The Role of GeneXpert in Bacterial Diagnosis of Spinal Tuberculosis

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India has the maximum burden of tuberculosis (TB) in the world. In 2014, there were an estimated 9.6 million incident cases of TB (range, 9.1 million–10.0 million) globally, equivalent to 133 cases per 100000 population. Most of the estimated number of cases in 2014 occurred in Asia (58%) and the African Region (28%). India, Indonesia, and China alone accounted for a combined total of 43% of global cases in 2014. There were 480000 (range, 360000–600000) new cases of MDR-TB worldwide in 2014. This total includes cases of primary and acquired MDR-TB. Globally in 2014, there were an estimated 3.3% of new cases and 20% of previously treated cases with MDR-TB while estimate in India was 2.2% for new MDR-TB cases and 15% for previously treated cases with MDR-TB.
Skeletal involvement occurs in approximately 10% of all patients with extra-pulmonary TB among them spinal involvement was most common. Multidrug resistant TB (MDR-TB) of the spine is not well reported in the literature (2 case series and 6 case reports), but the number of cases detected are on rise. Increasing use of molecular diagnostics to detect MDR-TB, their growing importance in detection of TB patients with MDR-TB and effective data surveillance are reasons for detection of MDR-TB. Drug sensitivity reporting (DST) for tuberculosis spondylitis is not routinely undertaken in resource-limited countries; generally patients are treated with a standardized or empiric regimen, without the assessment of drug susceptibility. This standard of care may potentially miss drug resistance and lead to delay in diagnosis of drug resistance if any and initiation of proper treatment.
The current treatment protocol is to do DST smear microscopy and histopathology on surgically obtained sample and then initiate TB treatment. Only if the patient has clinical deterioration, Gene-Xpert is done to provide information on possible drug resistance. Gold standard at present in BJGMC for diagnosis includes either culture and/or histopathology confirmation of TB.
As many of the patients referred to this tertiary care center from peripheral centers they are already taking either ant tubercular drugs or ciprofloxacin or other antibiotics for variable period. This may affect the results of liquid culture. As Gene Xpert detects dead bacilli also, we expect it to perform better in this complicated scenario.
In a study funded by the Fogarty International Center, we propose to examine the role of GeneXpert in improving the yield of microbiologically confirmed TB and assess how many additional cases of MDR-TB are diagnosed among suspected spinal TB patients treated at a tertiary hospital in Pune, India.

Amit Kale, BJGMC Fogarty Scholar