Validity of a CB-NAAT assay in diagnosing tuberculosis in comparison to culture: A study from an urban area of South India

*, Aishwarya Raj and Baliga, Shrikala and Shenoy, Suchitra Mala and *, Dhanashree B and *, Prasanna Mithra P and Nambiar, Smitha K and *, Leesha Sharon (2020) Validity of a CB-NAAT assay in diagnosing tuberculosis in comparison to culture: A study from an urban area of South India. Journal of Clinical Tuberculosis and Other Mycobacterial Diseases, 21 (12). pp. 1-4. ISSN 24055794

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Abstract

1. Introduction The world today is known for its advancements in technology in all social sectors, most importantly in the health sector and specifically in the field of Mycobacteriology. Clinically suspected TB cases are normally tested for the presence of Mycobacterium tuberculosis in appropriate samples by laboratory diagnostic methods. Conventionally, Acid fast bacilli (AFB) smear microscopy and the culture methods are employed for the diagnosis. Fluorescence microscopy of Auramine-O stained smears and liquid culture using tools like the BACTEC™ “Mycobacterial Growth Indicator Tube 960” (MGIT 960; BectonDickinson, Sparks, MD, USA) are the most commonly used conventional methods. Culture method is the most sensitive and specific method for the detection of Mycobacterium tuberculosis. Despite this, cultures are highly prone to contamination and the process can still take several days and does require expensive equipment, strict biosafety practices and well trained technical staff [1]. Among the currently available Nucleic Acid Amplification Tests (NAAT), the Xpert MTB/RIF Assay (CB-NAAT), the LINE Probe Assay (LPA) and the Loop-Mediated Isothermal Amplification (LAMP) are endorsed by WHO for in vitro diagnosis of TB. The GeneXpert® system powered by the Cepheid Innovations, for the CB-NAAT (Cartridge based), is an automated, semi-quantitative, hemi-nested, real-time PCR used for the simultaneous detection of the MTB complex and its rifampicin (RIF) resistance pattern associated with the mutation in the rpoB gene, in clinical samples with a 2 h turnaround time [2]. The present study was carried out to assess the performance of CBNAAT (Cepheid GeneXpert®) system for the diagnosis of MTB in both pulmonary and extrapulmonary specimens, within the demographic area of Mangalore, in South Karnataka. 2. Materials and methods The study was approved by the Institutional Ethics Committee of Kasturba Medical College, Mangalore. This cross-sectional study was conducted at the Department of Microbiology, Kasturba Medical College, Mangalore, Manipal Academy of Higher Education, Manipal, in Dakshina Kannada District of Karnataka State in India, over a period of 31 months from June 2016 to December 2018. The Department of Microbiology consists of Designated Microscopy Center as per the Revised National Tuberculosis Control Program (RNTCP) under the DOTS (Directly Observed Treatment, Short course), which caters to attached tertiary care hospitals of the study Institute. The health care provided in these hospitals includes people from neighboring Districts of Karnataka and Kerala States. Pulmonary & extrapulmonary specimens received at the Microbiology laboratory, in sterile containers, from the clinically suspected tuberculosis patients were used in the study. Saliva, blood, urine and stool samples were excluded from the study. The samples received at the laboratory were divided into three portions, one part each was used for AFB direct smear preparation, CBNAAT and MGIT liquid culture, respectively. Direct and concentrated smears were prepared, stained using the Fluorochrome acid-fast staining method, with the Auramine-O fluorescent stain and screened as per the guidelines [3]. A smear was reported positive if either the direct or the concentrated smear showed the presence of AFB. The NALC-NaOH method [4] was used for the sample digestion and decontamination. The concentrates were cultured on to BD BBL™ MGIT™ Mycobacteria Growth Indicator Tube using the BACTEC™ MGIT™ 320 system. Cultures were incubated for up to 8 weeks to confirm the negativity of Mycobacteria in the sample. If positive, the culture was subjected to a rapid immunological ID test using the BD MGIT™ TBc ID test device to differentiate MTB from Mycobacterium genus. CB-NAAT was done using

Item Type: Article
Uncontrolled Keywords: tuberculosis, CB NAAT,
Subjects: Medicine > KMC Mangalore > Microbiology
Medicine > KMC Mangalore > Community Medicine
Depositing User: KMCMLR User
Date Deposited: 30 Dec 2020 03:55
Last Modified: 30 Dec 2020 03:55
URI: http://eprints.manipal.edu/id/eprint/156149

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