accuracy estimates due to methodological flaws and heterogeneity in study reference standards [66]. Variability in sensitivity of POCUS signs for PTB found in the systematic review may imply operator dependence, a weakness that has been identified by other authors [67]. Additionally, image acquisition and image analysis protocols have not been clearly defined for POCUS for PTB [66], unlike the FASH protocol for EPTB [62]. In summary, additional optimisation and evaluation are needed to assess the potential use of POCUS for TB, especially among children and other populations where conventional tests are likely to underperform. Conclusion The use of imaging to aid the diagnosis of TB has a long and varied history. CXR is currently recommended by the WHO in several different use cases for the prevention and diagnosis of TB, but CXR access is limited in many low-resource, high-TB-burden settings. Recent developments in portable and ultra-portable digital CXR systems have the potential to substantially widen access to imaging for TB, but the high cost of hardware is a concern for scale-up in low-resource settings. The development of more affordable digital X-ray systems could greatly help, as X-rays are needed for diverse conditions at the primary-care level. In 2021, CAD was recommended by the WHO as an alternative to human interpretation of digital CXRs and also has the potential to widen access to imaging for TB. However, the neural networks underlying these CAD products reach decisions through opaque processes, and the rapid speed of product development creates programmatic challenges for their use. Lack of evidence on CAD for use in children is a key evidence gap that must be addressed. The recent introduction of a validation platform that performs independent analysis of AI-based diagnostic products will strengthen global systems for the evaluation of CAD products, as will the upcoming WHO prequalification technical specification for these products. POCUS is much less expensive than CXR but is not as validated as CXR for TB. POCUS has moderate diagnostic accuracy for EPTB, while the current evidence base for POCUS for PTB is limited and of poor quality. Additional optimisation and evaluation are needed for POCUS as a screening test for TB. References 1 Williams FH. Some of the medical uses of the Roentgen rays. Br Med J 1898 1: 1006–1007. 2 WHO. WHO Expert Committee on Tuberculosis: Ninth Report. Geneva, WHO, 1974. 3 Harries AD, Maher D, Nunn P. An approach to the problems of diagnosing and treating adult smear-negative pulmonary tuberculosis in high-HIV-prevalence settings in sub-Saharan Africa. Bull World Health Organ 1998 76: 651–662. 4 WHO. Improving the Diagnosis and Treatment of Smear-negative Pulmonary and Extrapulmonary Tuberculosis Among Adults and adolescents: Recommendations for HIV-prevalent and Resource-constrained Settings. Geneva, WHO, 2007. 5 Miller C, Lonnroth K, Sotgiu G, et al. The long and winding road of chest radiography for tuberculosis detection. Eur Respir J 2017 49: 1700364. 6 Ahmad Khan F, Pande T, Tessema B, et al. Computer-aided reading of tuberculosis chest radiography: moving the research agenda forward to inform policy. Eur Respir J 2017 50: 1700953. 7 Naufal F, Chaisson LH, Robsky KO, et al. Number needed to screen for TB in clinical, structural or occupational risk groups. Int J Tuberc Lung Dis 2022 26: 500–508. 8 Robsky KO, Chaisson LH, Naufal F, et al. Number needed to screen for tuberculosis disease among children: a systematic review. Pediatrics 2023 151: e2022059189. 9 WHO. WHO Consolidated Guidelines on Tuberculosis: Module 2: Screening – Systematic Screening for Tuberculosis Disease. Geneva, WHO, 2021. 10 Berteloot L, Marcy O, Nguyen B, et al. Value of chest X-ray in TB diagnosis in HIV-infected children living in resource-limited countries: the ANRS 12229-PAANTHER 01 study. Int J Tuberc Lung Dis 2018 22: 844–850. 11 Drain PK, Bajema KL, Dowdy D, et al. Incipient and subclinical tuberculosis: a clinical review of early stages and progression of infection. Clin Microbiol Rev 2018 31: e00021-18. 86 https://doi.org/10.1183/2312508X.10024322 ERS MONOGRAPH |THE CHALLENGE OF TB IN THE 21ST CENTURY