Risk Group Screening

Risk Group Screening

Systematic screening for active TB in high risk populations and prompt access to appropriate treatment are crucial to END TB. Digital chest radiography, when used as a rapid triage to select individuals for bacteriological testing, facilitates screening of large groups at low costs.

Addressing the missed cases through screening does not only have an epidemiological implication but also rises human rights and equity issues. Enhanced efforts with targeted strategies are much needed for vulnerable communities and to accelerate the national TB control efforts towards TB control and elimination. [1]

TB screening is often defined as “systematic identification of people with suspected active TB in a predetermined target group, using tests, examinations, or other procedures which can be applied rapidly and do not only target individuals seeking care for symptoms or signs”. [2]

Such TB screening algorithm will generally be composed of one or more screening methods and one or more confirmatory tests. Symptom questionnaires and chest radiography are the most available and best documented methods to screen for active TB disease. [3]. While the use of Xpert in programmatic settings has expanded in recent years, the WHO has also recommended use of more cost effective diagnostic algorithms through screening tools such as CXR [4]. Development of software that offer automated interpretation of CXRs, represents an important milestone that can link technological innovations to screening programs for tuberculosis.

Advances in digital radiology present an opportunity to overcome the barriers of using traditional film based chest X-rays with human readers for highly (cost)effective digital screening tools in low resource-high burden settings. Computer Aided Detection for TB now surpasses the performance of a trained human reader and can be used for passive and active TB case finding as well as in prevalence surveys [5].

WHO

The available evidence suggests that screening, if done in the right way and targeting the right people, may reduce suffering and death.

Knut Lönnroth, WHO - PSI/GTB UNION Liverpool, October 2016.

  • CXR alone cannot establish a diagnosis for TB – bacteriological confirmation must always be attempted
  • In absence of bacteriological confirmation, sometimes clinical diagnosis is needed
  • If patient is not critically ill, a wait-and-see approach can be used
  • WHO has no specific guidance on use of CXR in clinical diagnosis
  • Proportion of TB patients with non-confirmed TB is a possible indicator for quality control

The primary objective of systematic TB screening is early TB case detection, which requires a sensitive screening tool

  • High sensitivity of CXR for TB screening (87-98%)
    • Highly sensitive if using “any abnormality consistent with TB” as criteria for an abnormal result
    • Means the vast majority of those with TB who undergo CXR screening will have an abnormal result
  • Low specificity of CXR for TB screening (46-89%)
    • Means the test will also be abnormal in individuals with other lung abnormalities besides TB that also need to be followed up (e.g. cancer, pneumonia, emphysema) -> benefit to individual being screened
    • Also identifies individuals with inactive TB/fibrotic lesions, who are at high risk of developing active TB in future and require follow-up
    • However, means it needs to be coupled with a bacteriological test with high sensivitiy and specificty for diagnosis
  • While the preferred screening tool based on test accuracy, can be expensive and logistically challenging to use, especially in ACF (outside of health facility)

WHO recommends that priority be given to populations with:

  • High TB prevalence (risk factor profile and/or poor access/delay)
  • High risk of severe negative consequences if diagnosis is missed
  • High transmission risk

Stop TB partnership

A Paradigm Shift is needed in the way we fight TB. Unless we speak about Active Case Finding, X-ray, contacts, prevention (amongst others) we will not reach our targets.

ACF innovations to support Paradigm Shift implementation

  • Systematic screening aims to detect more cases, and to detect them early
  • Innovations in diagnostic imaging make screening in high risk groups faster and more sustainable
  • Digital Chest X-ray (dCXR) with Computer Aided Detection (CAD) as a rapid and automated triage test before Xpert® MTB/RIF can significantly reduce screening cost
  • To scale up ACF in risk groups rapid and more affordable diagnostic pathways are required
  • Relatively high cost and 2 hours processing time still limit the uptake of Xpert as point-of-care test
  • CAD4TB automatically scores chest radiographs between 0 -100 on abnormalities consistent with TB in 1 minute and surpasses trained human reader performance
  • These innovations support the Stop TB Partnership Paradigm Shift implementation through new diagnostic pathways to detect more TB cases earlier at much lower cost