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2017 Month : September Volume : 6 Issue : 74 Page : 5281-5286

EVALUATION OF CARTRIDGE BASED NUCLEIC ACID AMPLIFICATION TEST IN DIAGNOSIS OF PULMONARY TUBERCULOSIS.

Subhasis Mukherjee1, Debabani Biswas2, Shabana Begum3, Priyanka Ghosh4, Amitava Paul5, Supriya Sarkar6

Corresponding Author:
Dr. Debabani Biswas,
#607, Purbalok, Kalikapur,
Plot No. 328, Kolkata-700099, West Bengal.
E-mail: debabanibiswas@gmail.com

ABSTRACT

BACKGROUND

Tuberculosis still continues to be one of the commonest cause of infectious disease related morbidity in the developing world. Diagnosis of pulmonary tuberculosis is mostly relied on sputum smear microscopy and sputum for mycobacterial culture. In recent years, cartridge based nucleic acid amplification test (CBNAAT) has been recommended by World Health Organization as a rapid diagnostic test for detection of tuberculosis and rifampicin resistance.

The aim of this study is to determine the diagnostic yield of CBNAAT in pulmonary tuberculosis (PTB) and to compare its efficacy between sputum smear-positive and sputum smear-negative pulmonary tuberculosis.

MATERIALS AND METHODS

A prospective observational study was conducted in the Department of Respiratory Medicine in a teaching hospital in eastern India for a period of one year. All re-treatment cases of PTB, newly detected smear-negative PTB and all human immunodeficiency virus-PTB co-infected cases were recruited for the study and sputum for CBNAAT was performed in all of them. Results were analysed in light of diagnostic yield of CBNAAT with special emphasis on comparing CBNAAT results between different subgroups- sputum smear-positive, sputum smear-negative PTB and immunocompromised patients.

 

RESULTS

Out of 228 cases of PTB, 190 were sputum smear negative and 38 cases were sputum smear positive. Mean age of the study population was 33 ± 17.13 years. Sensitivity of sputum smear for AFB was 16.67% (CI-12.07%-22.15%) with a negative predictive value (NPV) of 20.83% (CI- 19.89%-21.81%). Sputum smear negativity was found to be more common in females. CBNAAT was positive in 111 cases. Overall, sensitivity of CBNAAT was 48.68% (95% CI- 42.03%-55.37%). Sensitivity of CBNAAT varied significantly between sputum smear-positive PTB (100%, CI- 92.89%-100%) and sputum smear-negative PTB (38.42%; CI- 31.47%-45.74%) (p- <0.0001). Sensitivity of CBNAAT was 33.33% (CI-17.96%-51.83%) in PTB-HIV co-infected patients. Rifampicin resistance was detected in five (2.2%) patients with 100% sensitivity and specificity.

CONCLUSION

CBNAAT adds significantly to the diagnostic yield of PTB in comparison to sputum smear microscopy, but its sensitivity is lower in sputum smear-negative cases. It has additional advantage of identifying rifampicin resistance with high sensitivity and specificity.

KEYWORDS

Pulmonary Tuberculosis, Nucleic Acid Amplification Test, Smear Positive, Smear Negative, Human Immunodeficiency Virus.

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