QuantiFERON-TB Gold Plus and QuantiFERON-TB Gold In-tube assays for detecting latent tuberculosis infection in Thai healthcare workers

Detecting latent tuberculosis infection (LTBI) is important, especially in high-risk populations including healthcare workers (HCWs). QuantiFERON-TB Gold Plus (QFT-Plus) is a new version of the interferon-gamma release assays (IGRAs) to replace the QuantiFERON-TB Gold In-tube (QFT-GIT). However, data on the use of QFT-Plus for LTBI detection in high TB-burden countries are limited. This study was conducted in a TB-endemic setting in Thailand. HCWs were enrolled in the study and underwent both tests during the annual health screening. The testing results were compared and the concordance was determined. Of 102 HCWs, 11 (10.78%) were positive according to both tests, and 15 (14.71%) were positive according to QFT-Plus. The overall agreement between assays was 96.08%, with Cohen’s kappa coefficient (k) at 0.82. All four discordant results occurred with QFT-GIT negative and QFT-Plus positive. The comparison between QFT-GIT and QFT-Plus based on each antigen tube (TB1 or TB2) exhibited similar concordance with 99.02% and 95.10% agreement, respectively. The intra-comparison between TB1 and TB2 of QFT-Plus also showed good concordance at 96.08%. Among this group of HCWs, the LTBI prevalence of any positive results in both tests was low. Overall, the study showed good agreement between QFT-Plus and QFT-GIT (k = 0.82) with a minimal difference, suggesting similar assay performance to that mainly carried out in TB-low incidence countries. The results support the use of QFT-Plus for detecting LTBI in a format similar to QFT-GIT

QuantiFERON-TB Gold In-Tube test in active tuberculosis patients and healthy adults

Interferon-gamma (IFN-γ) release assays have improved latent tuberculosis (TB) detection and have been considered promising for the diagnosis of TB disease. However, diagnosis efficacy data is limited in high burden countries. The aim of this study was to determine the diagnostic potential of the QuantiFERON-TB Gold In-Tube (QFT-GIT) test for the diagnosis of active TB in an endemic setting for TB. A cross-sectional study was conducted in a group of 102 Thai patients with clinical symptoms and chest x-ray findings suggesting of active pulmonary TB and a group of 112 healthy adults. Testing was carried out using sputum microscopy, mycobacterial culture and QFT-GIT test. Of these patients, QFT-GIT was positive in 73 (71.57%), negative in 27 (26.47%), and undetermined in 2 (1.96%) cases. Among healthy controls, QFT-GIT was positive in 18 (16.07%), negative in 93 (83.04%), and undetermined in 1 (0.89%) person. Based on TB culture results, the sensitivity of QFTGIT for diagnosing active TB was 84.21% (95% confidence interval (CI); 72.13-92.52). The positive and negative predictive values were 65.75% (95% CI; 59.26-71.70) and 66.67% (95% CI; 49.94-80.04), respectively. The median IFN-γ level in culture-confirmed TB patients was 3.91 compared to 0.03 IU/mL of the healthy group. QFT-GIT appears to be a useful indirect test for TB diagnosis in Thailand and its use is recommended in association with clinical and radiological assessments for identifying active or latent TB

The performance of an in-house loop-mediated isothermal amplification for the rapid detection of Mycobacterium tuberculosis in sputum samples in comparison with Xpert MTB/RIF, microscopy and culture

