Paucibacillary Specimens Research Articles

Analysis of unsuccessful tests and the effect of prolonged clinical sample preprocessing in the GeneXpert MTB/RIF assay

BackgroundThe GeneXpert MTB/RIF (Xpert) assay is a widely used technology for detecting Mycobacterium tuberculosis (MTB) in clinical samples. However, the study on the failure of the Xpert assay during routine implementation and its potential solutions is limited.MethodsWe retrospectively analyzed the records of unsuccessful tests in the Xpert and the GeneXpert MTB/RIF Ultra (Ultra) assays between April 2017 and April 2021 at the Shanghai Public Health Clinical Center. To further investigate the effect of prolonged preprocessing on clinical sputum, an additional 120 sputum samples were collected for Xpert testing after 15 min, 3 h, and 6 h preprocessing. The analysis was performed by SPSS version 19.0 software.ResultsA total of 11,314 test records were analyzed, of which 268 (2.37%) had unsuccessful test results. Among these, 221 (1.95%) were reported as “Error”, 43 (0.38%) as “Invalid”, and 4 (0.04%) as “No result”. The most common clinical specimen for Xpert tests was sputum, accounting for 114 (2.17%) unsuccessful tests. The failure rate of urine specimens was lower than that of sputum (OR = 0.12, 95% CI: 0.02–0.88, χ2 = 6.22, p = 0.021). In contrast, the failure rate of stool specimens was approximately twice as high as that of sputum (OR = 1.93, 95% CI: 1.09–3.40, χ2 = 5.35, p = 0.014). In the prolonged preprocessing experiment, 102 cases (85%) yielded consistent results in Xpert tests. Furthermore, 7 cases (5.83%) detected an increase in MTB load, 8 cases (6.67%) detected a decrease in MTB load, and 3 cases (2.5%) yielded incongruent results in MTB and rifampicin resistance detection.ConclusionsThe primary cause of unsuccessful tests in the Xpert assay was reported as “Error”. Despite varying failure rates depending on the samples, the Xpert assay can be applied to extrapulmonary samples. For paucibacillary specimens, retesting the remaining preprocessed mixture should be carefully considered.

Evaluation of the GeneXpert MTB/RIF Assay for Rapid Diagnosis of Tuberculosis and Detection of Rifampin Resistance in Tuberculous Patients Admitted to Abbassia Chest Hospital

Abstract Background Tuberculosis is considered one of the major infectious diseases especially in the developing countries and a significant diagnostic and therapeutic challenge worldwide. Gene Xpert MTB/RIF assay is a diagnostic test which depends on a real-time polymerase chain reaction for rapid diagnosis of Mycobacterium Tuberculosis and rifampicin resistance in a single test. Aim To evaluate the diagnostic utility of Gene Xpert MTB/RIF assay for rapid diagnosis of pulmonary and extrapulmonary tuberculosis as well as the detection of rifampin resistance in specimens obtained from suspected tuberculous patients in Abbassia Chest Hospital. Patients and Methods Pulmonary and extrapulmonary samples from 77 cases with suspected TB were collected. All retrieved samples were examined with: direct smear microscopy for AFB, culture for Mycobacterium tuberculosis (L.J. media) along with Drug susceptibility testing (D.S.T.) for positive cultures. As well as the gene Xpert MTB/RIF assay and their results were compared to those of both culture and D.S.T. (as gold standard reference methods). Results Gene Xpert MTB/RIF assay showed the highest sensitivity, negative predictive value (NPV) and diagnostic accuracy in detection of pulmonary TB (96.4, 96.4 and 93.1% respectively), with 90%specificity. Xpert MTB/RIF assay showed the lowest sensitivity in diagnosing TB pleural effusion (66.6%) but with the highest specificity and positive predictive value (PPV) (100% for both). As regards diagnosing TB lymphadenitis, gene Xpert MTB/RIF assay showed 75% sensitivity and the lowest specificity (33.3%). Considering rifampin resistance, gene Xpert MTB/RIF assay showed 100% specificity in detection of RIF- Resistance with variable sensitivity according to the type of TB, being the highest in pulmonary TB (90.9% sensitivity). Conclusion Gene Xpert MTB/RIF assay could be used as the first line diagnostic tool for diagnosis of pulmonary TB because of its high diagnostic yield. Yet, it’s not recommended to replace the culture for diagnosing extrapulmonary TB especially in diagnosing tuberculous pleural effusion (pauci-bacillary specimens) which has limited diagnostic utility. Also, the assay showed 100% specificity in diagnosing rifampicin resistance guiding physicians to justifiably starting second line anti-TB treatment.

