Speed and accuracy of case detection are critical success factors in the fight against TB. Deaths caused by TB worldwide are estimated at 1.7 million people per year and about 40% of TB cases are not detected. If TB is detected early and treated, patients quickly become non-infectious and eventually cured. With a timely check for TB, an accurate diagnosis and treatment, TB can be controlled and diminished. Digital Chest X-ray innovations have the potential to help respond to this need.

In many countries the lack of early and accurate case detection methods is a major obstacle to TB control. Sputum smear is the mainstay of diagnosis in most resource-poor countries, but this misses at times more than 50% of the cases. Utility of routine sputum microscopy was further diminished by the HIV epidemic as smear-negative TB is more frequent. This is particularly a problem in sub-Saharan Africa. New screening and diagnostic technologies need to be more sensitive, faster in yielding results and/or simpler to use than sputum microscopy.

Improved technologies that can shorten the diagnostic process and facilitate early detection will decrease morbidity, improve treatment outcomes and interrupt the transmission of TB. Chest X-ray (CXR) is widely established in TB prevention programmes in especially the western world, Asia and eastern Europe, but numerous factors complicate its use in low and medium resource countries.

Current situation

Currently sputum microscopy (more than 100 years old technique) is widely used to detect TB, however the sensitivity can be low (50-60%) and test results are not immediately available. Culture is highly accurate but takes 6-8 weeks to have results available and requires adequate laboratory facilities. Recent developments, notably increasing rates of smear-negative tuberculosis in countries with HIV epidemics, have convinced leading authorities that the use of CXR earlier in the decision tree should become a priority in the fight against TB.

In many low resource areas analogue radiology using films is available though not in all health facilities. The challenges of this technique are the need to have chemicals and a dark room to develop films and to have the expertise on site to read the Chest X-Ray (CXR). Often images are of poor quality and readability and as such hinder the diagnostic process. Experienced clinicians to perform high quality reading might not be available. Innovations in the area of digital radiology and image compressing are therefore welcomed by leading health institutions as effective new solutions to old problems in detecting TB suspects.

Digital innovations

Digital radiology simplifies the creation of a quality image to 2 mouse clicks provided staff is correctly trained. Images are instantly available and can be diagnosed on distance using the internet or even mobile phone network connections. In addition, the experts on the development of Computer Aided Diagnosis of digital images (CAD4TB) expect the sensitivity of digital CXR with CAD4TB to reach 90%. Only after thousands of digital images have been interpreted in the same systematic way (including sputum microscopy and culture), CAD4TB experts expect specificity of chest images to rise from 50 to 80%. The targetted “jump” of CXR speed and accuracy [ (sensitivity + specificity)/2 ] is illustrated in the below graph.

New rapid tests

Case detection in children

It is more difficult to diagnose TB in children than in adults as they are less likely to have the classical signs and symptoms of the disease, like couch. Children have usually less bacilli in the sputum and the younger children can not produce a sample for microscopy. Therefore CXR plays an important role in TB diagnosis in children.