Field evaluation of the direct colorimetric nitrate reductase assay method for the simultaneous detection of multidrug-resistant (MDR)- and extensively-drug- resistant (XDR)-tuberculosis (TB) in Argentina

IMPERIALE B; MORCILLO N; PALOMINO JC; MARTIN A

Congreso; 23 Congress of the European Society of clinical Microbiology and Infectious Diseases; 2013

European Society of clinical Microbiology and Infectious Diseases

Objectives: The spread of MDR-TB and XDR-TB stresses the need for quick and affordable diagnostic tools, particularly for low- and middle-income countries, with a high prevalence of TB. The objective of this study was to evaluate the previously described Nitrate Reductase Assay for the simultaneous detection of MDR and XDR-TB patients directly on sputum samples (D-NRA). Methods: The performance of D-NRA was compared with the BACTEC MGIT960 assay under routine conditions. Sputum smear-positive samples were decontaminated with the NALC method and inoculated in Lowenstein-Jensen tubes containing drugs and 1 mg/ml of potassium nitrate. The following drugs were tested: rifampicin (RMP), isoniazid (INH), ofloxacin (OFLO), kanamycin (KAN). Consecutive smear-positive samples (n= 92) were prospectively analysed with DNRA and compared to BACTEC MGIT960 to detect resistance to INH, RMP, KAN and OFLO. PNB was included for the simultaneous identification of Mycobacterium tuberculosis complex. Results: Out of 92 smearpositive samples, 6 failed to growth and 2 were identified as non-tuberculosis mycobacteria. For the 84 samples that grew, the NRA sensitivity, specificity, positive and negative predictive values for all drugs were 100%. The mean time to obtain results with the D-NRA was 13.9 days and the overall agreement between D-NRA and the BACTEC MGIT960 was 100% for all drugs. Conclusion: D-NRA offers timely drug resistance detection of M. tuberculosis resistance to first- and second-line drugs. D-NRA was user-friendly, easy to implement in limited laboratory facilities and provide an easy interpretation of results by a simple visual change of color