The first insight into Mycobacterium tuberculosis complex isolates in the lower northern region in Thailand

BACKGROUND

Tuberculosis (TB) remains an important infectious disease and different genotypes have been reported. This study aimed to investigate the genetic diversity and molecular epidemiology of TB in the lower northern region of Thailand, where genotyping data are limited.

METHODS

A total of 159 Mycobacterium tuberculosis complex (MTBC) isolates from this region were genotyped by spoligotyping and the major spoligotypes were further subdivided by the mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) method.

RESULTS

Spoligotyping identified 34 types and classified them into 14 clusters. East African-Indian (EAI) groups were the most frequent (44.7%), followed by Beijing (36.5%), with a higher prevalence of drug resistance. By 15-loci MIRU-VNTR typing, the major groups of the Beijing and EAI2_NTB were further differentiated into 44 and 21 subtypes forming 9 and 5 subclusters with cluster rates of 0.26 and 0.44, respectively. The Hunter-Gaston Discriminatory Index among the Beijing and EAI2_NTB groups were 0.987 and 0.931, respectively, indicating high diversity.

CONCLUSIONS

This is the first look at the MTBC genotypes in the lower northern region of Thailand, which could aid in understanding the distribution and potential spread of MTBC and Mycobacterium bovis in the target region to support TB control in Thailand.

Clinical Performance of the Reverse Transcription-Loop-Mediated Isothermal Amplification Assay for the Diagnosis of COVID-19 in a Thai Community Hospital at the Thailand-Myanmar Border

INTRODUCTION

Coronavirus disease 2019 (COVID-19) continues to be a global health threat and is a public health issue in Thailand and other countries. The extensive cross-border between Thailand and Myanmar is considered to be at a potentially high risk for COVID-19 distribution in this region. In this instance, simple and cost-effective tests for rapid and early detection of COVID-19 would be useful for effective patient management and control of the disease.

METHODS

This study was conducted at Mae Sot Hospital on the border of Thailand-Myanmar to evaluate the diagnostic performance of a simple colorimetric reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay developed recently for the rapid detection of SARS-CoV-2. Nasopharyngeal specimens were routinely collected and processed through automated nucleic acid extraction followed by real-time reverse transcription-polymerase chain reaction (rRT-PCR) using the Molaccu® COVID-19 Detection Kit. The RT-LAMP assay was further performed on remnant RNA samples, and the visual results were compared to those of rRT-PCR as a reference.

RESULTS

Of the 727 samples tested, the RT-LAMP assay could detect 322 out of 374 samples positive for SARS-CoV-2 by rRT-PCR with 100% (n = 353/353) negative agreement. The comparative analysis demonstrated the overall accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of the RT-LAMP at 92.85% (n = 675/727, 95% CI: 90.73-94.61), 86.10% (n = 322/374, 95% CI: 82.17-89.44), 100% (n = 353/353, 95% CI: 98.96-100), 100% (n = 322/322, 95% CI: 98.86-100), and 87.16% (n = 353/405, 95% CI: 84.06-89.73), respectively.

CONCLUSION

This RT-LAMP assay showed good diagnostic performance in the hospital setting. It can increase laboratory capacity for rapid SARS-CoV-2 testing and has the potential for use as an alternative or a backup assay at the point of need, especially where alternatives are unavailable for any reason, such as a decline in COVID-19 cases.

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.

Molecular Characterization of Mutations in Isoniazid- and Rifampicin-Resistant Mycobacterium tuberculosis Isolated in Thailand

The control of drug-resistant tuberculosis (TB) is a major challenge. The frequency and mutation characteristics indicate the efficiency of molecular tests for the rapid detection of TB drug resistance. This study examined the existence of katG and inhA mutations for isoniazid (INH) resistance and rpoB mutations for rifampicin (RFP) resistance. In total, 178 drug-resistant Mycobacterium tuberculosis (MTB) isolates were analyzed. Mutations in katG encoding and inhA regulatory regions were detected in 136/168 (81.0%) and 29/168 (17.3%), respectively, with the most prominent mutation of Ser315Thr substitution in katG in 126/168 (75.0%), and -15 C to T substitution in the regulatory region of the inhA (26/168; 15.5%). Two distinct katG mutations (Tyr337Cys, 1003InsG) were identified. Of 125 RFP-resistant isolates, 118 (94.4%) carried mutations affecting the 81-bp RFP resistance-determining region, with the most commonly affected codons 450, 445, and 435 identified in 74 (59.2%), 26 (20.8%), and 12 (9.6%) isolates, respectively. Genetic mutations were highly associated with phenotypic INH and RFP resistance, and the majority shared similarities with those reported in previous studies in Thailand and other Asian countries. These data are useful for guiding the use and improvement of molecular tests for TB drug resistance.

