some style experts, immunocompromised is the broader term,
and immunosuppressed is restricted to conditions with iatrogenic causes, including treatments for another condition.
Some immunocompromised conditions increase the likelihood that
M. tuberculosis infection will progress to TB disease.
Certain conditions also make TB disease or infection from
M. tuberculosis more difficult to diagnose because manifestations of
TB disease differ, and tests for infection rely on an intact immune system.
Incentive. A gift given to patients to encourage or acknowledge their adherence to treatment.
Index. The first case or patient that comes to attention as an indicator of a potential public health problem. Contrast
Induration. The firmness in the skin test reaction. Induration is produced by immune-cell infiltration in response
to tuberculin antigen that was introduced into the skin. It is measured by palpation transversely, and the result is recorded
in millimeters (mm). The measurement is compared to guidelines to determine whether the test result is classified as positive
Infection. A condition in which microorganisms have
entered the body and typically have elicited immune responses.
M. tuberculosis infection might progress to TB disease. The expression
M. tuberculosis infection includes both latent
infection and TB disease. Latent M.
tuberculosis infection or latent tuberculosis infection (LTBI) is an asymptomatic condition that
follows the initial infection; the infection is still present but is dormant (and believed not to be currently progressive or invasive).
TB disease is determined by finding anatomic changes caused by advancing infection (e.g., shadows from infiltrates on a
chest radiograph) or by noting symptoms (e.g., malaise, feverishness, or cough), and typically by both. Positive culture results for
M. tuberculosis complex typically are interpreted as both an indication of TB disease and its confirmation, but infecting
organisms can be obtained from patients who have no other evidence of disease.
Infectious. Refers either to TB disease of the lungs or throat, which has the potential to cause transmission to other
persons, or to the patient who has TB disease.
Isoniazid (INH). A highly active anti-TB chemotherapeutic agent that is a basis of treatment for TB disease and
Laryngeal TB. A highly infectious form of TB disease, with erosive, exudative invasion of the larynx.
Latent M. tuberculosis infection (or latent tuberculosis infection [LTBI]).
Mantoux method. A skin test performed by intradermally injecting 0.1 mL of PPD tuberculin solution into the volar
or dorsal surface of the forearm. This is the recommended method for tuberculin skin testing.
Meningeal TB. A highly dangerous and
difficult-to-diagnose form of TB disease with infectious invasion of the
tissues covering the brain. Often indolent but uniformly fatal if
untreated, at times it is diagnosed too late to save the patient's life
or prevent permanent disability.
Miliary TB. Sometimes referred to as disseminated TB. A dangerous, and difficult to diagnose, form of rapidly
progressing TB disease that extends throughout the body. Uniformly fatal if untreated, sometimes it is diagnosed too late to save a
life. Derives its names from a pathognomonic chest radiograph, but certain patients with this condition have normal findings
or ordinary infiltrates on the chest radiograph.
Multidrug-resistant TB (MDR TB). TB disease caused by an
M. tuberculosis strain that is resistant to at least INH
and rifampin. Treatment regimens for curing MDR TB are long, expensive, and difficult to tolerate. The cure rate
depends on the susceptibility of M.
tuberculosis to alternative chemotherapy.
Mycobacterium bovis (M. bovis). A member organism of
M. tuberculosis complex and the causative infectious agent of
TB in cattle. It also causes infection and disease in humans, who become infected by consuming unpasteurized dairy
products from tuberculous cows. Human M.
bovis TB disease has certain distinctive characteristics but in practical terms
is indistinguishable from human-variant TB. Human pulmonary
M. bovis TB disease probably is transmissible to other
humans by the airborne route, and secondary cases can result, especially among vulnerable contacts.
Mycobacterium tuberculosis (M.
tuberculosis). The namesake member organism of
M. tuberculosis complex, and the most common causative infectious agent of TB disease in humans. At times, the species name refers to the
entire M. tuberculosis complex, which includes
M. bovis and five other related species.
Nucleic acid amplification (NAA). A laboratory method used to target and amplify a single DNA or RNA sequence
for detecting and identifying (typically) a microorganism. NAA tests for
M. tuberculosis complex are sensitive and specific;
they can accelerate confirmation of pulmonary TB disease.
