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Note: Unless otherwise specified, the definitions listed below apply to the terms as used in this handbook. They may have different meanings in other contexts.
Active (TB) case-finding: Provider-initiated screening and testing in communities by mobile teams, often using mobile X-ray and rapid molecular tests. The term is sometimes used synonymously with “systematic screening”. It is referred to as “intensified case-finding” when conducted in health-care facilities and as “enhanced case-finding” when conducted in communities.
Close contact: A person who does not live in the household but who shared an enclosed space, such as a social gathering place, workplace or facility, with the index patient for extended periods during the day during the 3 months before the current disease episode commenced.
Computer-aided detection (CAD): refers to the use of specialized software to interpret abnormalities on chest radiographs that are suggestive of TB. The results are expressed as abnormality scores. CAD may be used for screening or triage.
Contact: Any person who has been exposed to a person with TB disease.
Contact investigation: systematic identification of people with previously undiagnosed TB disease and TB infection among the contacts of an index TB patient in the household and in comparable settings in which transmission occurs. It consists of identification, clinical evaluation and/or testing and provision of appropriate anti-TB therapy (for people with confirmed TB) or TB preventive treatment (for those without TB disease). This term is often used synonymously with “contact tracing”; however, in the context of TB, action beyond identifying contacts is critical.
Household contact: A person who shared the same enclosed living space for one or more nights or for frequent or extended periods during the day with the index patient during the 3 months before the start of current treatment.
Index patient (index case): A person of any age with new or recurrent TB initially identified in a specific household or comparable setting in which others may have been exposed. An index patient is the person on whom a contact investigation is centred but is not necessarily the source.
Initial screening: The first screening test, examination or other procedure applied in a population eligible for screening.
Number needed to screen: The number of persons that need to undergo screening in order to diagnose one person with of TB disease.
Passive TB case-finding: A patient-initiated pathway to TB diagnosis involving: (1) a person with TB disease who experiences symptoms that he or she recognizes as serious; (2) the person having access to and seeking care and presenting spontaneously at an appropriate health facility; (3) a health worker correctly assessing that the person fulfils the criteria for presumptive TB; and (4) successful use of a diagnostic algorithm with sufficient sensitivity and specificity to diagnose TB.
Patient-initiated health care pathway: The patient-initiated pathway to TB diagnosis relies on patients seeking care and on health systems to respond quickly and appropriately. Some people may access care after exposure if they are very well informed, but most people will seek care only once they experience symptoms severe enough to merit attention. They may experience delay due to access barriers. On accessing care, they may experience delays until they are referred to a service that can make a TB diagnosis, and there may be further delays and barriers before a diagnosis is made and appropriate treatment is initiated.
Provider-initiated TB screening pathway: The provider-initiated TB screening pathway systematically targets people at high risk of exposure or of developing TB disease and screens them by assessing symptoms, using tests, examinations or other procedures to identify those who might have TB, following up with a diagnostic test and additional clinical assessments to make a definite diagnosis. This approach can target people at different stages of TB, for example by screening those at high risk of exposure (e.g. high TB burden communities or settings such as prisons) or those who are exposed to TB (e.g. contacts of a TB patient), or those who have high risk of developing TB (e.g. people living with HIV). Screening programmes must include an appropriate pathway for diagnostic confirmation, treatment and care and further management.
Repeat screening: Re-screening in the same population at a given interval.
Risk group: Any group of people in which the prevalence or incidence of TB is significantly higher than in the general population.
Screening test, examination or procedure for TB: Used to distinguish people with a high likelihood of having TB disease from people who are highly unlikely to have TB. A screening test is not intended to be diagnostic. People with positive results on a screening test should undergo further evaluation, depending on the screening algorithm used.
Systematic screening for TB disease: Systematic identification of people at risk for TB disease in a predetermined target group by assessing symptoms and using tests, examinations or other procedures that can be applied rapidly. For those who screen positive, the diagnosis needs to be established by one or several diagnostic tests and additional clinical assessments. This term is sometimes used interchangeably with “active tuberculosis case finding”. It should be distinguished from testing for TB infection (with a TB skin test or interferon-g release assay).
Triage: The process of deciding the diagnostic and care pathways for people, based on their symptoms, signs, risk markers, and test results. Triaging involves assessing the likelihood of various differential diagnoses as a basis for making clinical decisions. It can follow more-or-less standardized protocols and algorithms and may be done in multiple steps.
Triage test for TB: A test that can be conducted rapidly in people presenting to a health facility to differentiate those who should undergo further diagnostic evaluation for TB from those who should undergo other further investigation for non-TB diagnoses.
Tuberculosis (TB): The disease state caused by Mycobacterium tuberculosis. It is usually characterized by clinical manifestations, which distinguishes it from TB infection without signs or symptoms. In this document, it is referred to simply as “TB” or “TB disease”. It should be distinguished from “TB infection” (previously referred to as “latent TB infection” or LTBI, a term that incorporated generations of TB bacilli that are not dormant). Pulmonary TB involves the lungs and is the most common form of TB. Extrapulmonary TB involves organs other than the lungs (e.g. pleura, lymph nodes, abdomen, genitourinary tract, skin, joints and bones or meninges). The two forms may coexist in the same patient.
Tuberculosis preventive treatment: Treatment offered to individuals considered to be at risk of TB disease in order to reduce that risk. Also referred to as “treatment of TB infection” and previously treatment of “latent TB infection”.
WHO four-symptom screen: The presence of either cough, fever, weight loss or night sweats used as a screening test in people living with HIV.