Simple, low-cost and effective diagnostic tests for tuberculosis (TB) are needed especially in TB-high burden settings. The present study evaluated the performance of an in-house loop-mediated isothermal amplification (LAMP) for diagnosing TB by comparing it to Xpert MTB/RIF, microscopy and culture. In Thailand, a total of 204 excess sputum samples volume after the processing of cultures were used for Mycobacterium tuberculosis (MTB) detection by Xpert MTB/RIF and LAMP. Based on culture results as the gold standard, the overall sensitivity of LAMP and Xpert MTB/RIF were 82.1% (126/153; 95% confidential interval [CI]: 75.4-88.98%) and 86.9 % (133/153; 95% CI: 80.5-90.8%) respectively, and the specificity of both tests was 100% (51/51; 95% CI: 93.0-100.0%). In comparison with Xpert MTB/RIF, the sensitivity and specificity of LAMP were 94.7% (126/133; 95% CI: 89.5-97.9%), and 100.0% (73/73; 95% CI: 94.9-100.0%), respectively. The average threshold cycle (Ct) of Xpert MTB/RIF detection for positive and negative LAMP results was statistically different, of 18.4 and 27.0, respectively (p < 0.05). In comparison with the acid-fast staining technique, and analyzing LAMP and Xpert MTB/RIF in smear-negative/ culture-positive specimens, there was an increase of the detection rate by 47.7% (21/44) and 54.6% (24/44). The diagnostic sensitivity and specificity of LAMP appeared to be comparable to those of Xpert MTB/RIF. We claim that this LAMP has potential to provide a sensitive diagnostic test for the rapid TB diagnosis. It allowed a fast detection of MTB before the cultures and it could be used in resource-limited laboratory settings

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

Drug-resistant Mycobacterium tuberculosis and its genotypes isolated from an outbreak in western Thailand

Background: Multidrug-resistant TB (MDR-TB) outbreaks have occurred in the Thamaka district, Kanchanaburi province in Thailand. Methods: Seventy-two isolates, which included 7% mono-, 30.6% MDR and extensively drug-resistant TB (XDR-TB), were genotyped by spoligotyping, mycobacterial interspersed repetitive unit-variable-number tandem repeat (MIRU-VNTR) and single nucleotide polymorphism genotyping, and their drug resistance was analysed. Results: The spoligotyping results showed that Beijing spoligo-international type (SIT)1 was predominant (n=38; 52.8%) while the remaining were non-Beijing sublineages (n=34). The MIRU-VNTR analysis showed that Beijing isolates, most of which belonged to the modern type (n=37), formed 5 clusters and 13 individual patterns. In katG, only mutation Ser315Thr was identified. In rpoB, Ser531Leu was predominant, except for His526Arg and Leu533Pro, which were found in two isolates. A cluster of 14 Beijing strains contained these common mutations and shared the MIRU-VNTR genotype with isolates in the Thamaka district that had spread previously. Two U SIT523 isolates contained the mutations A1400G in rrs and Asp94Gly in gyrA genes, indicating a spread of XDR-TB. Conclusions: Most mutations were associated with drug resistance and the specific MDR Beijing and XDR-TB in U SIT523 isolates remain. This genotyping is a key tool for tracking TB transmission in the Thamaka district of Thailand

Putative extensive and pre-extensive drug resistant-tuberculosis associated with unusual genotypes on the Thailand-Myanmar border

Extensive drug-resistant tuberculosis (XDR-TB) is highly life threatening and its diagnosis is usually difficult and time-consuming. Here we present the first two cases of XDR and pre-XDR-TB diagnosed in 2018 on the Thailand-Myanmar border, more specifically in Tak province. Rapid detection of XDR-TB was performed by loop-mediated isothermal amplification (LAMP), Xpert MTB/RIF, and line probe assays. Mutation analyses targeting rpoB, katG, inhA, gyrA and rrs genes showed an association with drug-resistant phenotypes, except for rifampicin resistance. Spoligotyping revealed uncommon Beijing and T2 genotypes and the analysis of M. tuberculosis interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) showed the presence of more polymorphisms. This report highlights the importance of the early detection of drug-resistant tuberculosis by molecular tests followed by phenotyping assays. Based on the up-to-date definition of XDR- and pre-XDR-TB, the susceptibility testing for bedaquiline and linezolid is required and the two reported cases may correspond to putative XDR-TB