Comparison of the Efficacies of Loop-Mediated Isothermal Amplification, Fluorescence Smear Microscopy and Culture for the Diagnosis of Tuberculosis

Geojith George,John Kenneth,Prem Mony,Shuang-Yong Xu

doi:10.1371/journal.pone.0021007

Abstract

BackgroundDespite the advent of novel diagnostic techniques, smear microscopy remains as the most practical test available in resource-limited settings for tuberculosis (TB) diagnosis. Due to the low sensitivity of microscopy and the long time required for culture, feasible and accessible rapid diagnostic methods are urgently needed. Loop-mediated Isothermal Amplification (LAMP) is a promising nucleic-acid amplification assay, which could be accessible, cost-effective and more suited for use with unpurified samples.Methodology/Principal FindingsIn the current study, the objective was to assess the efficacy of a LAMP assay for tuberculosis compared with fluorescence smear microscopy as well as Löwenstein-Jensen (LJ) and Mycobacteria Growth Indicator Tube (MGIT) cultures for the diagnosis of pulmonary tuberculosis using sputum samples. Smear microscopy and culture were performed for decontaminated and concentrated sputum from TB suspects and the LAMP was also performed on these specimens. The LAMP and smear microscopy were compared, in series and in parallel, to culture. LAMP and smear microscopy showed sensitivities of 79.5% and 82.1% respectively and specificities of 93.8% and 96.9% respectively, compared to culture. LAMP and smear in series had sensitivity and specificity of 79.5% and 100.0% respectively. LAMP and smear in parallel had sensitivity and specificity of 82.1% and 90.6% respectively.Conclusions/SignificanceThe overall efficacies of LAMP and fluorescence smear microscopy in the current study were high and broadly similar. LAMP and smear in series had high specificity (100.0%) and can be used as a rule-in test combination. However, the performance of LAMP in smear negative samples was found to be insufficient.

Highlights

Tuberculosis (TB) is one of the oldest diseases that still afflict mankind
Loop-mediated Isothermal Amplification (LAMP) and smear in series had high specificity (100.0%) and can be used as a rule-in test combination
LAMP and smear microscopy were compared in series (LAMP performed only if smear positive and considered TB positive if both tests are positive or TB negative if either test is negative) and in parallel (LAMP performed for all samples and considered TB positive if either smear or LAMP is positive and TB negative if both are negative)

Summary

Introduction

Tuberculosis (TB) is one of the oldest diseases that still afflict mankind. The dual specters of TB and AIDS have drawn recent attention to the lack of a suitable diagnostics for TB [1,2,3,4]. The culture which is considered as the ‘gold standard’ of TB diagnosis takes 3–6 weeks, leaving the less sensitive smear microscopy as the only feasible rapid test presently. A highly sensitive rule-in test can significantly improve the case detection whereas a highly specific rule-out test can reduce the turnaround time and the duration of respiratory isolation as well as avoid unnecessary administration of potentially toxic drugs [9,10,11]. Despite the advent of novel diagnostic techniques, smear microscopy remains as the most practical test available in resource-limited settings for tuberculosis (TB) diagnosis. Due to the low sensitivity of microscopy and the long time required for culture, feasible and accessible rapid diagnostic methods are urgently needed. Loop-mediated Isothermal Amplification (LAMP) is a promising nucleic-acid amplification assay, which could be accessible, cost-effective and more suited for use with unpurified samples

Methods

Results

Conclusion