Performance of Mycobacterium Growth Indicator Tube BACTEC 960 with Lowenstein-Jensen method for diagnosis of Mycobacterium tuberculosis at Ethiopian National Tuberculosis Reference Laboratory, Addis Ababa, Ethiopia

Diagnostic accuracy, feasibility and acceptability of stool-based testing for childhood tuberculosis

Background

Childhood tuberculosis (TB) diagnosis remains challenging, partly because children cannot provide sputum. This study evaluated the diagnostic accuracy of the Simple One-Step (SOS) stool method with Xpert MTB/RIF Ultra (Xpert-Ultra) for childhood TB compared to culture and Xpert-Ultra on a respiratory sample (RS) and clinical diagnosis. It also assessed the feasibility and acceptability of stool testing according to laboratory staff, and caregivers' sample preference.

Methods

We enrolled children (≤10 years) with presumptive pulmonary tuberculosis in Ethiopia. RS was tested using Xpert-Ultra and culture; stool samples were tested using the SOS stool method with Xpert-Ultra. Laboratory staff and caregivers' opinions were assessed using standardised questionnaires.

Results

Of the 898 children enrolled, 792, 832 and 794 were included for assessing the diagnostic accuracy of SOS stool with Xpert-Ultra against culture, RS Xpert-Ultra and clinical diagnosis, respectively, yielding sensitivity estimates for SOS stool with Xpert-Ultra of 69.1% (95% confidence interval (CI) 56.0-79.7%), 76.8% (95% CI 64.2-85.9%) and 59.0% (95% CI 47.9-69.2%), respectively. The specificity was ≥98.8% for all comparisons. The rate of non-determinate test results was 2.8% after one repeat test. According to laboratory staff, stool collection was feasible and acceptable and the SOS stool method was easy to perform. Most caregivers (75%) preferred stool for TB diagnosis over RS.

Conclusion

This study shows that SOS stool Xpert-Ultra testing offers a good alternative to RS testing for TB in children who cannot spontaneously produce a sputum sample and would otherwise need to undergo invasive procedures to obtain RS for diagnosis.

Evaluating the Sensitivity of Different Molecular Techniques for Detecting Mycobacterium tuberculosis Complex in Patients with Pulmonary Infection

This study aimed to evaluate the accuracy of detecting drug-resistant Mycobacterium tuberculosis complex (MTBC)-specific DNA in sputum specimens from 48 patients diagnosed with pulmonary tuberculosis. The presence of MTBC DNA in the specimens was validated using the GeneXpert MTB/RIF system and compared with a specific PCR assay targeting the IS6110 and the mtp40 gene sequence fragments. Additionally, the results obtained by multiplex PCR assays to detect the most frequently encountered rifampin, isoniazid, and ethambutol resistance-conferring mutations were matched with those obtained by GeneXpert and phenotypic culture-based drug susceptibility tests. Of the 48 sputum samples, 25 were positive for MTBC using the GeneXpert MTB/RIF test. Nevertheless, the IS6110 and mtp40 single-step PCR revealed the IS6110 in 27 of the 48 sputum samples, while the mtp40 gene fragment was found in only 17 of them. Furthermore, multiplex PCR assays detected drug-resistant conferring mutations in 21 (77.8%) of the 27 samples with confirmed MTBC DNA, 10 of which contained single drug-resistant conferring mutations towards ethambutol and two towards rifampin, and the remaining nine contained double-resistant mutations for ethambutol and rifampin. In contrast, only five sputum specimens (18.5%) contained drug-resistant MTBC isolates, and two contained mono-drug-resistant MTBC species toward ethambutol and rifampin, respectively, and the remaining three were designated as multi-drug resistant toward both drugs using GeneXpert and phenotypic culture-based drug susceptibility tests. Such discrepancies in the results emphasize the need to develop novel molecular tests that associate with phenotypic non-DNA-based assays to improve the detection of drug-resistant isolates in clinical specimens in future studies.

