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Systematic Screening for Active Tuberculosis: Principles and Recommendations. Geneva: World Health Organization; 2013.

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Systematic Screening for Active Tuberculosis: Principles and Recommendations.

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Executive summary

Purpose of the guideline

The purpose of this document is to provide evidence-based:

  • key principles to guide the planning and implementation of systematic screening for active tuberculosis (TB);
  • recommendations on prioritizing risk groups for systematic screening for active TB; and
  • algorithm options for screening and diagnosis of active TB.

The target audience for the guide is principally staff at national TB programmes and other public-health agencies, as well as other public and private partners involved in planning, implementing and monitoring TB-control activities in countries with an intermediate-to-high burden of TB.

Definition of systematic screening for active TB

For the purpose of this guideline, systematic screening for active TB is defined as the systematic identification of people with suspected active TB, in a predetermined target group, using tests, examinations or other procedures that can be applied rapidly. The screening tests, examinations or other procedures should efficiently distinguish people with a high probability of having active TB from those who are unlikely to have active TB. Among those whose screening is positive, the diagnosis needs to be established by one or several diagnostic tests and additional clinical assessments, which together have high accuracy.

Systematic screening for active TB is predominantly provider-initiated. It may target people who do not seek health care because they do not have or recognize symptoms, because they do not perceive that they have a health problem that warrants medical attention, because 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 and people with diabetes mellitus) who may seek care for reasons other than symptoms compatible with TB.

Objectives of systematic screening for active TB

The primary objective of screening for active TB is to ensure that active TB is detected early and treatment is initiated promptly, with the ultimate aim of reducing the risk of poor treatment outcomes, health sequelae and the adverse social and economic consequences of TB, as well as helping to reduce TB transmission.

Reviews of the evidence

In order to develop the principles and recommendations for systematic screening for active TB, WHO established a Guideline Development Group (see Section 4 for information on the guideline development process) and commissioned four systematic reviews (summarized in Section 5; the full reviews can be found under the link “Systematic reviews and PICO questions” available at www.who.int/tb/tbscreening), covering:

  • the general benefits of TB screening (Review 1);
  • the sensitivity and specificity of different TB screening tools and algorithms (Review 2);
  • the number needed to screen to detect one case of active TB in different risk groups (Review 3);
  • the acceptability of TB screening in different risk groups (Review 4).

The burden of undetected TB is high in many settings, especially in some risk groups. The delay in diagnosing TB and initiating appropriate treatment is often long, especially in groups with poor access to health care. Many people with active TB do not experience typical TB symptoms in the early stages of the disease. These individuals are unlikely to seek care early, and may not be properly diagnosed when seeking care. Passive case-finding therefore leads to missed or delayed diagnoses for many people. Appropriately diagnosing and treating TB dramatically improves health outcomes when compared with not diagnosing and treating the disease. These observations together constitute indirect evidence that screening for active TB in selected risk groups should benefit individuals and public health.

However, while the systematic reviews show that there is some evidence that screening can improve the early detection of TB, the direct evidence remains weak for the impact of screening on health outcomes and TB transmission when compared with passive case-finding alone. Furthermore, data are lacking on the cost effectiveness of screening compared with other interventions to improve early detection, and it is clear that indiscriminate screening can require a lot of resources.

Therefore, indiscriminate mass screening should be avoided; and screening in selected risk groups requires careful consideration of the potential benefits and risks of harm, including side effects and other harms for the individual from false diagnosis as well as the inappropriate use of health-care resources.

Decisions on when and how to screen for active TB, which risk groups to prioritize and which algorithm to use for screening and diagnosis depend on the epidemiological situation, the capacity of the health system, and the availability of resources.

Key principles for systematic screening for active TB

The following key principles should be considered when planning a TB-screening initiative.

  1. Before screening is initiated, high-quality TB diagnosis, treatment, care, management and support for patients should be in place, and there should be the capacity to scale these up further to match the anticipated rise in case detection that may occur as a result of screening. In addition, a baseline analysis should be completed in order to demonstrate that the potential benefits of screening clearly outweigh the risks of doing harm, and that the required investments in screening are reasonable in relation to the expected benefits.
  2. Indiscriminate mass screening should be avoided. The prioritization of risk groups for screening should be based on assessments made for each risk group of the potential benefits and harms, the feasibility of the initiative, the acceptability of the approach, the number needed to screen, and the cost effectiveness of screening.
  3. The choice of algorithm for screening and diagnosis should be based on an assessment of the accuracy of the algorithm for each risk group considered, as well as the availability, feasibility and cost of the tests.
  4. TB screening should follow established ethical principles for screening for infectious diseases, observe human rights, and be designed to minimize the risk of discomfort, pain, stigma and discrimination.
  5. The TB screening approach should be developed and implemented in a way that optimizes synergies with the delivery of other health services and social services.
  6. A screening strategy should be monitored and reassessed continually to inform re-prioritization of risk groups, re-adaptation of screening approaches when necessary and discontinuation of screening at an appropriate time.

