Adding digital chest x-ray screening to symptom-based screening for tuberculosis (TB) doubles the number of detecting hitherto undiagnosed TB cases compared to just symptom-based screening, suggests a recent study from South Africa reported in the Annals of the American Thoracic Society.¹

This study included 3576 adult inmates, aged 34 years (mean), from four correctional facilities in South Africa. Most of them were male, and around 16% were HIV-positive. They were evaluated for TB based on symptoms and digital chest x-ray. Two sputum samples were collected from any person who had more than one symptom suggestive of TB or computer-aided detection (CAD)>50, for liquid culture and GeneXpert MTB/RIF Ultra testing. Samples were also collected from 800 persons who had no symptoms and CAD<50. CAD uses computer programs to detect abnormalities on chest x-rays compatible with TB.

Of those screened, 24.2% required investigation, with 11.2% symptomatic, 19.1% on abnormal CAD and 24.2% with either. Sputum samples were collected from 86.2% of study subjects. Twenty-eight new TB cases (7.8 TB cases per 1,000 population) were diagnosed. Five new cases were diagnosed among the 800 participants with no symptoms. As per the authors, “based on hypothesized screening modalities, yield would have been 3.6 per 1,000 population on symptoms alone and 7.0 per 1,000 population on d-CXR alone”. Culture and Xpert Ultra testing were comparable with regard to the rates of TB diagnosis; 4.8 vs 5.6 per 1000 population, respectively.

India has the highest burden of TB and set itself a target of ending TB by 2025. However, according to the new Global Tuberculosis Report 2021, India accounted for the total global drop of 1.3 million. This has been attributed to the disruption in healthcare services during the ongoing Covid-19 pandemic. “Diagnosis and treatment of TB among key populations, including inmates within correctional facilities, is important for TB elimination”. This study suggests that digital chest x-ray as a screening modality works complementary to screening for TB based on symptoms. It increases the accuracy of diagnosis by potentially eliminating the element of subjectivity when reporting symptoms.

Reference

1. Velen K, et al. Digital chest X-ray with computer-aided detection for TB screening within correctional facilities. Ann Am Thorac Soc. 2021 Dec 16. doi: 10.1513/AnnalsATS.202103-380OC.