Evaluation of the Cepheid 3-gene host response blood test for tuberculosis diagnosis and treatment response monitoring in a primary-level clinic in rural China

A rapid, accurate, non-sputum-based triage test for diagnosing tuberculosis (TB) is a high-priority need. Cepheid developed a novel prototype blood test, Xpert Mycobacterium tuberculosis Host Response (Xpert-MTB-HR), which generates a TB score based on the mRNA expression of three genes. We conducted a case-control study with prospective recruitment to evaluate its accuracy in the clinic of the Wusheng County Centers for Disease Prevention and Control in China. We enrolled 149 TB patients, 248 other respiratory diseases (ORD) patients, and 193 healthy controls. In addition, whole-blood samples taken from TB patients after 2, 5, and 6 months of treatment were tested with Xpert-MTB-HR to evaluate its ability to monitor treatment response. Xpert-MTB-HR discriminated between TB and healthy controls with an area under the curve (AUC) of 0.912 (95% CI, 0.878-0.945). With the specificity of 70% envisioned for a triage test, its sensitivity was 90.1% (84.9%-94.6%). Xpert-MTB-HR discriminated between TB and ORD with an AUC of 0.798 (0.750-0.847), and at specificity of 70%, the sensitivity was only 75.8% (68.5%-82.8%). In patients determined by Ultra to have medium or high sputum bacillary loads, with specificity of 70%, the sensitivity for discriminating patients with TB from healthy controls was 100.0% (100.0-100.0) and from patients with ORD, 95.1% (89.8-100.0). The TB scores generally increased by 2 months of treatment and then remained stable. Xpert-MTB-HR met the criteria for a triage test to discriminate between TB and healthy controls, but not between TB and ORD, except when limited to patients with high sputum bacillary loads. Xpert-MTB-HR showed promise for monitoring response to treatment but needs to be further evaluated in larger prospective studies.

Xpert MTB/RIF Ultra on contaminated liquid cultures for tuberculosis and rifampicin-resistance detection: a diagnostic accuracy evaluation

BACKGROUND

Xpert MTB/RIF Ultra (Ultra) is a widely used rapid front-line tuberculosis and rifampicin-susceptibility testing. Mycobacterium Growth Indicator Tube (MGIT) 960 liquid culture is used as an adjunct but is vulnerable to contamination. We aimed to assess whether Ultra can be used on to-be-discarded contaminated cultures.

METHODS

We stored contaminated MGIT960 tubes (growth-positive, acid-fast bacilli [AFB]-negative) originally inoculated at a high-volume laboratory in Cape Town, South Africa, to diagnose patients with presumptive pulmonary tuberculosis. Patients who had no positive tuberculosis results (smear, Ultra, or culture) at contamination detection and had another, later specimen submitted within 3 months of the contaminated specimen were selected. We evaluated the sensitivity and specificity of Ultra on contaminated growth from the first culture for tuberculosis (next-available non-contaminated culture result reference standard) and rifampicin resistance (vs MTBDRplus on a later isolate). We calculated potential time-to-diagnosis improvements and also evaluated the immunochromatographic MPT64 TBc assay.

FINDINGS

Between June 1 and Aug 31, 2019, 36 684 specimens from 26 929 patients were processed for diagnostic culture. 2402 (7%) cultures from 2186 patients were contaminated. 1068 (49%) of 2186 patients had no other specimen submitted. After 319 exclusions, there were 799 people with at least one repeat specimen submitted; of these, we included in our study 246 patients (31%) with a culture-positive repeat specimen and 429 patients (54%) with a culture-negative repeat specimen. 124 patients (16%) with a culture-contaminated repeat specimen were excluded. When Ultra was done on the initial contaminated growth, sensitivity was 89% (95% CI 84-94) for tuberculosis and 95% (75-100) for rifampicin-resistance detection, and specificity was 95% (90-98) for tuberculosis and 98% (93-100) for rifampicin-resistance detection. If our approach were used the day after contamination detection, the time to tuberculosis detection would improve by a median of 23 days (IQR 13-45) and provide a result in many patients who had none. MPT64 TBc had a sensitivity of 5% (95% CI 0-25).

INTERPRETATION

Ultra on AFB-negative growth from contaminated MGIT960 tubes had high sensitivity and specificity, approximating WHO criteria for sputum test target product performance and exceeding drug susceptibility testing. Our approach could mitigate negative effects of culture contamination, especially when repeat specimens are not submitted.

FUNDING

The European & Developing Countries Clinical Trials Partnership, National Institutes of Health.

