"The WHO policy says that Gene Xpert should be number-one choice for TB diagnostics if affordable. If we cannot afford it then priority for doing Gene Xpert goes to anyone at risk of MDR-TB or people living with HIV (PLHIV)."
10 million Gene Xpert tests have been done globally with South Africa accounting for half of them. India is increasingly doing Gene Xpert tests. Private sector did over 100,000 Gene Xpert tests. Public health sector has 119 Gene Xpert machines under RNTCP and there are plans to buy another 300! "We did a Cochrane systematic review on Gene Xpert and found that compared to 'culture test' (which is a gold standard WHO approved test), Gene Xpert picks up about 88% of TB. Even if smear is negative, Gene Xpert picks up 70% cases of TB. So that is the advantage"emphasized Dr Pai.
"In a study published in The Lancet, Gene Xpert shows good sensitivity of 62% and specificity of 98% in samples of paediatric induced sputum or expectorate. With gastric juise aspiration Gene Xpert picks up 66% of all TB in children. This is an important finding because in children sputum smear microscopy is rarely positive as it is so difficult to get sputum samples from them."
Dr Pai shared that "One of the largest studies getting published soon has assessed 115,000 Gene Xpert tests done in 18 districts of India. Gene Xpert tests were done on all patients with presumptive TB. Researchers did not wait till the end of first-line anti-TB therapy to do DST. This is not RNTCP policy yet to do DST on 'day-1' when a patient contacts a health system with presumptive TB, but researchers did it to show what will happen if we do DST right at the start of diagnostic process. Results are very impressive with 39% increase in notification rates of bacteriologically-confirmed TB and five fold increase in rifampicin resistance case detection." Rifampicin-resistance case detection has increased eight fold in Mumbai with introduction of Gene Xpert upfront testing. So when we test for drug resistance we find more than we had estimated for!
Continuum of care is important
If we diagnose more drug-resistant TB then it makes public health sense only if all the confirmed cases of drug-resistant TB get treated by sensitive drugs. It is a widely known fact that cost of treating drug-resistant TB is hundreds of times more than what it costs to treat drug-sensitive TB!
So as number of those who are getting diagnosed shoots up, drug supplies and other logistical and programmatic preparations have to be in place to ensure continuum of care. "This is the irony as MDR-TB treatment alone could account for 40% of RNTCP budget. So drug supply has to match diagnostic potential. That is why Government of India is being careful of how they roll the technology."
Diagnosing Extra-Pulmonary TB (EPTB) remains a daunting task