Evaluation of Xpert MTB/RIF Ultra assay for detection of Mycobacterium tuberculosis and rifampicin resistance

Tuberculosis (TB) is a public health challenge globally, and molecular testing is recommended to expedite diagnosis. Concerns that Xpert MTB/RIF assay (Xpert) may be less sensitive when testing paucibacillary samples led to the development of the Xpert MTB/RIF Ultra assay (Ultra). We evaluated the performance of Ultra against Xpert on clinical samples sent to the national reference laboratory in Singapore. In total, 149 samples collected between January 2019 and November 2020 were analysed. Mycobacterium tuberculosis complex (MTBC) was isolated from 55 cultures. Using culture as the reference standard, Ultra demonstrated higher sensitivity (96.4% vs 85.5%) and marginally lower specificity (88.3% vs 89.4%) compared to Xpert in the full cohort. When considering only paucibacillary specimens such as extrapulmonary and smear-negative samples, similar results were obtained. Reclassifying Ultra trace results (low levels of MTB are detected but no rifampicin resistant result is detected) as negative in the full cohort led to a decrease in sensitivity by 10.9% and a marginal increase in specificity by 1.1%. In instances of low bacillary load, Ultra also identified rifampicin resistance more accurately than Xpert, when corroborated against other methods such as broth microdilution, line probe assay and whole genome sequencing (WGS). One isolate tested rifampicin-resistant using Xpert and Ultra, but was phenotypically susceptible and WGS demonstrated the presence of the silent mutation Thr444Thr. Ultra is more sensitive than Xpert in the detection of MTBC and rifampicin resistance in our local setting. Nevertheless, the results of molecular testing should still be correlated with phenotypic studies.

Utility of Multi-target Nested PCR and ELISPOT Assays for the Detection of Paucibacillary Leprosy: A Possible Conclusion of Clinical Laboratory Misdiagnosis.

The diagnosis of paucibacillary (PB) leprosy often possesses a diagnostic challenge, especially for pure neuritic and lesser skin lesions with the zero bacillary load, requiring a sensitive and accurate diagnostic tool. We have included 300 clinically diagnosed new leprosy cases (comprising 98 PB cases) and analyzed the sensitivity and specificity of PB leprosy cases by nested PCR with folP, gyrA, rpoB, RLEP, and 16SrRNA and Enzyme-linked Immunospot Assay test (ELISPOT) with MMPII, NDO-BSA, and LID-1 antigens by detecting interferon gamma (IFN-γ) release. The overall positivity rates of genes tested in 300 clinical specimens were identified as 55% of 16SrRNA, 59% of RLEP, 59.3% of folP, 57.3% of rpoB, 61% of gyrA while 90% of nested folP, 92.6% of nested rpoB, and 95% of nested gyrA, and 285 (95%) of at least one gene positive cases. For PB specimens, 95% PCR positivity was achieved by three tested genes in nested PCR. The data obtained from ELISPOT for three antigens were analyzed for IFN-γ expression with 600 subjects. Among 98 PB leprosy cases, the sensitivity of MMP II, LID-1, and NDO-BSA was 90%, 87%, and 83%, respectively, and the specificity was 90%, 91%, and 86%, respectively. The total number of cases positive for at least one antigen was 90 (91.8%) in PB, which is significantly higher than that in multibacillary (MB) leprosy (56.7%). The combination of multi-targets nested PCR and ELISPOT assay provides a specific tool to early clinical laboratory diagnosis of PB leprosy cases. The two assays are complementary to each other and beneficial for screening PB patients.

