Comparison of Loop-Mediated Isothermal Amplification, Microscopy, Culture, and PCR for Diagnosis of Pulmonary Tuberculosis

Efficacy of LAMP assay for Mycobacterial spp. detection to prevent treatment delays and onset of drug resistance: a systematic review and meta-analysis

Background

Tuberculosis (TB) remains a deadly disease affecting one-third population globally. Long turnaround time and poor sensitivity of the conventional diagnostics are the major impediments for faster diagnosis of Mycobacterial spp to prevent drug resistance. To overcome these issues, molecular diagnostics have been developed. They offer enhanced sensitivity but require sophisticated infrastructure, skilled manpower and remain expensive.

Methods

In that context, loop-mediated isothermal amplification (LAMP) assay, recommended by the WHO in 2016 for TB diagnosis, sounds as a promising alternative that facilitates visual read outs. Therefore, the aim of the present study is to conduct a meta-analysis to assess the diagnostic efficiency of LAMP for the detection of a panel of Mycobacterium spp. following PRISMA guidelines using scientific databases. From 1600 studies reported on the diagnosis of Mycobacterium spp., a selection of 30 articles were identified as eligible to meet the criteria of LAMP based diagnosis.

Results

It was found that most of the studies were conducted in high disease burden nations such as India, Thailand, and Japan with sputum as the most common specimen to be used for LAMP assay. Furthermore, IS6110 gene and fluorescence-based detections ranked as the most used target and method respectively. The accuracy and precision rates mostly varied between 79.2% to 99.3% and 73.9% to 100%, respectively. Lastly, a quality assessment based on QUADAS-2 of bias and applicability was conducted.

Conclusion

LAMP technology could be considered as a feasible alternative to current diagnostics considering high burden for rapid testing in low resource regions.

Diagnostic accuracy of nanopore sequencing using respiratory specimens in the diagnosis of pulmonary tuberculosis

OBJECTIVES

The aim of this study was to assess the role of nanopore sequencing using respiratory specimens in the early diagnosis of pulmonary tuberculosis (PTB) and simultaneously compare it head-to-head with Mycobacterium tuberculosis (MTB) culture, and Xpert MTB/rifampin (RIF).

METHODS

The clinical data of 164 patients with suspected PTB were retrospectively reviewed to determine the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the curve (AUC) of the acid-fast bacilli (AFB) smear, MTB culture, Xpert MTB/RIF, and nanopore sequencing and assess their diagnostic accuracy compared with culture combined with clinical diagnosis.

RESULTS

The overall sensitivity, specificity, PPV, NPV, and AUC of the AFB smear were 27.6%, 87.5%, 84.2%, 33.3%, and 0.58, respectively; for MTB culture, these values were 57.8%, 100.0%, 100.0%, 49.5%, and 0.79, respectively; for Xpert MTB/RIF, these values were 62.9%, 97.9%, 98.7%, 52.2%, and 0.80, respectively; and for nanopore sequencing, these values were 94.8%, 97.9%, 99.1%, 88.7%, and 0.96, respectively.

CONCLUSION

The diagnostic accuracy of nanopore sequencing was excellent in terms of PTB diagnosis and was considerably better than that of the Xpert MTB/RIF and MTB culture. Nanopore sequencing could be an effective alternative to Xpert MTB/RIF for the initial detection of PTB to improve the accuracy of PTB diagnosis.

Loop mediated isothermal amplification of Clostridioides difficile isolates in gastrointestinal patients

This study investigated the prevalence of Clostridioides difficile by culture, multiplex polymerase chain reaction (M-PCR), and loop mediated isothermal amplification (LAMP) in patients with suspected C. difficile infections (CDIs). Also, the results of three methods were compared. All stool specimens collected from CDI suspected patients were cultured on selective C. difficile cycloserine-cefoxitin fructose agar and incubated in an anaerobic jar up to 7 days. The bacterial isolates were identified using standard tests. Multiplex-PCR (M-PCR) was performed for detection of tcdA, tcdB, and tpi genes. The LAMP assay was performed to detect the tcdB gene of C. difficile. C. difficile was isolated from 20.0% (n = 10/50) of samples by culture. M-PCR showed that 34.0% (n = 17/50) of the specimens were positive for C. difficile based on the presence of tpi gene. Out of the 17 C. difficile, 13 strains (76.0%) were positive for tcdB gene using M-PCR. However, the LAMP assay showed that 30.0% (15/50) of specimens were positive for the presence of tcdB gene. M-PCR and LAMP methods showed 100.0% sensitivity compared to the culture method. However, the specificity of the LAMP (87.5%) was relatively higher than the M-PCR (82.5%) compared to the culture. Based on the results of this study, the prevalence of toxigenic C. difficile strains was high in suspected CDI patients. So, the differentiation between toxigenic and non-toxigenic strains is necessary. Our data showed that the LAMP assay is a good method for direct detection of toxigenic C. difficile strains from stool specimens.