Purified protein derivative (PPD) tuberculin. A material used in diagnostic tests for
M. tuberculosis infection. In the United States, PPD solution (5 tuberculin units per 0.1 mL) is approved for administration as an intradermal injection as
a diagnostic aid for M. tuberculosis infection (latent infection or TB disease). PPD tuberculin also was one of the antigens in
the first-generation QuantiFERON-TB test.
QuantiFERON®-TB test. An in vitro cytokine assay that detects cell-mediated immune response (see also DTH)
to M. tuberculosis in heparinized whole blood from venipuncture. This test requires only a single patient encounter, and the
result can be ready <1 day. In 2005,
QuantiFERON®-TB is being replaced by
QuantiFERON®-TB Gold, which has
greater specificity because of its synthetic antigens.
QuantiFERON®-TB Gold appears capable of distinguishing between
the sensitization caused by M. tuberculosis infection and that caused by BCG vaccination.
Radiography. The diagnostic imaging techniques (including plain-film chest radiographs and computerized
tomography) that rely on degrees of X-radiation transmission related to differences in tissue densities.
Secondary (TB) case. A new case of TB disease that is
attributed to recent (i.e., <2 years) transmission as part of a
scenario under investigation. Technically, all cases are secondary, in the sense that they arise from other cases that are contagious.
Secondary (or "second-generation") transmission.
Transmission of M. tuberculosis from persons with secondary cases
(see Secondary (TB) case). This creates a chain of transmission, and if secondary transmission is identified as part of a
contact investigation, the scenario can be classified as an outbreak.
Smear. A laboratory technique for preparing a specimen so bacteria can be visualized microscopically. Material from
the specimen is spread onto a glass slide (and typically dried and stained). Smear, stain, and microscopy methods for mycobacteria are specific to this genus (see AFB). The slide can be scanned by light or fluorescent high-power microscopy. These
methods require ongoing quality assurance for prompt and reliable results. The results for sputum AFB smears typically are reported
as numbers of AFB per high-powered microscopy field, or else as a graded result, from no AFB to 4+ AFB. The quantity
of stained organisms is associated with degree of infectiousness.
Source case or patient. The case or person that was the original source of infection for secondary cases or contacts.
The source case can be, but is not necessarily, the index case.
Specimen. Any bodily fluid, secretion, or tissue sent to a laboratory for testing.
Sputum. Mucus containing secretions coughed up from within the lungs. Tests of sputum (e.g., smear and culture)
can confirm pulmonary TB disease. Sputum is different from saliva or nasal secretions, which are unsatisfactory specimens
for detecting TB disease. However, specimens suspected to be inadequate should still be processed because positive cultures
can still be obtained and may be the only bacteriologic indication of disease.
Suspected TB. A tentative diagnosis of TB that will be confirmed or excluded by subsequent testing. Cases should
not remain in this category for >3 months.
Symptomatic. A term applied to a patient with
health-related complaints (i.e., symptoms) that might indicate the
presence of disease. At times, the term is applied to a medical condition (e.g., symptomatic pulmonary TB).
TB disease. See discussion under Infection.
Treatment for LTBI. Treatment that prevents the progression of infection into TB disease.
Tuberculin. A precipitate made from a sterile filtrate of
M. tuberculosis culture medium.
Tuberculin skin test (TST). A diagnostic aid for finding
M. tuberculosis infection. A small dose of tuberculin (see
also Mantoux method and PPD) is injected just beneath the surface of the skin by the Mantoux method, and the area
is examined for induration by palpation 48--72 hours after the injection. Indurated margins should be read
transverse (perpendicular) to the long axis of the forearm.
Tuberculin skin test conversion. See Conversion.
Tuberculosis (TB). A clinically active, symptomatic disease caused by infection with a member of the
M. tuberculosis complex.
Two-step (tuberculin) skin test. A procedure used for baseline skin testing of persons who will periodically receive TSTs (e.g., health-care workers or residents of long-term--care facilities) to reduce the likelihood of mistaking a boosted
reaction for a new infection. If an initial TST result is classified as negative, a second test is repeated 1--3 weeks later. If the reaction to
the second TST is positive, it probably represents a boosted reaction, indicating that the infection was most likely in the past
and not recent. If the second TST is also negative, the person is classified as not being infected. Two-step skin testing has no
place in contact investigations or in other circumstances in which ongoing transmission of
M. tuberculosis is suspected.
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Date last reviewed: 12/9/2005