Comparison of Polymerase Chain Reaction With Fluorescent Microscopy for Detecting Pulmonary Tuberculosis in Smear-Negative Sputum Samples in Quetta, Pakistan

Background: One of the common clinical manifestations of extra-pulmonary tuberculosis is tuberculous meningitis (TBM). New methods, which are simple and effective, are necessary for early diagnosis of TBM. Objective: This study aimed to assess the use of fluorescence microscopy and polymerase chain reaction (PCR) techniques targeting pncA and IS6110. PCR is a fast and reliable technique for diagnosing tuberculosis (TB), particularly in paucibacillary specimens such as smear-negative sputum for diagnosing patients with Mycobacterium tuberculosis. Materials and Methods: The pncA and IS6110 multiplex-PCR methods were applied to analyze sputum using a specific pair of primers designed to amplify the insertion sequence, pncA, and IS6110 in the M. tuberculosis genome. A total of 200 sputum samples were collected from patients with TB. Out of 200 patients, 54.0% (n=108) and 46.0% (n=92) were males and females at Fatima Jinnah General and Chest Hospital, Quetta, respectively. Results: M. tuberculosis was detected as 15 (16.3%) and 18 (16.7%) for pncA and IS6110 using PCR and fluorescence microscopy, respectively. M. tuberculosis DNA detected by PCR and smear-negative fluorescence microscopy was 16.50% (n=33) and 14.70% (n=18), respectively. In other words, PCR assay detected the increased prevalence of M. tuberculosis. Risk factors revealed high exposure to receiving TB infection which was associated with urban areas (OR=1.07, 95% CI: 0.34–3.35), TB in family (OR=1.22, 95% CI: 0.38-3.88), over crowdedness (OR=2.93, 95% CI: 0.37-23.7), malnutrition (OR: 1.39; 95% CI: 0.52-3.74), and rural areas (OR: 1.54, 95% CI: 0.72-3.31). Conclusion: A wide range of molecular assays are now being developed and reviewed for detecting TB. We conclude that the use of pncA and IS6110 PCR assays is beneficial in the quick diagnosis of TB meningitis.

Xpert MTB/RIF Ultra and Xpert MTB/RIF assays for extrapulmonary tuberculosis and rifampicin resistance in adults.

Xpert MTB/RIF Ultra and Xpert MTB/RIF assays for extrapulmonary tuberculosis and rifampicin resistance in adults.

Performance of Xpert MTB/RIF Ultra assay on respiratory and extra-respiratory samples in a high-resource setting with a low tuberculosis prevalence

The Xpert MTB/RIF assay is a molecular assay that has improved the detection of tuberculosis and rifampicin resistance. However, its sensitivity is limited in patients with paucibacillary disease. Xpert MTB/RIF Ultra has been developed to resolve this limitation. We compared the performance of Xpert Ultra with that of culture for detection of Mycobacterium tuberculosis and rifampicin resistance. We reviewed laboratory records for 848 respiratory and 419 extrarespiratory samples that were processed between April 2018 and October 2019. The sensitivity, specificity, negative predictive value, and positive predictive value of Xpert Ultra were 94.8%, 98%, 98.8%, and 91.3% for respiratory samples and 83.8%, 96.9%, 98.4% and 72.1% for nonrespiratory ones. We found 26 culture-negative/Ultra-positive samples. Most of them have low bacillary burden and more than half belonged to patients with history of tuberculosis. Xpert Ultra demonstrates excellent diagnostic accuracy for tuberculosis detection, including paucibacillary specimens. In patients with history of tuberculosis, PCR results should be interpreted carefully.

