Note: The definitions listed below apply to the terms as used in these guidelines. They may have different meanings in other contexts.

Adolescent: A person aged 10–19 years

Adult: A person over 19 years of age

Bacteriologically confirmed TB: TB diagnosed in a biological specimen by smear microscopy, culture or a WHO-approved molecular test such as Xpert® MTB/RIF

Child: A person under 10 years of age

Contact: Any person who was exposed to a person with tuberculosis

Contact investigation: A systematic process for identifying previously undiagnosed people with TB among the contacts of an index case. Contact investigation consists of identification and prioritization and clinical evaluation. It may also include testing for LTBI to identify candidates for TB preventive treatment.

High TB transmission setting: A setting with a high frequency of individuals with undetected or undiagnosed active TB, or where infectious TB patients are present and there is a high risk of TB transmission. TB patients are most infectious when they are untreated or inadequately treated. Spread is increased by aerosol-generating procedures and by the presence of highly susceptible individuals.

Household contact: A person who shared the same enclosed living space as the index case for one or more nights or for frequent or extended daytime periods during the 3 months before the start of current treatment.

Index case (index patient) of TB: The initially identified person of any age with new or recurrent TB in a specific household or other comparable setting in which others may have been exposed. An index case is the person on which a contact investigation is centred but is not necessarily the source case.

Infant: A child under 1 year (12 months) of age

Latent tuberculosis infection (LTBI): A state of persistent immune response to stimulation by M. tuberculosis antigens with no evidence of clinically manifest active TB. This is also at times referred to as TB infection. There is no gold standard test for direct identification of M. tuberculosis infection in humans. Most infected people have no signs or symptoms of TB but are at risk for active TB disease.

People who use drugs: People who engage in the harmful or hazardous use of psychoactive substances, which could impact negatively on the user’s health, social life, resources and legal situation.

Programmatic management of tuberculosis preventive treatment (PMTPT): All coordinated activities by public and private health caregivers and the community aimed at scaling up TB preventive treatment to people who need it.

TB preventive treatment (TPT): Treatment offered to individuals who are considered at risk of TB disease in order to reduce that risk. Also referred to as treatment of TB infection, LTBI treatment or TB preventive therapy.

Tuberculosis (TB): The disease state due to M. tuberculosis. In this document, it is commonly referred to as “active” TB or TB “disease” in order to distinguish it from TB infection.

Underweight: in adults usually refers to a body mass index <18.5 and in children 10 years to a weight-for-age –2 z-scores

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