Detection and factors associated with tuberculosis and rifampicin resistance among presumptive patients at the Thailand-Myanmar border

Tuberculosis (TB) continues to be a major public health problem in Thailand and many countries. Endemic TB and outbreaks of TB drug resistance in the borderlands are particularly important. The Thailand-Myanmar border has extensive cross-border travel that may accelerate TB's spread. This cross-sectional study aimed to determine the frequency and factors associated with TB, and rifampicinresistant TB (RR-TB) among presumptive tuberculosis patients in Mae Sot Hospital. Sputum was processed by microscopic examination and Xpert MTB/RIF assay. Laboratory results and socio-demographic characteristics were collected and analyzed. Univariate and multivariate analyses were performed to assess the association of the risk factors with TB and RR-TB. The significant variables at p-values < 0.05 in univariate analysis were selected for multivariate analysis. Of 365 presumptive patients enrolled, 244 (66.85%) were males and 199 (54.52%) were Burmese. Of these, 314 (86.03%) were registered as new cases and 183 (50.14%) worked as laborers. Sputum microscopy was positive in 132 (36.16%) cases. Based on Xpert MTB/RIF, the frequency of TB was 136 (37.26%) and RR-TB was 15 (11.03%). TB was more common in males than females. The majority of the cases belonged to the 26-50-year-old age group and migrant workers. In RR-TB detection, the rpoB mutations covered by probe E were the most frequently observed. Sequencing showed that the most highly mutated codon was codon 531 and Ser531Thr was the most common mutation. For risk factor analysis, working as laborers was significantly (p-value < 0.05) associated with TB (aOR 2.83; 95% CI 1.43-5.63) and previously treated cases were significantly associated with RR-TB (aOR 12.33; 95% CI 2.29-66.49). The high frequency of TB and RR-TB in migrants highlights the problem and factors associated with TB at the border and the need for efforts in TB control programs in this setting.

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.

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.

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.

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.

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

The diagnosis of tuberculosis (TB) in endemic countries is challenging due to high caseloads and limited resources. A simple and cost-effective diagnostic test for the rapid detection of Mycobacterium tuberculosis (M. tuberculosis) in clinical specimens is crucially needed. We evaluated the performance of an in-house assay based on loop-mediated isothermal amplification (LAMP) targeting the M. tuberculosis 16S ribosomal RNA (rRNA) gene for the diagnosis of TB in Thailand. A total of 252 sputum samples from suspected cases of pulmonary TB were analyzed. The sensitivity of LAMP was 99.04% (103/104; 95% confidence interval [CI]: 94.76-9.98%) and 72.73% (16/22; 95% CI: 49.78-89.27%) for smear-positive and smear-negative samples with TB-culture positivity, respectively. LAMP detected 20.69% (24/116) of TB culture negative samples but all those were positive by conventional polymerase chain reaction (PCR). The sensitivity of LAMP was higher than that of sputum microscopy while the performance of LAMP was similar to PCR. None of the samples positive for non-tuberculous mycobacteria by culture and PCR were positive by LAMP. Compared to TB culture, the positive predictive value (PPV), negative predictive value (NPV), and kappa coefficient of LAMP were 83.22%, 88.33%, and 0.75 respectively. Based on the diagnostic performance, we propose that LAMP would be suitable as a potential diagnostic test for rapid TB diagnosis in resource-limited laboratory settings.

T-SPOT®.TB test and clinical risk scoring for diagnosis of latent tuberculosis infection among Thai healthcare workers

BACKGROUND

Screening for latent tuberculosis infection (LTBI) is important to identify healthcare workers (HCWs) benefiting from preventive therapy. Interferon-gamma release assays (IGRAs) are sensitive and specific tests for LTBI diagnosis. However, in settings where IGRAs are not available, clinical risk assessment may be used as an alternative to diagnose LTBI.

METHODS

A cross-sectional study was conducted among HCWs of a tertiary-care university hospital in Thailand. All HCWs underwent T-SPOT®.TB test (T-SPOT) and assessment of LTBI clinical risks. Clinical risks associated with T-SPOT positivity were determined by multivariable logistic regression analysis and were given scores accordingly. The performance of the clinical risk scoring was evaluated in comparison to T-SPOT.