Evaluation of an in-house loop-mediated isothermal amplification for Mycobacterium tuberculosis detection in a remote reference laboratory, Thailand

Loop-mediated isothermal amplification (LAMP) is a simple and efficient nucleic acid amplification method for the rapid diagnosis of infectious diseases. This study assessed the performance of an in-house LAMP for tuberculosis (TB) diagnosis at a remote reference laboratory in the endemic setting of Thailand. As part of the routine service, 1,882 sputum samples were processed for mycobacterial culture in Lowenstein-Jensen and MGIT media. The DNA was extracted from the remaining decontaminated samples after the culture procedure for real-time polymerase chain reaction (PCR) analysis using Anyplex plus MTB/NTM detection kit. 785 (40.28%) were positive by mycobacterial culture. Of these, 222 DNA remnants were available and subjected to LAMP analysis. Based on culture as reference (Mycobacterium tuberculosis; MTB= 209/ non-tuberculous mycobacteria; NTM= 13), the overall sensitivity of LAMP and Anyplex plus assays for MTB detection were 89.95% (188/209; 95% confidential interval [CI]: 85.05-93.67%) and 96.65% (202/209; 95% CI: 93.22-98.64%), and the accuracy values were 88.74% (197/222; 95% CI: 83.83-92.58) and 96.40% (214/222; 93.02-98.43%), respectively. The sensitivity and accuracy of the in-house LAMP and the Anyplex plus real-time PCR assay were high in comparison to culture results. The high sensitivity and accuracy suggested that this in-house LAMP was promising and might be useful for early TB diagnosis.

Pragmatic accuracy of an in-house loop-mediated isothermal amplification (LAMP) for diagnosis of pulmonary tuberculosis in a Thai community hospital

BACKGROUND

To improve the quality of diagnosing pulmonary tuberculosis (TB), WHO recommends the use of rapid molecular testing as an alternative to conventional microscopic methods. Loop-mediated isothermal amplification assay (LAMP test) is a practical and cost-effective nucleic amplification technique. We evaluated the pragmatic accuracy of an in-house LAMP assay for the diagnosis of TB in a remote health care setting where an advanced rapid molecular test is not available.

METHODS

A prospective diagnostic accuracy study was conducted. Patients with clinical symptoms suggestive of TB were consecutively enrolled from April to August 2016. Sputum samples were collected from each patient and were sent for microscopic examination (both acid-fast stain and fluorescence stain), in-house LAMP test, and TB culture.

RESULTS

One hundred and seven patients with TB symptoms were used in the final analysis. This included 50 (46.7%) culture-positive TB patients and 57 (53.3%) culture-negative patients. The overall sensitivity of the in-house LAMP based on culture positivity was 88.8% (95/107) with a 95%CI of 81.2-94.1. The sensitivity was 90.9% (40/44) with a 95%CI of 78.3-97.5 for smear-positive, culture-positive patients, and was 16.7% (1/6) with a 95%CI of 0.4-64.1 for smear-negative, culture-positive patients. The overall sensitivity of the in-house LAMP test compared to smear microscopy methods were not significantly different (p = 0.375). The specificity of the in-house LAMP based on non-TB patients (smear-negative, culture-negative) was 94.7% (54/57) with a 95%CI of 85.4-98.9.

CONCLUSIONS

The diagnostic accuracy of the in-house LAMP test in a community hospital was comparable to other previous reports in terms of specificity. The sensitivity of the in-house assay could be improved with better sputum processing and DNA extraction method.