Details on the key principles are provided in Section 7.

Recommendations on risk groups to screen

Seven recommendations on prioritizing risk groups for screening have been developed. The recommendations are divided into strong recommendations and conditional recommendations.

A strong recommendation is one for which the desirable effects of adhering to the recommendation are judged to clearly outweigh the undesirable effects, and for which screening is judged to be feasible, acceptable and affordable in all settings.

A conditional recommendation is one for which the desirable effects of adhering to the recommendation probably outweigh the undesirable effects but the trade-offs, cost effectiveness, feasibility or affordability, or some combination of these, are uncertain. Reasons for uncertainty may include:

  • a lack of high-quality evidence to support the recommendation;
  • evidence of limited benefits from implementing the recommendation;
  • high costs or low feasibility or acceptability, or a combination of these.

Recommendations have not been developed for all of the risk groups initially considered due to a lack of evidence; in particular in Review 1 (the systematic review of the general benefits of screening) there was a lack of studies assessing outcomes judged to be critical for several risk groups (see Sections 4.2 and 5). Additional risk groups may be considered for screening based on the criteria set out in the key principles in Section 7.

The recommendations are listed below. For details on the evidence, see Section 5 and Annex I in this document, and supporting at www.who.int/tb/tbscreening. See Section 8 in this document for remarks on each recommendation.

Strong recommendations

Recommendation 1: Household contacts and other close contacts should be systematically screened for active TB.

Recommendation 2: People living with HIV should be systematically screened for active TB at each visit to a health facility.

Recommendation 3: Current and former workers in workplaces with silica exposure should be systematically screened for active TB.

Conditional recommendations

Recommendation 4: Systematic screening for active TB should be considered in prisons and other penitentiary institutions.

Recommendation 5: Systematic screening for active TB should be considered in people with an untreated fibrotic chest X-ray lesion.

Recommendation 6: In settings where the TB prevalence in the general population is 100/100 000 population or higher, systematic screening for active TB should be considered among people who are seeking health care or who are in health care and who belong to selected risk groups. (The risk groups to be considered are listed in the remarks to this recommendation in Section 8).

Recommendation 7:

  1. Systematic screening for active TB may be considered for geographically defined subpopulations with extremely high levels of undetected TB (1% prevalence or higher).
  2. Systematic screening for active TB may be considered also for other subpopulations that have very poor access to health care, such as people living in urban slums, homeless people, people living in remote areas with poor access to health care, and other vulnerable or marginalized groups including some indigenous populations, migrants and refugees.

Algorithms for screening and diagnosis

Different screening algorithm options have been developed for adults and children. (See Section 5.2 for a summary of the evidence, Section 9 for remarks on each algorithm, and Annex II and Annex III in this document, as well as supporting material available at www.who.int/tb/tbscreening for details on the accuracy of different tests, the flow charts of the algorithms and the modelled yield for each algorithm for adults.)

Options for the initial screening include screening for symptoms (screening either for cough lasting for longer than 2 weeks, or screening for any symptom compatible with TB, including cough of any duration, haemoptysis, weight loss, fever or night sweats) or screening with chest radiography. If symptom screening is used initially, then chest radiography can be used as a second screen to improve the pretest probability of the subsequent diagnostic test, and to reduce the number of people who need to undergo further diagnostic evaluation.

As part of the initial screening, each algorithm includes steps to identify people living with HIV; these persons should be screened and diagnosed by following the algorithm for people living with HIV in Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy for people living with HIV in resource-constrained settings.10 Screening can therefore be enhanced by combining screening for TB with screening for HIV.