RESULTS

Among 140 enrolled HCWs, 125 (89%) were females, the median age was 27 years and 23 (16%) had T-SPOT positivity. Independent factors associated with T-SPOT positivity were age ≥30 years (adjusted odds ratio [aOR] 3.95; P = 0.002), working duration ≥60 months (aOR 3.75, P = 0.004) and frequency of TB contact ≥6 times (aOR 8.83, P = 0.005). The study's clinical risk scoring had the area under the curve by receiver operating curve analysis of 0.76 (P < 0.001) using T-SPOT positivity as a reference standard. The score of ≥3 had the best performance in diagnosing LTBI with sensitivity, specificity, positive predictive value and negative predictive value of 70%, 71%, 32% and 92%, respectively.

CONCLUSIONS

In this setting where LTBI was prevalent among HCWs but IGRAs are not widely available, the clinical risk scoring may be used as an alternative to diagnose LTBI in HCWs.

2005. T-SPOT®.TB Test for Latent Tuberculosis Infection Diagnosis and Treatment Guidance in Thai Healthcare Professionals

Background

Data on efficacy of T-SPOT^®.TB Test (T-SPOT) in diagnosing latent tuberculosis infection (LTBI) and guiding isoniazid preventive therapy (IPT) among healthcare professionals (HCP) in tuberculosis (TB)-endemic settings are limited.

Methods

A prospective study was conducted among Thai HCP undergoing T-SPOT in June 2016 (initial screening) and June 2017 (follow-up). Nine-month isoniazid preventive therapy (IPT) was offered among the HCP with positive T-SPOT. The incidence of TB and the rates of conversion and reversion of T-SPOT were evaluated during the 1-year follow-up period (June 2016 to June 2017).

Results

A total of 140 HCP underwent initial T-SPOT; the median age was 27 years (IQR 25–31 years), 89% were female and 23 (16%) were T-SPOT-positive. Eighty-nine HCP (64%) had both initial and follow-up T-SPOTs. Among the 89 HCP, the initial and follow-up rates of T-SPOT positivity were 19% (N = 17) and 24% (N = 21), respectively. The conversion and reversion rates were 10% (N = 9) and 6% (N = 5), respectively. All of the nine HCP (100%) with T-SPOT conversion reported significant contacts with patients who had active pulmonary TB without using appropriate personal protection equipment. During the 1-year follow-up period, incidence of TB were significantly higher among HCP with T-SPOT conversion compared with HCP with persistent positive T-SPOT, HCP with T-SPOT reversion and HCP with persistent negative T-SPOT [22 vs. 8 vs. 0 vs. 0 cases/100 person-years; P < 0.001]. Of the 17 HCP with positive initial T-SPOT, 8 (47%) completed IPT. The incidence of TB was significantly lower and the T-SPOT reversion rate was significantly higher among HCP completing IPT compared with HCP declining or not completing IPT (0 vs. 11 cases/100 person-years; P < 0.001 and 63% vs. 0%; P = 0.009, respectively).

Conclusion

T-SPOT could be used for diagnosing LTBI, guiding IPT and identifying HCP with subsequent risk for TB. The serial T-SPOT may be used for evaluating IPT efficacy.

Disclosures

All authors: No reported disclosures.

Loop-Mediated Isothermal Amplification for Rapid Identification of Mycobacterium tuberculosis in Comparison with Immunochromatographic SD Bioline MPT64 Rapid® in a High Burden Setting

Loop-mediated isothermal amplification (LAMP) was assessed for rapid identification of Mycobacterium tuberculosis complex (MTC) in comparison with an immunochromatographic test (ICT) using SD Bioline Ag MPT64 Rapid^®. One hundred and fifty-one MGIT cultures positive for acid-fast bacilli were tested for MTC. DNA was extracted from a small portion of culture samples by heat lysis and subjected to LAMP analysis. Of these, 144 were positive and 5 were negative by both tests. One culture that was ICT negative but was LAMP positive was confirmed to have a mutation in the mpt64 gene. The agreement was 98.68% (95% confidence interval [CI]: 94.80-99.77), and the kappa value was 0.83% (95% CI: 0.59-1.00). Good correlation results suggested that LAMP assay is a reliable molecular test for rapid identification of MTC and is practical for use in resource-limited, high burden settings.