Xpert MTB/RIF ultra for rapid diagnosis of extrapulmonary tuberculosis in a high-income low-tuberculosis prevalence setting

The diagnosis of extrapulmonary tuberculosis (EPTB) is often challenging due to paucibacillary nature of the disease. Xpert MTB/RIF Ultra (Ultra) has been developed to improve detection of Mycobacterium tuberculosis complex (MTC) in paucibacillary specimens. The objective of the study was to assess the performance of Ultra for the diagnosis of EPTB in a high-income low TB prevalence country. Extrapulmonary samples received for TB diagnostics at two hospitals in Norway between January 2015 and January 2016 were prospectively and consecutively included. Defrosted samples were subjected to Ultra. Culture and routine PCR tests were used as reference standard. A total of 82 samples, 10 culture and/or routine PCR positive (confirmed TB) samples and 72 culture and routine PCR negative samples were included in analysis. The overall sensitivity and specificity of Ultra were 90% (9/10, 95% CI 56–100) and 99% (71/72, 95% CI 93–100), respectively. Ultra was positive in 6/7 smear negative confirmed TB samples. To conclude, Ultra showed a high sensitivity and specificity in extrapulmonary specimens and may contribute to a rapid diagnosis of EPTB in a low TB prevalence setting.

Detection of Mycobacterium tuberculosis in paucibacillary sputum: performances of the Xpert MTB/RIF ultra compared to the Xpert MTB/RIF, and IS6110 PCR

The Xpert MTB/RIF Ultra assay has recently been launched to improve the detection of smear negative disease. This retrospective study compares the sensitivity of Xpert MTB/RIF Ultra with that of Xpert MTB/RIF tests and IS6110 real-time PCR in sputum. Diagnostic performance of three molecular tests was evaluated using 48 culture-positive clinical respiratory specimens diluted to obtain paucibacillary sputum specimens. Xpert MTB/RIF Ultra had the highest sensitivity of 100% compared to 42% (P < 0.001) for Xpert MTB/RIF and 64.5% (P = 0.02) for IS6110-PCR. All “very low” or “low” positive specimens using Xpert MTB/RIF Ultra were tested positive using IS6110-PCR, but 35.4% were found negative using Xpert MTB/RIF. Xpert MTB/RIF Ultra is more sensitive than the two other tests for sputum with a low bacterial load. Adding detection of IS6110 and IS1081 to rpoB, is a key evolution of the assay and improves the detection of Mycobacterium tuberculosis' DNA in paucibacillary sputum.

Commercial products to preserve specimens for tuberculosis diagnosis: a systematic review

Eliminating tuberculosis in high-burden settings requires improved diagnostic capacity. Important tests such as Xpert® MTB/RIF and culture are often performed at centralised laboratories that are geographically distant from the point of specimen collection. Preserving specimen integrity during transportation, which could affect test performance, is challenging. To conduct a systematic review of commercial products for specimen preservation for a World Health Organization technical consultation. Databases were searched up to January 2018. Methodological quality was assessed using Quality Assessment of Technical Studies, a new technical study quality-appraisal tool, and Quality Assessment of Diagnostic Accuracy Studies-2. Studies were analysed descriptively in terms of the different products, study designs and diagnostic strategies used. Four products were identified from 16 studies: PrimeStore-Molecular-Transport-Medium (PS-MTM), FTA card, GENO•CARD (all for nucleic acid amplification tests [NAATs]) and OMNIgene•SPUTUM (OMS; culture, NAATs). PS-MTM, but not FTA card or GENO•CARD, rendered Mycobacterium tuberculosis non-culturable. OMS reduced Löwenstein-Jensen but not MGIT™ 960™ contamination, led to delayed MGIT time-to-positivity, resulted in Xpert performance similar to cold chain-transported untreated specimens, and obviated the need for N-acetyl-L-cysteine-sodium hydroxide decontamination. Data from paucibacillary specimens were limited. Evidence that a cold chain improves culture was mixed and absent for Xpert. The effect of the product alone could be discerned in only four studies. Limited evidence suggests that transport products result in test performance comparable to that seen in cold chain-transported specimens.

