A prospective study evaluating the impact of cartridge-based nucleic acid amplification test (CBNAAT) on the management of tuberculosis in a low-resource high-burden Indian rural setting

Background: The cartridge-based nucleic acid amplification test (CBNAAT) Xpert MTB/RIF is more sensitive than smear microscopy for the diagnosis of tuberculosis (TB). It is also more expensive, costing 1450 INR as compared to 10 INR per smear. Objectives: We conducted a prospective study to evaluate the impact of CBNAAT results on patient management in our low-resource, high-burden Indian rural setting. Materials and Method: Between February and July 2017, clinicians were asked to complete one questionnaire at the time of CBNAAT request and another when reviewing the result. The first questionnaire, “Form 1,” concerned pretest treatment status and asked clinicians to rate their confidence in the diagnosis. “Form 2” concerned postresult treatment and investigation plan. Results: Over the study period, 206 CBNAATs were requested. Form 1 was not completed for 85 patients and 21 were excluded leaving 100 in the main analysis. MTB was detected (MTB-D) in 60 of 100 (60%) of samples tested. At the time of CBNAAT request, 56 of 100 (56%) of patients were already on treatment, this being empirical in 34 of 100 (34%). Despite this, 17 of 60 (28.3%) of MTB-D results occurred in patients not yet started on treatment. Postresult treatment status was available for 94 of 100 CBNAATs (55 MTB-D and 39 MTB-ND). Following an MTB-D result, all 17 patients not on treatment started and all 38 on so already continued. Following an MTB Not Detected (MTB-ND) result, 26 of 27 (96.3%) of patients not yet on treatment remained so, but only 2 of 12 (16.7%) already on treatment stopped. Even where the clinician's pretest confidence in TB was low, 9of 30 (30%) of CBNAAT results were MTB-D. Conclusion: In a low-resource high-burden setting, CBNAAT may have greatest impact where the clinician's pretest confidence in TB is low and empirical treatment has not been started. This is because MTB-D results will lead to appropriate initiation of treatment and MTB-ND results may enable clinicians to hold-off treatment