Antibodies against native proteins of Mycobacterium tuberculosis can detect pulmonary tuberculosis patients

Accurate point-of-care testing (POCT) is critical for managing tuberculosis (TB). However, current antibody-based diagnosis shows low specificity and sensitivity. To find proper antigen candidates for TB diagnosis by antibodies, we assessed IgGs responsiveness to Mycobacterium tuberculosis proteins in pulmonary TB (PTB) patients. We employed major secreted proteins, such as Rv1860, Ag85C, PstS1, Rv2878c, Ag85B, and Rv1926c that were directly purified from M. tuberculosis. In the first screening, we found that IgG levels were significantly elevated in PTB patients only against Rv1860, PstS1, and Ag85B among tested antigens. However, recombinant PstS1 and Ag85B from Escherichia coli (E. coli) couldn't distinguish PTB patients and healthy controls (HC). Recombinant Rv1860 was not checked due to its little expression. Then, the 59 confirmed PTB patients from Soetomo General Academic Hospital, Surabaya, Indonesia, and 102 HC were tested to Rv1860 and Ag85B only due to the low yield of the PstS1 from M. tuberculosis. The ROC analysis using native Ag85B and Rv1860 showed an acceptable area under curve for diagnosis, which is 0.812 (95% CI 0.734-0.890, p < 0.0001) and 0.821 (95% CI 0.752-0.890, p < 0.0001). This study indicates that taking consideration of native protein structure is key in developing TB's POCT by antibody-based diagnosis.

Comparative serum lipid and immunohematological values among adult pulmonary tuberculosis and tuberculosis lymphadenitis cases and their association with sputum bacilli load and time to culture positivity in Northwestern Ethiopia

BACKGROUND

The serum lipid and immunohematological values of tuberculosis lymphadenitis (TBLN) patients is poorly documented relative to pulmonary tuberculosis (PTB) cases. Therefore, the aim of this study was to investigate the serum lipid and immunohematological values of patients with TBLN in comparison with PTB (PTB) patients.

METHODS

An institution-based comparative cross-sectional study was conducted in Northwest Ethiopia from March to December 2021. The study participants were bacteriologically confirmed PTB (n = 82) and TBLN (n = 94) cases with no known comorbidity and whose ages was greater than 18 years and with no current pregnancy. Independent sample t-test, one-way ANOVA, box plot, and correlation matrix were used to analyze the data.

RESULTS

The body mass index (BMI), CD4 + T cell count, and high-density lipoprotein-Cholesterol (HDL-C) values were significantly higher among TBLN cases compared with PTB cases. Additionally, the total white blood cell (WBC) count, hemoglobin (Hb), total Cholesterol (CHO) and creatinine (Cr) values were relatively higher among TBLN than PTB (P > 0.05). On the reverse, the platelet count and triacylglycerol (TAG) values were relatively higher among PTB than in TBLN cases. While the mean days of culture positivity were 11.6 days for TBLN, the mean days of culture positivity were 14.0 days for PTB. Anemia and serum lipid values showed no correlation with sputum bacilli load and time to culture positivity.

CONCLUSION

Tuberculous lymphadenitis patients were well-endowed with serum lipid, immunological and nutritional status compared with PTB cases. Hence, the high incidence rate of TBLN in Ethiopia could not be explained by low peripheral immunohematological values, malnutrition, Anemia, and dyslipidemia. Further study for identifying the predictors for TBLN in Ethiopia is highly desirable.

Comparison of Sputum Treated with Power Ultrasound and Routine NALC-NaOH Methods for Mycobacterial Culture: A Prospective Study