Rapid and specific detection of Mycobacterium tuberculosis directly from sputum specimens using IS6110 and pncA through multiplex-PCR

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis complex, is the second leading cause of death. One third of the world’s population is infected with TB. Every day more than 23000 people develop active TB and nearly 5000 die. Approximately 20-50% of patients with TB are smear negative, accounting for as much as 17% of TB transmission, posing an important public health hazard. In the objective of improved TB diagnosis and rapid detection of M. tuberculosis complex species particularly from paucibacillary sputum specimens, the sensitivity of Polymerase Chain Reaction (PCR) using IS6110 and pncA as genetic targets was compared with the conventional fluorescent microscopy. The study also aimed to check the sensitivity of two different genetic markers IS6110 and pncA for the detection of M. tuberculosis. Sputum specimens were collected from TB suspected subjects (N= 200; males=108; females=92; mean age=47±18.4) attending outpatient department at Fatima Jinnah General and Chest Hospital, Quetta. All the samples were decontaminated using N-acetyl-L-cysteine (NALC)-NaOH method and were subjected to auramine-O fluorescent microscopy and multiplex PCR using TB1 and TB2 primers specific for M. tuberculosis complex and pncATB-1.2 and pncAMT-2 primers specific to M. tuberculosis. Out of 200 specimens, M. tuberculosis around 15 (7.5%) was detected by fluorescent microscopy and 33 (16.5%) were detected through PCR, respectively. Whereas 18 smear negative specimens were found to be positive by PCR. Statistically significant difference between fluorescent microscopy and PCR was observed (p 0.05). Similarly, age was not found to be associated (p>0.05) with the increased risk of TB, however, the disease incidence was more prevalent (20.89%) in patients aged 41–60 years. Multiplex PCR showed increased sensitivity as compared to fluorescent microscopy for TB diagnosis and will bea useful tool in detecting smears negative TB. Further, it can also be concluded that both genetic markers IS6110 and pncA showed similar sensitivity in the detection of M. tuberculosis. Keywords: Quetta; Tuberculosis; Paucibacillary; Diagnosis; Genetic markers http://dx.doi.org/10.19045/bspab.2017.60052

Comparative evaluation of loop-mediated isothermal amplification and conventional methods to diagnose extrapulmonary tuberculosis

Background: Extra-pulmonary tuberculosis is difficult to diagnose by conventional methods, because they are less sensitive and more time consuming. Loop-mediated Isothermal Amplification (LAMP) is a novel gene amplification method that has been developed to diagnose Mycobacterium tuberculosis complex in pulmonary and paucibacillary extrapulmonary specimens even in resource poor settings. Aims and Objectives: To evaluate the sensitivity and specificity of LAMP to detect Mycobacterium tuberculosis complex in paucibacillary extra-pulmonary specimens and to compare the results with other conventional methods in extrapulmonary specimens. Materials and Methods: 45 specimens from suspected extrapulmonary tuberculosis patients were collected and tested by LAMP method after DNA extraction. Simultaneously, these specimens were tested by smear microscopy, solid and liquid culture methods. Culture positivity, either in solid or liquid culture, was considered as a confirmed case of extrapulmonary tuberculosis. Results: Sensitivity of LAMP was 95.6% whereas for liquid culture, solid culture and smear microscopy were 69.6%, 65.2% and 17.4% respectively. Specificity for LAMP was 95.4% and for other 3 conventional methods were 100%. Positive predictive values, negative predictive values and likelihood ratios were also evaluated. Turn-around time (TAT) for LAMP was 8 hours only whereas for liquid culture was 2-4 weeks, and for solid culture it was 4-8 weeks. Conclusion: LAMP was a simple, rapid and cost-effective procedure with good sensitivity and specificity. It was found to be better than conventional methods to diagnose extrapulmonary tuberculosis.