Tuberculin Skin Test and QuantiFERON(®)-TB Gold In-Tube Test for Diagnosing Latent Tuberculosis Infection among Thai Healthcare Workers

A cross-sectional study was conducted on the performance of the tuberculin skin test (TST) and QuantiFERON(®)-TB Gold In-Tube test (QFT-IT) for detecting latent tuberculosis infection among Thai healthcare workers (HCWs). Each HCW underwent both the TST and QFT-IT during the annual health screening. Among the 260 HCWs enrolled, the median age was 30 years (range 19-60 years), 92% were women, 64% were nurses and nurse assistants, 78% were Bacillus Calmette Guérin vaccinated, and 37% had previously taken the TST. Correlation between TST reaction size and the interferon-γ level was weak (r = 0.29; P < 0.001). Of the HCWs, 38% and 20% had a reactive TST and a positive QFT-IT, respectively. Using QFT-IT positivity as a standard for latent tuberculosis diagnosis, the cut-off for TST reactivity with the best performance was ≥13 mm with a sensitivity, specificity, false positivity, and false negativity of 71%, 70%, 30%, and 29%, respectively (area under the curve 0.73; P < 0.001). The independent factor associated with a false reactive TST was a previous TST (adjusted odds ratio 1.83; P = 0.04). Our findings suggest that the QFT-IT may be the preferred test among HCWs with previous TST. In settings where the QFT-IT is not available, appropriate cut-offs for TST reactivity should be evaluated for use among HCWs.

Applicability of in-house loop-mediated isothermal amplification for rapid identification of Mycobacterium tuberculosis complex grown on solid media

A simple, rapid, and low-cost identification method is required in tuberculosis high-burden countries. We report the applicability of in-house loop-mediated isothermal amplification (LAMP) targeting 16S ribosomal RNA for the rapid identification of Mycobacterium tuberculosis complex grown on Lowenstein-Jensen media. Eighty acid-fast staining-positive clinical isolates were selected and used to evaluate the LAMP assay in comparison with polymerase chain reaction and conventional culture-based tests. The LAMP assay identified 60 M. tuberculosis isolates from 80 clinical isolates using simple heat-extracted DNA directly from the colony suspension. The results were in complete agreement with those obtained using the other methods, and the utility of the direct LAMP assay from a colony was demonstrated. The LAMP assay appears to be a practical and low-cost method that can be used for the rapid identification of M. tuberculosis isolates and suitable for endemic low-resource settings.

Rapid identification of Mycobacterium tuberculosis in BACTEC MGIT960 cultures by in-house loop-medicated isothermal amplification

Definitive diagnosis of tuberculosis (TB) by conventional culture, followed by bacterial identification based on biochemical tests is time-consuming and tedious. Simple loop-mediated isothermal amplification (LAMP) specific for Mycobacterium tuberculosis complex, targeting the M. tuberculosis 16S ribosomal RNA gene, termed TB-LAMP, was evaluated as an alternative for rapid culture confirmation. TB-LAMP was assessed for its ability to detect M. tuberculosis complex in BACTEC MGIT 960-positive cultures. Of the 103 cultures evaluated, 100 were identified to contain M. tuberculosis complex by TB-LAMP and had concordant results with standard biochemical tests of niacin accumulation, nitrate reductase, lack of heat-stable catalase, and susceptibility to para-nitrobenzoic acid. These results indicate that TB-LAMP in combination with BACTEC MGIT 960 is a specific, reliable, and technically feasible method for rapid and accurate identification of M. tuberculosis complex.

SNP genotypes of Mycobacterium leprae isolates in Thailand and their combination with rpoT and TTC genotyping for analysis of leprosy distribution and transmission

Based on the discovery of three single nucleotide polymorphisms (SNPs) in Mycobacterium leprae, it has been previously reported that there are four major SNP types associated with different geographic regions around the world. Another typing system for global differentiation of M. leprae is the analysis of the variable number of short tandem repeats within the rpoT gene. To expand the analysis of geographic distribution of M. leprae, classified by SNP and rpoT gene polymorphisms, we studied 85 clinical isolates from Thai patients and compared the findings with those reported from Asian isolates. SNP genotyping by PCR amplification and sequencing revealed that all strains like those in Myanmar were SNP type 1 and 3, with the former being predominant, while in Japan, Korea, and Indonesia, the SNP type 3 was found to be more frequent. The pattern of M. leprae distribution in Thailand and Myanmar is quite similar, except that SNP type 2 was not found in Thailand. In addition, the 3-copy hexamer genotype in the rpoT gene is shared among the isolates from these two neighboring countries. On the basis of these two markers, we postulate that M. leprae in leprosy patients from Myanmar and Thailand has a common historical origin. Further differentiation among Thai isolates was possible by assessing copy numbers of the TTC sequence, a more polymorphic microsatellite locus.