The problem of underdiagnosis was underlined by South Africa's first TB prevalence survey - conducted mainly in 2018, with key findings made public in 2021. As Spotlight reported at the time, of the 234 people found to have TB in the survey, more than half - around 58% - had abnormal X-rays without any TB symptoms, 35% had both abnormal X-rays and TB symptoms, and around 7% had symptoms only.
But the challenge with the current testing system, says Connell, is that it is passive. This means that we generally still wait for patients to present themselves at health facilities once their symptoms are severe enough. Furthermore, she says, people at risk of TB and those who have any TB symptoms or a chest X-ray that suggests TB require a molecular TB test to confirm if they have TB. The test requires a quality sputum sample - which some people, especially children, struggle to produce.
In XACT 2, researchers compared TB testing with GeneXpert Edge with an older form of TB testing called Smear Microscopy . Sputum samples in the study were also tested using culture, which is much slower but extremely accurate and typically used as a point of reference in such studies. In short, he says they had to be sure that GeneXpert would comprehensively out-perform smear microscopy, especially with regard to detection of infectious patients.
"Rapid treatment initiation remains the most effective way of rendering patients non-infectious," says Dheda,"thus the main advantage of mobile testing is that the diagnosis of TB is made very early on in the course of the disease before it is spread to other individuals."One concerning finding was that only 46.5% of culture-positive study participants were on treatment 60 days after being diagnosed.