Study finds high prevalence of pre-XDR TB in patients who failed to respond to initial treatment

Mumbai: A whole genome sequencing (WBS) study of 600 tuberculosis (TB) patients, who did not respond to initial treatment, revealed that 51% had the worst form of TB infection called pre-extensively drug-resistant (pre-XDR) cases followed by multidrug-resistant tuberculosis (MDR-TB) (15.5%).
The study, which was published in the current edition of Microbiology Spectrum- an indexed journal of the American Society of Microbiology, showed taking treatment decisions for tuberculosis in the absence of full drug-susceptibility data can result in amplifying resistance and may compromise treatment outcomes.
The study included samples from across Maharashtra, including Mumbai, which has the largest TB population of the country, to identify the drug-resistance profile and mutation spectrum.
Dr Anirvan Chatterjee, co-founder and CEO, HaystackAnalytics and one of the investigator, said, “These patients, who samples were sent for WGS, were referred by the private practitioners because they were either not responding to therapy or they were rifampicin resistant or they were presumptive MDR cases. But in our analysis, we found that there is a high proportion of pre-XDR in patients who are suspected to be MDR cases.”
Whole genome sequencing is considered an advanced form of testing for TB, reveals the exact strain the patient is suffering from and that too in the shortest possible time. Compared to the traditional tests, which are based on culture reports that take up to nine weeks, the WBS report of the TB bacillus affecting the patient comes within 10 to 15 days.
The study underlined that in the absence of drug-susceptibility profile, patients are usually placed on therapy, which may contain a few drugs to which the TB strain is already resistant, and such therapy ultimately fails because of the risk of amplification of resistance. It said such practices put communities at risk of exposure to increasingly resistant TB bacteria.
The study said delays in diagnosis and an effective treatment of multidrug resistant-TB in the private sector are a cause of concern.
“From our study, we understand that once we expect the patient to be drug resistant, then for a treatment to be right, you need full information about the resistance profile, which the WBS provides. The choice of drugs that are given to a patient would depend on the drug resistance profile of the bacteria that is causing the disease for that patient,” said Dr Chatterjee.
The study concluded that the ‘one size fits all’ approach is not suitable for all TB patients. Dr Mangala Gomare, one of the authors of the study and former executive health officer in BMC said WBS would be useful for the TB programme. “Doctors need not always see how the patient is responding to the therapy. They can have the whole information about all genome sequencing and then give the medicine which should exclude any antibiotic which the patient is resistant to or the bug the patient is resistant to,” she said.