Definitions

Drug-susceptible TB: TB disease with no evidence of infection with a strain of Mycobacterium tuberculosis complex that is resistant to rifampicin or isoniazid (1). This includes people for whom drug susceptibility testing was not done or for whom drug susceptibility testing shows a strain of M. tuberculosis complex that is susceptible to both rifampicin and isoniazid.

Extrapulmonary TB: TB disease involving organs other than the lung parenchyma or tracheobronchial tree (e.g. pleura, lymph nodes, digestive track, genitourinary tract, skin, joints and bones, or meninges) (1).

Food assistance: A broad range of interventions that increase the options for households to access food, regardless of nutritional status. Examples include direct food provision, cash-based transfers, food vouchers and connection to broader social protection programmes.

Food insecurity: Lack of regular access to enough safe and nutritious food for normal growth and development, and an active and healthy life. This may be due to unavailability of food or lack of resources to obtain food (2).

High energy–protein food: Food that aims to boost intake of energy and protein. This may include specially formulated food such as biscuits or shakes, or locally manufactured food.

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

Household of a person with TB: For the purposes of this guideline, a household where at least one member has been diagnosed with TB. This term also includes the person with TB.

Malnutrition: Deficiencies or excesses in nutrient intake, imbalance of essential nutrients or impaired use of nutrients. The double burden of malnutrition comprises both undernutrition and overweight and obesity, as well as micronutrient deficiencies and diet-related noncommunicable diseases (4).

Micronutrients: Vitamins and minerals needed by the body in very small amounts. They enable the body to produce enzymes, hormones and other substances that are essential for proper growth and development (5).

Mild undernutrition¹ (otherwise referred to as mild thinness in adults): Defined as a body mass index (BMI) of 17.00–18.49 kg/m² (6). This term is not used for infants, children or adolescents.

Moderate undernutrition² (commonly referred to as moderate acute malnutrition in children, and moderate thinness in adults):

  • In infants and children aged below 5 years, this is defined as moderate wasting; that is, a weight-for-height Z-score or weight-for-length Z-score between –3 standard deviations (SD) and less than –2 SD (≥ –3 SD to < –2 SD) and/or a mid-upper arm circumference (MUAC) of between 115 mm and less than 125 mm (≥115 to <125 mm), and no nutritional oedema (7).
  • In children and adolescents aged 5–19 years, a BMI-for-age-and-sex Z-score between –3 SD and less than –2 SD (≥ –3 SD to < –2 SD) (6).
  • In adults aged over 19 years, a BMI of 16.00–16.99 kg/m² (6).

Multidrug-resistant TB: TB disease caused by a strain of M. tuberculosis complex that is resistant to both rifampicin and isoniazid (1).

Multiple micronutrients: In this document, a single administration of two or more micronutrients.

Nutritional assessment: An assessment that allows health care providers to systematically evaluate the overall nutritional status of individuals, diagnose malnutrition, identify underlying pathologies that lead to malnutrition and plan necessary interventions (8).

Nutritional intervention: In this document, purposeful actions that are intended to increase macronutrient intake and improve the nutritional or clinical status of an individual. Examples include direct food provision, specially formulated foods, cash-based transfers and food vouchers. Although broadly recognized as a nutritional intervention, the provision of micronutrients is addressed separately in this guideline.

Pulmonary TB: TB disease involving the lung parenchyma or the tracheobronchial tree (1). Note: A case with both pulmonary and extrapulmonary TB should be recorded and counted as a case of pulmonary TB for surveillance purposes.

Severe undernutrition² (commonly referred to as severe acute malnutrition in children and severe thinness in adults):

  • In infants and children aged below 5 years, defined as nutritional oedema and/or severe wasting; that is, a weight-for-height Z-score or weight-for-length Z-score of less than –3 SD and/or a MUAC of less than 115 mm (7).
  • In children and adolescents aged 5–19 years, a BMI-for-age-and-sex Z-score of less than –3 SD (6).
  • In adults aged over 19 years, a BMI of less than 16 kg/m² (6).

Specially formulated foods: Foods that have been specifically designed, manufactured, distributed and used according to Codex Alimentarius for either special medical purposes (9) or special dietary uses (10) (e.g. ready to use therapeutic foods [RUTF], used to treat children with severe acute malnutrition; ready to use supplementary foods [RUSF], and fortified blended foods – used to supplement children with moderate acute malnutrition).

