Tag Archives: Communicable Diseases

WHO releases updated guidance on systematic screening for Tuberculosis

The World Health Organization (WHO) has released updated guidance on screening for tuberculosis (TB)*. This article will briefly present the recommendations.

Background Information:

Tuberculosis disease: The disease state caused by Mycobacterium tuberculosis. It is usually characterized by clinical manifestations, which distinguish it from TB infection without signs or symptoms (previously referred to as latent TB infection). Also referred to as active tuberculosis.

Screening test, examination, or procedure for tuberculosis disease: A test, examination, or other procedure 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.

Risk groups: Any group of people in which the prevalence or incidence of TB is significantly higher than in the general population.

Systematic screening for TB disease: The 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).

Systematic screening for TB disease is predominantly provider initiated. It may be conducted among people who do not seek health care because they do not have or recognize symptoms, they do not perceive that they have a health problem that warrants medical attention, there are barriers to accessing care, or for other reasons. It may also target people seeking health care who do or do not have symptoms or signs compatible with TB and who may not be identified by passive case-finding as possibly having TB. People seeking care who may be eligible for TB screening include people with medical conditions that constitute risk factors for TB (such as people living with HIV or diabetes mellitus) who may be seeking care for reasons other than symptoms compatible with TB.

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 it may be done in multiple steps.

Triage test for TB: A test that can be rapidly conducted among people presenting to a health facility to differentiate those who should have further diagnostic evaluation for TB from those who should undergo further investigation for non-TB diagnoses.

Active (tuberculosis) case-finding (ACF): 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”.

Computer-aided detection (CAD): 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.

Enhanced (tuberculosis) case-finding: Health information or education, or awareness campaigns to provide information about what type of health-seeking behaviour is appropriate when people experience symptoms of TB; this type of case-finding may be combined with improving access to diagnostic services. Enhanced case-finding may or may not be combined with screening.

Passive 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.

WHO-recommended four-symptom screen (W4SS): cough, fever, weight loss or night sweats.

Why these guidelines?

To facilitate the implementation of TB screening at the country level, WHO published guidelines on Systematic screening for active tuberculosis: principles and recommendations in 2013. Since then, there have been important new studies evaluating the impact of screening interventions on both individual-level and community-level outcomes related to TB, as well as new research evaluating innovative tools for screening for TB – including the use of computer-aided detection of TB on digital radiographs, C-reactive protein (CRP) and molecular WHO-recommended rapid diagnostic tests for TB (mWRDs; eg Xpert MTB/RIF)– among important populations at high risk for TB disease.

In view of these new developments and due to requests by countries for more guidance, WHO convened a Guideline Development Group (GDG) in 2020 to examine the evidence and update the 2013 guidelines. The GDG met in virtual sessions between June and October 2020 and proposed several new and updated recommendations related to TB screening.

*WHO consolidated guidelines on tuberculosis. Module 2: screening – systematic screening for tuberculosis disease. Geneva: World Health Organization; 2021. Licence: CC BY-NC-SA 3.0 IGO