Mycobacterial culture remains the gold standard for the diagnosis of active tuberculosis. However, an appropriate digestion and decontamination method is essential for the effective recovery of tubercle bacilli in culture. The study was designed to compare the efficacy of sputum treated with power ultrasound (PU) and routine NALC-NaOH methods for mycobacterial culture from clinically suspected cases of pulmonary tuberculosis. To evaluate the PU and routine NALC-NaOH methods, sputum specimens (n = 597) were studied (culturing on MGIT 960), and the performances were compared. Of the 597 samples, 89 (14.91%) sputum samples treated with the NaOH-NALC method were mycobacterial culture positive, including Mycobacterium tuberculosis (M.TB; n = 77, 12.90%) and nontuberculous mycobacteria (NTM; n = 12, 2.01%). One hundred and ten (18.43%) sputum samples treated with the PU method were culture positive, including M.TB (n = 87, 14.57%) and NTM (n = 23, 3.85%). The PU method detected 10 additional cases of M.TB and 11 additional cases of NTM when compared to the NALC-NaOH method. Statistical analysis showed that a significant difference was found in the culture-positive ratio of M.TB and NTM between the two method groups (p < 0.05). Compared with that of the NALC-NaOH method (8.04%), sputum treated with PU method (4.86%) had a significantly lower contamination rate (p < 0.05). In conclusion, our data indicate that, compared with the NALC-NaOH method, the PU method is a rapid and effective approach for mycobacterial culture when detecting active TB. However, its accurate mechanism has not been well addressed, and further investigation is still required.

Discordant results of Xpert MTB/Rif assay and BACTEC MGIT 960 liquid culture to detect Mycobacterium tuberculosis in community screening in Vietnam

BACKGROUND

Xpert MTB/Rif, a molecular test to detect tuberculosis (TB), has been proven to have high sensitivity and specificity when compared with liquid culture in clinical settings. However, little is known about its performance in community TB screening.

METHODS

In Vietnam, a national TB prevalence survey was conducted in 2017. Survey participants who screened positive by chest X-ray, cough symptoms and/or recent history of tuberculosis were requested to provide at least two sputum samples that were tested for Mycobacterium tuberculosis by Xpert MTB/Rif G4 (Xpert) and BACTEC MGIT960 culture (MGIT).

RESULTS

There were 4,649 eligible participants provided both samples for testing. Among them, 236 (5.1%) participants tested positive for TB by Xpert, 244 (5.3%) tested positive by MGIT and 317 tested positive by at least one test; 163 (51.4%) had discordant test results. Of the positive Xpert, 162 (68.6%) showed a low or very low bacterial load. In multivariate logistic regression comparing discordant with Xpert-MGIT concordant positive results, discordant Xpert-positive results occurred more often among participants who had low sputum bacterial load, male sex, a history of TB treatment, or night sweats. The associated factors were male sex, abnormal chest X-ray and having night sweats when the logistic model was against those with both Xpert and MGIT negative.

CONCLUSIONS

We found high rates of discordance in the performance of Xpert and MGIT for community-based TB case finding. In situations where the majority of TB cases are expected to have a low bacterial load, multiple diagnostic tests and/or multiple samples are required to reach sufficient sensitivity.

Determining the Prevalence of Rifampicin Resistant Tuberculosis in A Tertiary Care Centre of North India by using Rapid Culture Method and Gene Xpert

The objective of the present study is to find the prevalence of Mycobacterium tuberculosis from respiratory samples like sputum, BAL and pleural fluid, compare conventional LJ culture with rapid culture method i.e Mycobacterium growth indicator tube (MGIT) and to determine the pattern of drug resistance by automated methods i.e Gene Xpert. Respiratory samples were collected in sterile, wide-mouth, disposable, leak proof containers without any preservatives. Specimens were inoculated into MGIT for primary isolation of Mycobacteria. The specimen was processed according to the SOP manual provided by Becton Dickinson Company. The tubes were read for increasing fluorescence by MGIT reader. Reported results only when a MGIT tube was positive by the MGIT reader and smear made from the positive broth is also positive for AFB. For further identification, TBcID card test was put from MGIT positive tube and the result was given accordingly as mentioned in the procedure for TBcID kit insert. Polymerase chain reaction (PCR) was done in all 17 positive cases. The drug sensitivity test (CB-NAAT) was done at State Intermediate Reference Laboratory, Chandan Nagar, Dehradun, Uttrakhand as per RNTCP laboratory operational guidelines. In our study total number of samples received from the clinically suspected cases of pulmonary tuberculosis were 156, out of which 11% were positive and 89% were negative. The predominant age group involved was 51-60 years 24%, followed by 61-70 years 22%. In young children and adolescent age group very less number of samples were received i.e. 0-5%. Out of 17 positive samples, 94.11% (16/17) were detected as sensitive for Rifampicin and 5.89% (1/17) were resistant. On the statistical analysis of our data for MGIT, Positive Predictive Value (PPV) was 29% against Negative Predictive Value (NPV) of 100%. The specificity of MGIT was 92% against a sensitivity of 100%. Culture is still needed for species identification, confirmation and drug susceptibility testing. The diagnostic superiority of MGIT, both in terms of sensitivity and specificity has been proven better as compared to LJ in previous other studies and supported by our study as well. In our study, the diagnostic efficacy of MGIT culture was found to be superior as compared to the conventional LJ culture. The positivity rate was 10.89% (17/156) in MGIT & 3.2% (5/156) in LJ culture.