Use of amplified Mycobacterium tuberculosis direct test in respiratory samples from HIV-infected patients in Brazil

OBJECTIVE: To compare the accuracy of the amplified Mycobacterium tuberculosis direct (AMTD) test with reference methods for the laboratory diagnosis of tuberculosis in HIV-infected patients. METHODS: This was a study of diagnostic accuracy comparing AMTD test results with those obtained by culture on Löwenstein-Jensen (LJ) medium and by the BACTEC Mycobacteria Growth Indicator Tube 960 (BACTEC MGIT 960) system in respiratory samples analyzed at the Bioassay and Bacteriology Laboratory of the Oswaldo Cruz Foundation Evandro Chagas Clinical Research Institute in the city of Rio de Janeiro, Brazil. RESULTS: We analyzed respiratory samples collected from 118 patients, of whom 88 (74.4%) were male. The mean age was 36.6 ± 10.6 years. Using the AMTD test, the BACTEC MGIT 960 system, and LJ culture, we identified M. tuberculosis complex in 31.0%, 29.7%, and 27.1% of the samples, respectively. In comparison with LJ culture, the AMTD test had a sensitivity, specificity, positive predictive value, and negative predictive value of 87.5%, 89.4%, 75.7%, and 95.0%, respectively, for LJ culture, whereas, in comparison with the BACTEC MGIT 960 system, it showed values of 88.6%, 92.4%, 83.8%, and 94.8%, respectively. CONCLUSIONS: The AMTD test showed good sensitivity and specificity in the population studied, enabling the laboratory detection of M. tuberculosis complex in paucibacillary respiratory specimens.

Application of RLEP Real-Time PCR for Detection of M. leprae DNA in Paraffin-Embedded Skin Biopsy Specimens for Diagnosis of Paucibacillary Leprosy

The TaqMan real-time polymerase chain reaction (PCR) assay was evaluated systematically with respect to the standard curve, linear range, and used for detecting Mycobacterium leprae DNA in paraffin-embedded skin biopsy specimens from 60 confirmed leprosy patients and three healthy individuals and 29 other dermatoses and bacterial DNA from 21 different species. The test was further evaluated with 51 paucibacillary (PB) patients. The results showed that the test had good sensitivity (8 fg) and good specificity with no cross-reactivity with 21 other bacterial species and the control specimens, except one with Xanthomatosis. The real-time PCR detection rate for the 51 PB specimens was 74.5% (38 of 51). We conclude that the real-time PCR test is a useful adjunct test for diagnosing early stage or PB leprosy cases.

Tuberculosis: epidemiological profile in a reference hospital in the treatment of disease

Objective: This cross-sectional descriptive study aimed to determine the epidemiological, clinical and diagnosis of patients with mycobacteria between March 2008 and February 2010, in Juiz de Fora, Minas Gerais State. Methods: Data collection was performed at the medical records and patients. Results: In 175 cases, 170 with Mycobacterium tuberculosis, two M. tuberculosis/M. avium complex, two M. avium complex and one M. bovis/M. tuberculosis. 75.4% of cases in male patients, meian age 40 years, 14.3% in HIV positive, 32% with low family income and poor housing. Pulmonary disease occurred in 94.9%. 45.1% were cured, 24.0% abandoned the treatment and 9.7% died. Supervision of treatment occurred in 60% of cases and 56% of cases was tested for HIV. 9.6% of paucibacillary specimens and 55.5% of extrapulmonary TB the diagnosis was possible only by culture. Conclusion: Was a clear predominance of the disease in male patients with pulmonary tuberculosis. The treatment was partially observed and several pacients with no known diagnosis of HIV. The use of mycobacterial culture was an important diagnostic tool, complementary to smear.

Nipple discharge: An uncommon presentation of a common disease, Tuberculosis

Sir, The incidence of tuberculosis is quite high in our country and, consequently, tuberculosis of breast may be frequent enough but possibly overlooked or misdiagnosed as carcinoma or pyogenic abscess. [1] The most common mode of spread to the breast is lymphatic and hematogenous, although spread from contagious structures, direct inoculation and ductal infection are other rare modes of spread of this disease. [2] Tubercular mastitis can present as nodulocaseous, disseminated and breast abscess. [2] Moreover, superadded bacterial infection further causes misdiagnosis of this disease as pyogenic abscess. Acid fast bacilli (AFB) microscopy and culture is considered as the gold standard for the diagnosis of tuberculosis, although paucibacillary specimens and time required for culture are important limitations. Fine needle aspiration has also been advocated as an important diagnostic tool in breast tuberculosis, but secondary bacterial infection can often be misleading. [1] The advent of newer diagnostic techniques such as automated mycobacterial growth systems (BACTEC) and nucleic acid amplification have been explored as time saving and sensitive techniques. The management of this disease depends on sound diagnosis and anti‑tubercular therapy, with surgery having a minimal role. [1,3]