Stunting: Length-for-age or height-for-age Z-score of less than –2 SD according to the World Health Organization child growth standards (11).

Tuberculosis (TB): The disease state caused by M. tuberculosis complex. Also referred to as TB “disease” to distinguish it from TB infection (1). The term TB refers to all forms and includes pulmonary TB, extrapulmonary TB, drug-susceptible TB and drug-resistant TB.

Tuberculosis infection: A state of persistent immune response to stimulation by M. tuberculosis antigens with no evidence of clinically manifest active TB disease. Most infected people have no signs or symptoms of TB but are at risk for TB disease. This was previously referred to as “latent TB infection”; however, because infection cannot always be considered latent, the term TB infection is now used instead. There is no gold standard test for direct identification of M. tuberculosis infection in humans (3).

Undernutrition: Includes wasting (low weight-for-height and/or nutritional oedema), stunting (low height-for-age) and underweight (low weight-for-age or low BMI-for-age or low BMI) and micronutrient deficiencies (4, 7). In this document, “undernourished” refers to the state of undernutrition.

Underweight:

  • In infants, children and adolescents aged up to 19 years, a weight-for-age Z-score of less than –2 SD (4).
  • In adults, a BMI of less than 18.5 kg/m² (12).

References for definitions³

  1. WHO consolidated guidance on tuberculosis data generation and use. Module 1. Tuberculosis surveillance. Geneva: World Health Organization; 2024 (https://iris.who.int/handle/10665/376612). Licence: CC BY-NC-SA 3.0 IGO.
  2. Hunger and food insecurity [website]. Rome: Food and Agriculture Organization of the United Nations; 2025 (https://www.fao.org/hunger/en).
  3. WHO consolidated guidelines on tuberculosis. Module 1: prevention – tuberculosis preventive treatment, second edition. Geneva: World Health Organization; 2024 (https://iris.who.int/handle/10665/378536). Licence: CC BY-NC-SA 3.0 IGO.
  4. Malnutrition [website]. Geneva: World Health Organization; 2025 (https://www.who.int/health-topics/malnutrition#tab=tab_1).
  5. Micronutrients [website]. Geneva: World Health Organization; 2024 (https://www.who.int/health-topics/micronutrients#tab=tab_1).
  6. IMAI district clinician manual: hospital care for adolescents and adults: guidelines for the management of illnesses with limited-resources. Geneva: World Health Organization; 2012 (https://iris.who.int/handle/10665/77751).
  7. WHO guideline on the prevention and management of wasting and nutritional oedema (acute malnutrition) in infants and children under 5 years. Geneva: World Health Organization; 2023 (https://iris.who.int/handle/10665/376075). Licence: CC BY-NC-SA 3.0 IGO.
  8. Kesari A, Noel JY. Nutritional assessment. Treasure Island (FL): 2024 (https://www.ncbi.nlm.nih.gov/pubmed/35593821). Licence: StatPearls.
  9. Food and Agriculture Organization of the United Nations, World Health Organization. Standard for the labelling of and claims for foods for special medical purposes CODEX STAN 180-1991. Rome: Food and Agriculture Organization of the United Nations; 1991 (https://www.fao.org/fao-who-codexalimentarius/sh-proxy/ar/?lnk=1&url=https%253A%252F%252Fworkspace.fao.org%252Fsites%252Fcodex%252FStandards%252FCXS%2B180-1991%252FCXS_180e.pdf).
  10. Food and Agriculture Organization of the United Nations, World Health Organization. General standard for the labelling of and claims for prepackaged foods for special dietary uses CODEX STAN 146-1985. Rome: Food and Agriculture Organization of the United Nations; 1985 (https://www.fao.org/4/y2770e/y2770e04.htm).
  11. Child malnutrition: stunting among children under 5 years of age [website]. Geneva: The Global Health Observatory, World Health Organization; 2025 (https://www.who.int/data/gho/indicator-metadata-registry/imr-details/72).
  12. Physical status: the use of and interpretation of anthropometry, report of a WHO expert committee. Geneva: World Health Organization; 1995 (https://iris.who.int/handle/10665/37003).

1 The word “undernutrition” has been used in the interest of uniformity of language across populations.
2 The word “undernutrition” has been used in the interest of uniformity of language across populations.
3 All references were accessed on 7 May 2025.

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