Evaluation of Loopamp Assay for the Diagnosis of Pulmonary Tuberculosis in Cambodia.

Sokleaph Cheng,Tan Eang Mao,Anne-Laure Bañuls,Alexandra Kerléguer,Sok Heng Pheng,Guy B Marks,Seiha Heng

doi:10.1155/2020/6828043

Abstract

The Loopamp™ MTBC kit (TB-LAMP) is recommended by WHO for Mycobacterium tuberculosis complex detection in low-income countries with a still low drug-resistant tuberculosis (TB) rate. This study is aimed at testing its feasibility in Cambodia on sputa collected from presumptive tuberculosis patients. 499 samples were tested at a smear microscopy center and 200 at a central-level mycobacteriology laboratory. Using mycobacterial cultures as reference, TB-LAMP results were compared with those of LED fluorescent microscopy (LED-FM) and Xpert® MTB/RIF. At the microscopy center, TB-LAMP sensitivity was higher than that of LED-FM (81.5% [95% CI, 74.5-87.6] versus 69.4% [95% CI, 62.2-76.6]), but lower than that of the Xpert assay (95.5% [95% CI 92.3-98.8]). At the central-level laboratory, TB-LAMP sensitivity (92.8% [95% CI, 87.6-97.9]) was comparable to that of Xpert (90.7% [95% CI, 85.0-96.5]) using stored sample. No significant difference in terms of specificity between TB-LAMP and Xpert assays was observed in both study sites. In conclusion, our data demonstrate that TB-LAMP could be implemented at microscopy centers in Cambodia to detect TB patients. In addition, TB-LAMP can be a better choice to replace smear microscopy for rapid TB diagnosis of new presumptive TB patients, in settings with relative low prevalence of drug-resistant TB and difficulties to implement Xpert assay.

Highlights

Despite the availability of highly efficacious treatments for decades, tuberculosis remains a major public health issue worldwide
Our findings indicate that the sensitivity of the LoopampTM assay for TB diagnosis (TB-Loopmediated isothermal amplification (LAMP)) is superior to that of sputum smear microscopy using the LED-fluorescent method, but inferior to that of the Xpert® MTB/RIF (Xpert) MTB/RIF test at the smear microscopy center
No significant difference in sensitivity and specificity was found for TB-LAMP compared to Xpert in central-level laboratory evaluation

Summary

Introduction

Despite the availability of highly efficacious treatments for decades, tuberculosis remains a major public health issue worldwide. The most widely used method for TB diagnosis is sputum smear microscopy. This test is simple, rapid, and inexpensive but has a relatively low sensitivity, in patients with extrapulmonary TB, children, and in people with HIV [2]. Among the technologies developed and implemented over the past decade, nucleic acid amplification technologies hold the greatest promise of substantial gains in turnaround-time (compared with culture) and in sensitivity and specificity (compared with smear microscopy) [2,3,4]. Loopmediated isothermal amplification (LAMP) has several advantages: no need of sophisticated instrumentation, DNA amplification of partially processed or unprocessed samples, and visual readout of the amplified products [5]. In 2016, WHO recommended using the LoopampTM MTBC assay (TB-LAMP) for the detection of Mycobacterium

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Conclusion