Each algorithm for adults includes options for the initial diagnostic testing of people whose screening test is positive: either sputum-smear microscopyi or a rapid molecular test that has been demonstrated to have high accuracy for both smear-positive and smear-negative pulmonary TB, such as the Xpert MTB/RIF test (Cepheid, Sunnyvale, CA) (or any rapid test recommended by WHO in the future and that has the same or better accuracy). Positive or negative diagnostic results may require a repeat test or further diagnostic evaluation using culture, drug-susceptibility testing, clinical assessment, or some combination of these. Culture is the gold standard of diagnostic testing for TB. However, in these algorithms it is not considered for use as an initial diagnostic test because it demands more resources and requires a much longer wait for results (2–6 weeks) than both the Xpert MTB/RIF test and sputum-smear microscopy, both of which can provide final test results in less than 1 day. Where resources permit, and where the health system has sufficient capacity to ensure that patients are followed up after culture results are available, culture may be used in parallel with or after testing with the Xpert MTB/RIF or sputum-smear microscopy. Culture with drug-susceptibility testing should be done according to guidelines for diagnosing drug-resistant TB.16

The algorithms have been developed predominantly to detect pulmonary TB. The accuracy of tests for screening and diagnosis has been assessed using culture-confirmed pulmonary TB as the gold standard.

The algorithms all have different sensitivity and specificity (see Section 5.2), and therefore different yields of true-positive and true-negative cases and false-positive and false-negative TB. Yields also vary with TB prevalence in the screened population. For all algorithms, the risk of a false-positive diagnosis increases as the prevalence declines; therefore, special attention must be paid to diagnostic accuracy, particularly when the prevalence of TB in the screened population is less than 1%.

The algorithms have different costs, and requirements in terms of human resources and health systems. The choice of algorithm for screening and diagnosis depends on the risk group, the prevalence of TB, the availability of resources and feasibility. See Section 8 for remarks about choosing an appropriate algorithm for different risk groups.

The algorithms are described below.

Screening in adults and children aged 10 years or older

Option 1: This algorithm includes an interview about TB symptoms and HIV status. All people with cough lasting longer than 2 weeks should be investigated for TB. Chest radiography should be considered as a second screening for people who have had cough lasting longer than 2 weeks; people with an abnormal chest radiograph suggestive of TBii should be evaluated for TB. For people known to be HIV-positive, see the Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy for people living with HIV in resource-constrained settings.10

Option 2: This algorithm includes an interview about TB symptoms and HIV status. Further investigation for TB should be done for persons with any of the following symptoms: cough of any duration, haemoptysis, weight loss, fever or night sweats. Chest radiography should be considered as a second screening for people who screened positive when asked about symptoms; and people with an abnormal chest radiograph suggestive of TB should be evaluated for TB. For persons known to be HIV-positive, see the Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy for people living with HIV in resource-constrained settings.10

Option 3: This algorithm includes chest radiography and an interview about HIV status. Persons with an abnormal chest radiograph suggestive of TB should be evaluated for TB. For persons known to be HIV-positive, see the Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy for people living with HIV in resource-constrained settings.10

Screening in children aged younger than 10 years

Screening children who are living with HIV or who are contacts of someone with TB

  • For children who are living with HIV or who are contacts of someone with TB, symptom-based screening should be done to identify those with cough, fever, weight loss or fatigue of any duration; children with any symptom should be investigated for TB.
  • For children who are living with HIV or who are contacts of someone with TB, chest radiography may be added to the initial screening. Children with any symptom or a chest radiograph with an abnormality suggestive of TB should be investigated for TB.

Screening children in situations other than as part of contact investigation or screening among people living with HIV

  • For children who are younger than 10 years and who are screened in situations other than as part of contact investigation or screening for people living with HIV, an interview should be done to determine whether the child is known to be HIV-positive or has had recent contact with someone who has TB, in either case the algorithm options for children younger than 10 years who are living with HIV or who are contacts of someone with TB apply.

Footnotes

i

This refers to conventional light microscopy used to examine direct smears stained with Ziehl–Neelsen (with or without specific sputum-processing methods) or fluorescence microscopy (including microscopy with light-emitting diodes).

ii

Chest radiographs suggestive of TB may be separated into those that are suggestive of active TB, and those that are suggestive of either active or inactive TB (see Section 9 for details).

Copyright © World Health Organization 2013.

All rights reserved. Publications of the World Health Organization are available on the WHO web site (www.who.int) or can be purchased from WHO Press, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland (tel.: +41 22 791 3264; fax: +41 22 791 4857; e-mail: tni.ohw@sredrokoob).

Requests for permission to reproduce or translate WHO publications –whether for sale or for non-commercial distribution– should be addressed to WHO Press through the WHO web site www.who.int/about/licensing/copyright_form/en/index.html).

Bookshelf ID: NBK294091

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