Time to Detection of Growth for Mycobacterium tuberculosis in a Low Incidence Area

Background

Diagnosis of Mycobacterium tuberculosis (MTB) infection can be confirmed by Xpert assays within hours. However, when sample size does not allow performing both culture and Xpert, or if Xpert is negative, then formal diagnosis of MTB relies on culture and time to detection of growth (TDG) becomes critical for clinical management.

Objectives

To determine TDG in Xpert negative samples, or in samples in which Xpert could not be performed, in a low-incidence area for MTB.

Methods

Retrospective analysis (2015-2020) of a database including all cultures for mycobacteria in a University Hospital covering approximately 500'000 inhabitants. Analysis was restricted to culture positive (C+) samples for MTB for which 1/Xpert was negative or could not be performed because of limited sample volume, and 2/collected from subjects treated less than 24 hours. TDG was analyzed according to microscopy, origin of sample (pulmonary or not) and presence of cavitation.

Results

Among 837 C+ samples for MTB, 236 samples (80% of respiratory origin) from 147 patients fulfilled study criteria; 78 samples (49 patients, 33%) were acid-fast bacilli (AFB) positive. Median (IQR) TDG was 25 (17; 40) days for all samples. TDG exceeded 28 days in 43% of samples and was significantly shorter in AFB+ vs AFB- samples, and samples from cavitary vs non cavitary or extra-thoracic disease.

Conclusions

In Xpert negative samples, or samples for which Xpert could not be performed, TDG exceeded 4 weeks in 43% of samples. AFB+ and samples from cavitary lung disease had a significantly shorter TDG.

New management approaches to tuberculosis in people living with HIV

PURPOSE OF REVIEW

People living with HIV (PLWH) are commonly coinfected with Mycobacterium tuberculosis, particularly in high-transmission resource-limited regions. Despite expanded access to antiretroviral therapy and tuberculosis (TB) treatment, TB remains the leading cause of death among PLWH. This review discusses recent advances in the management of TB in PLWH and examines emerging therapeutic approaches to improve outcomes of HIV-associated TB.

RECENT FINDINGS

Three recent key developments have transformed the management of HIV-associated TB. First, the scaling-up of rapid point-of-care urine-based tests for screening and diagnosis of TB in PLWH has facilitated early case detection and treatment. Second, increasing the availability of potent new and repurposed drugs to treat drug-resistant TB has generated optimism about the treatment and outcome of multidrug-resistant and extensively drug-resistant TB. Third, expanded access to the integrase inhibitor dolutegravir to treat HIV in resource-limited regions has simplified the management of TB/HIV coinfected patients and minimized serious adverse events.

SUMMARY

While it is unequivocal that substantial progress has been made in early detection and treatment of HIV-associated TB, significant therapeutic challenges persist. To optimize the management and outcomes of TB in HIV, therapeutic approaches that target the pathogen as well as enhance the host response should be explored.

Baseline Xpert MTB/RIF ct values predict sputum conversion during the intensive phase of anti-TB treatment in HIV infected patients in Kampala, Uganda: a retrospective study

Background

In resource-limited settings, sputum smear conversion is used to document treatment response. Many People living with HIV (PLHIV) are smear-negative at baseline. The Xpert MTB/RIF test can indirectly measure bacterial load through cycle threshold (ct) values. This study aimed to determine if baseline Xpert MTB/RIF could predict time to culture negativity in PLHIV with newly diagnosed TB.