TRICORE, a novel bead-based specimen concentration method for the culturing of Mycobacterium tuberculosis

Centrifugation is a necessary concentrating step for the detection of Mycobacterium tuberculosis in a liquid culture. However, centrifugation is biologically hazardous and presents an obstacle in the development of an automated culture system. A bead-based bacterial concentration method, TRICORE, was recently developed by Genetein Co., Ltd. We compared the efficacy of TRICORE and conventional centrifugation for concentrating M. tuberculosis in clinical sputum specimens by using liquid and solid culture systems. Among 90 pretreated clinical sputum specimens, 51 (57.3%) and 55 (61.8%) M. tuberculosis isolates were recovered by the MGIT culture system by using the centrifugation and TRICORE methods, respectively (chi‐square test, p=0.5413). The detection time for the centrifugation method was 359.3±117.0h, while that for the bead-based concentration method was 377.6±162.3h (p=0.5637). However, the number of colonies recovered on solid media were significantly higher with the TRICORE method (p=0.003). In particular, among the smear-negative specimens, culture positivity of the TRICORE method was 39.6%, while that of the centrifugation method was 15.1%. The TRICORE bead-based concentration method was considered equivalent to centrifugation and enabled efficient collection of paucibacillary specimens in solution. Thus, the new noncentrifugation concentration method could yield more positive culture results.

Evaluation of bleach-sedimentation for sterilising and concentrating Mycobacterium tuberculosis in sputum specimens

BackgroundBleach-sedimentation may improve microscopy for diagnosing tuberculosis by sterilising sputum and concentrating Mycobacterium tuberculosis. We studied gravity bleach-sedimentation effects on safety, sensitivity, speed and reliability of smear-microscopy.MethodsThis blinded, controlled study used sputum specimens (n = 72) from tuberculosis patients. Bleach concentrations and exposure times required to sterilise sputum (n = 31) were determined. In the light of these results, the performance of 5 gravity bleach-sedimentation techniques that sterilise sputum specimens (n = 16) were compared. The best-performing of these bleach-sedimentation techniques involved adding 1 volume of 5% bleach to 1 volume of sputum, shaking for 10-minutes, diluting in 8 volumes distilled water and sedimenting overnight before microscopy. This technique was further evaluated by comparing numbers of visible acid-fast bacilli, slide-reading speed and reliability for triplicate smears before versus after bleach-sedimentation of sputum specimens (n = 25). Triplicate smears were made to increase precision and were stained using the Ziehl-Neelsen method.ResultsM. tuberculosis in sputum was successfully sterilised by adding equal volumes of 15% bleach for 1-minute, 6% for 5-minutes or 3% for 20-minutes. Bleach-sedimentation significantly decreased the number of acid-fast bacilli visualised compared with conventional smears (geometric mean of acid-fast bacilli per 100 microscopy fields 166, 95%CI 68-406, versus 346, 95%CI 139-862, respectively; p = 0.02). Bleach-sedimentation diluted paucibacillary specimens less than specimens with higher concentrations of visible acid-fast bacilli (p = 0.02). Smears made from bleach-sedimented sputum were read more rapidly than conventional smears (9.6 versus 11.2 minutes, respectively, p = 0.03). Counting conventional acid-fast bacilli had high reliability (inter-observer agreement, r = 0.991) that was significantly reduced (p = 0.03) by bleach-sedimentation (to r = 0.707) because occasional strongly positive bleach-sedimented smears were misread as negative.ConclusionsGravity bleach-sedimentation improved laboratory safety by sterilising sputum but decreased the concentration of acid-fast bacilli visible on microscopy, especially for sputum specimens containing high concentrations of M. tuberculosis. Bleach-sedimentation allowed examination of more of each specimen in the time available but decreased the inter-observer reliability with which slides were read. Thus bleach-sedimentation effects vary depending upon specimen characteristics and whether microscopy was done for a specified time, or until a specified number of microscopy fields had been read. These findings provide an explanation for the contradictory results of previous studies.

