Evaluating Truenat Assay for the Diagnosis of Ocular Tuberculosis and Detection of Drug Resistance.

Background: Truenat MTB Plus assay was evaluated for diagnosing ocular tuberculosis (OTB) and detecting multi-drug resistant (MDR) and extremely-drug resistant (XDR) OTB.

Methods: A total of 75 vitreous fluid specimens [five confirmed OTB, 40 clinically suspected OTB and 30 controls] were subjected to Truenat MTB Plus, multiplex PCR, and Xpert Ultra. Chips of Truenat were used for detecting rifampicin, isoniazid, fluoroquinolone and bedaquiline resistance. The performance was compared against culture, composite reference standard, and gene sequencing.

Results: The overall sensitivity of TruePlus, MPCR, and Ultra in diagnosing OTB was 66.6%, 73.3%, and 55.5%, respectively. Out of six cases with mutations in rpoB gene, RifR was detected in five by TrueRif and four by Ultra. Three MDR and one XDR-OTB were reported by Truenat.

Conclusion: Truenat assay along with its strategic chips is a rapid and reliable tool for diagnosis of OTB and detection of drug resistance, including MDR and XDR-OTB. OTB: Ocular tuberculosis; XDR: Extremely drug resistant; Ultra: Xpert MTB/RIF Ultra; Xpert: Xpert MTB/RIF; PCR: polymerase chain reaction; NAATs: Nucleic acid amplification tests; MDR: Multi Drug Resistant; NSP: National Strategic plan for elimination of tuberculosis; FqR: Fluoroquinolone resistant; BdqR: bedaquiline resistant; TrueRif: Truenat MTB Rif Dx; TruePlus: Truenat Plus; INH: Isoniazid; DST: Drug susceptibility testing; MGIT: Mycobacterial growth indicator tube; CRF: Composite reference standard; PPV: positive predictive value; NPV: negative predictive value; EPTB: extrapulmonary tuberculosis; VF: vitreous fluid; DNA: deoxyribonucleic acid; ATT: antitubercular therapy; RifR: Rifampicin resistance; RifS: Rifampicin susceptible; RifI: Rifampicin indeterminate.