Methods

A subset of 138 PLHIV from the ‘SOUTH’ study on outcomes related to TB and antiretroviral drug concentrations were included. Bacterial load was estimated by Mycobacterium Growth Indicator Tubes (MGIT) culture time-to-positivity (TTP) and Lowenstein Jensen (LJ) colony counts. Changes in TTP and colony counts were analyzed with Poisson Generalised Estimating Equations (GEE) and multilevel ordered logistic regression models, respectively, while time to culture negativity analysed with Cox proportional hazard models. ROC curves were used to explore the accuracy of the ct value in predicting culture negativity.

Results

A total of 81 patients (58.7%) were males, median age 34 (IQR 29  – 40) years, median CD4 cell count of 180 (IQR 68  – 345) cells/μL and 77.5% were ART naive. The median baseline ct value was 25.1 (IQR 21.0  – 30.1). A unit Increase in the ct value was associated with a 5% (IRR = 1.05 95% CI 1.04  – 1.06) and 3% (IRR = 1.03 95% CI 1.03  – 1.04) increase in TTP at week 2 and 4 respectively. With LJ culture, a patient’s colony grade was reduced by 0.86 times (0R = 0.86 95% CI 0.74  – 0.97) at week 2 and 0.84 times (OR = 0.84 95% CI 0.79  – 0.95 P = 0.002) at week 4 for every unit increase in the baseline ct value. There was a 3% higher likelihood of earlier conversion to negativity for every unit increase in the ct value. A ct cut point ≥28 best predicted culture negativity at week 4 with a sensitivity of 91. 7% & specificity 53.7% while a cut point ≥23 best predicted culture negativity at week 8.

Conclusion

Baseline Xpert MTB/RIF ct values predict sputum conversion in PLHIV on anti-TB treatment. Surrogate biomarkers for sputum conversion in PLHIV are still a research priority.

Application value of tissue tuberculosis antigen combined with Xpert MTB/RIF detection in differential diagnoses of intestinal tuberculosis and Crohn's disease

Background

The purpose of this study was to examine the value of Xpert MTB/RIF assay and detection of additional Mycobacterium tuberculosis complex (MTBC) species antigens from intestinal tissue samples in differentiating intestinal tuberculosis (ITB) from Crohn’s disease (CD).

Methods

Several clinical specimens of intestinal tissue obtained by either endoscopic biopsy or surgical excision were used for mycobacteriologic solid cultures,Xpert MTB/RIF assays, immunohistochemistry, and histological examinations. Four antigens (38KDa, ESAT-6, MPT64, and Ag85 complex) of MTBC in the intestinal tissue were detected by immunohistochemical analysis.

Results

The study included 42 patients with ITB and 46 with CD. Perianal lesions and longitudinal ulcers were more common in patients with CD, while caseating granuloma and annular ulcers were more common in patients with ITB. The positive rate of MTBC detected by Xpert MTB/RIF in intestinal tissues of patients with ITB was 33.33%, which was significantly higher than that in patients with CD and that detected using acid-fast staining smears. It was also higher than that detected by tissue MTBC culture, but the difference was not statistically significant. The positive MPT64 expression rate in patients with ITB was 40.48%, which was significantly higher than that observed in patients with CD. The sensitivity of parallelly combined detection of tuberculosis protein MPT64 and Xpert MTB/RIF in diagnosing ITB was 50.0%.

Conclusions

The detection of Xpert MTB/RIF in intestinal tissue is a rapid and useful method for establishing an early diagnosis of ITB. The detection of MTBC using Xpert MTB/RIF and MPT64 antigen in intestinal tissues has a definitive value in the differential diagnosis ofITB and CD. The combination of these two methods can improve the detection sensitivity.

New Developments and Insights in the Improvement of Mycobacterium tuberculosis Vaccines and Diagnostics Within the End TB Strategy

PURPOSE OF REVIEW

The alignment of sustainable development goals (SDGs) with the End Tuberculosis (TB) strategy provides an integrated roadmap to implement key approaches towards TB elimination. This review summarizes current social challenges for TB control, and yet, recent developments in TB diagnosis and vaccines in the context of the End TB strategy and SDGs to transform global health.

RECENT FINDINGS

Advances in non-sputum based TB biomarkers and whole genome sequencing technologies could revolutionize TB diagnostics. Moreover, synergistic novel technologies such as mRNA vaccination, nanovaccines and promising TB vaccine models are key promising developments for TB prevention and control.