Evaluation of rapid techniques for the detection of mycobacteria in sputum with scanty bacilli or clinically evident, smear negative cases of pulmonary and extra-pulmonary tuberculosis

The objective of the current study was to compare two rapid methods, the BBL Mycobacteria Growth Indicator Tube (MGIT TM) and Biotec FASTPlaque TB TM (FPTB) assays, with the conventional Löwenstein-Jensen (LJ) media assay to diagnose mycobacterial infections from paucibacillary clinical specimens. For evaluation of the clinical utility of the BBL MGIT TM and FPTB assays, respiratory tract specimens (n = 208), with scanty bacilli or clinically evident, smear negative cases and non-respiratory tract specimens (n = 119) were analyzed and the performance of each assay was compared with LJ media. MGIT and FPTB demonstrated a greater sensitivity (95.92% and 87.68%), specificity (94.59% and 98.78%), positive predictive value (94.91% and 99.16%) and negative predictive value (96.56% and 90.92%), respectively, compared to LJ culture for both respiratory tract and non-respiratory tract specimens. However, the FPTB assay was unable to detect nontuberculous mycobacteria and few Mycobacterium tuberculosis complex cases from paucibacillary clinical specimens. It is likely that the analytical sensitivity of FPTB is moderately low and may not be useful for the direct detection of tuberculosis in paucibacillary specimens. The current study concluded that MGIT was a dependable, highly efficient system for recovery of M. tuberculosis complexes and nontuberculous mycobacteria from both respiratory and non-respiratory tract specimens in combination with LJ media.

Comparison of the Xpert MTB/RIF Test with an IS 6110 -TaqMan Real-Time PCR Assay for Direct Detection of Mycobacterium tuberculosis in Respiratory and Nonrespiratory Specimens

The sensitivities of the Xpert MTB/RIF test and an in-house IS6110-based real-time PCR using TaqMan probes (IS6110-TaqMan assay) for the detection of Mycobacterium tuberculosis complex (MTBC) DNA were compared by use of 117 clinical specimens (97 culture positive and 20 culture negative for MTBC) that were frozen in sediment. The 97 clinical specimens included 60 respiratory and 37 nonrespiratory specimens distributed into 36 smear-positive and 61 smear-negative specimens. Among the 97 culture-positive specimens, 4 had rifampin-resistant isolates. Both methods were highly specific and exhibited excellent sensitivity (100%) with smear-positive specimens. The sensitivity of the Xpert MTB/RIF test with the whole smear-negative specimens was more reduced than that of the IS6110-TaqMan assay (48 versus 69%, P = 0.005). Both methods exhibited similar sensitivities with smear-negative respiratory specimens, but the Xpert MTB/RIF test had lower sensitivity with smear-negative nonrespiratory specimens than the IS6110-TaqMan assay (37 versus 71%, P = 0.013). Finally, the sensitivities of the Xpert MTB/RIF test and the IS6110-TaqMan assay were 79% and 84%, respectively, with respiratory specimens and 53% and 78%, respectively (P = 0.013), with nonrespiratory specimens. The Xpert MTB/RIF test correctly detected the rifampin resistance in smear-positive specimens but not in the one smear-negative specimen. The Xpert MTB/RIF test is a simple rapid method well adapted to a routine laboratory that appeared to be as sensitive as the IS6110-TaqMan assay with respiratory specimens but less sensitive with paucibacillary specimens, such as smear-negative nonrespiratory specimens.