Abstract

Background: There is paucity of data regarding the diagnostic role of cartridge-based nucleic acid amplification test (CBNAAT), in the diagnosis of drug resistant sputum smear-negative PTB cases.

Aim: To determine the diagnostic role of CBNAAT in detecting drug resistance smear negative PTB.

Materials & Methods:  The retrospective study obtained the data on patient samples registered to Revised National TB Control Programme during the period January 2018 to December 2019 due to suspected PTB. Acid-Fast Bacilli (AFB) smear and CBNAAT were carried out for all the collected samples. The incidence of rifampicin resistance was also evaluated. Descriptive statistics was carried out using suitable parametric and non- parametric tests of significance. Comparison of parameters was carried out using chi-square test for counts data.

Results: A total 3652 suspected cases were screened using AFB smear and CBNAAT, and the corresponding number of positive cases reported were 291 (7.97%) and 337(9.23%) (P 0.055, Table 1, Fig. 1). The mean age of the positive patients was 41.53±15.22 years and the male-to-female ratio noted was 1:0.33. Out of 337 positive patients, 46(13.65%) were diagnosed as negative in AFB, and all these patients were diagnosed as positive (100%) in CBNAAT (Table 2, Fig. 2,P < 0.00001).Thirty-five(10.39%) TB-positive patients were found to be drug resistant (P <0.00001) and the number of subjects resistant to rifampicin, isoniazid and both were 31(9.2%),3(0.89%) and 1(0.3%) respectively (Table 3, Fig. 3). In smear negative patients (n=46), 4 were found rifampicin resistant (8.70%), whereas in smear-positive patients (n=31, 10.65%), resistance to rifampicin, isoniazid and both were noted in 27(9.28%), 3(1.03%) and 1(0.34%) subjects respectively (Fig. 4).

Conclusion: The study corroborates the potential of CBNAAT in identifying drug resistance in smear negative PTB.