SUMMARY

The End TB strategy depends on novel developments in point-of-care TB diagnostics and effective vaccines. However, despite outstanding technological developments in these fields, TB elimination will be unlikely achieved if TB social determinants are not fully addressed. Indeed, the End TB strategy and SDGs emphasize the importance of implementing sustainable universal health coverage and social protection.

Mycobactericidal Effects of Different Regimens Measured by Molecular Bacterial Load Assay among People Treated for Multidrug-Resistant Tuberculosis in Tanzania

Rifampin or multidrug-resistant tuberculosis (RR/MDR-TB) treatment has largely transitioned to regimens free of the injectable aminoglycoside component, despite the drug class’ purported bactericidal activity early in treatment. We tested whether Mycobacterium tuberculosis

Rifampin or multidrug-resistant tuberculosis (RR/MDR-TB) treatment has largely transitioned to regimens free of the injectable aminoglycoside component, despite the drug class’ purported bactericidal activity early in treatment. We tested whether Mycobacterium tuberculosis killing rates measured by tuberculosis molecular bacterial load assay (TB-MBLA) in sputa correlate with composition of the RR/MDR-TB regimen. Serial sputa were collected from patients with RR/MDR- and drug-sensitive TB at days 0, 3, 7, and 14, and then monthly for 4 months of anti-TB treatment. TB-MBLA was used to quantify viable M. tuberculosis 16S rRNA in sputum for estimation of colony forming units per ml (eCFU/ml). M. tuberculosis killing rates were compared among regimens using nonlinear-mixed-effects modeling of repeated measures. Thirty-seven patients produced 296 serial sputa and received treatment as follows: 13 patients received an injectable bedaquiline-free reference regimen, 9 received an injectable bedaquiline-containing regimen, 8 received an all-oral bedaquiline-based regimen, and 7 patients were treated for drug-sensitive TB with conventional rifampin/isoniazid/pyrazinamide/ethambutol (RHZE). Compared to the adjusted M. tuberculosis killing of −0.17 (95% confidence interval [CI] −0.23 to −0.12) for the injectable bedaquiline-free reference regimen, the killing rates were −0.62 (95% CI −1.05 to −0.20) log₁₀ eCFU/ml for the injectable bedaquiline-containing regimen (P = 0.019), −0.35 (95% CI −0.65 to −0.13) log₁₀ eCFU/ml for the all-oral bedaquiline-based regimen (P = 0.054), and −0.29 (95% CI −0.78 to +0.22) log₁₀ eCFU/ml for the RHZE regimen (P = 0.332). Thus, M. tuberculosis killing rates from sputa were higher among patients who received bedaquiline but were further improved with the addition of an injectable aminoglycoside.

Evaluation of underweight status may improve identification of the highest-risk patients during outpatient evaluation for pulmonary tuberculosis

BACKGROUND

When evaluating symptomatic patients for tuberculosis (TB) without access to same-day diagnostic test results, clinicians often make empiric decisions about starting treatment. The number of TB symptoms and/or underweight status could help identify patients at highest risk for a positive result. We sought to evaluate the usefulness of BMI assessment and a count of characteristic TB symptoms for identifying patients at highest risk for TB.

METHODS

We enrolled adult patients receiving pulmonary TB diagnoses and a representative sample with negative TB evaluations at four outpatient health facilities in Kampala, Uganda. We asked patients about symptoms of chronic cough, night sweats, chest pain, fever, hemoptysis, or weight loss; measured height and weight; and collected sputum for mycobacterial culture. We evaluated the diagnostic accuracy (for culture-positive TB) of two simple scoring systems: (a) number of TB symptoms, and (b) number of TB symptoms plus one or more additional points for underweight status (body mass index [BMI] ≤ 18.5 kg/m2).

RESULTS

We included 121 patients with culture-positive TB and 370 patients with negative culture results (44 of whom had been recommended for TB treatment by evaluating clinicians). Of the six symptoms assessed, the median number of symptoms that patients reported was two (interquartile range [IQR]: 1, 3). The median BMI was 20.9 kg/m2 (IQR: 18.6, 24.0), and 118 (24%) patients were underweight. Counting the number of symptoms provided an area under the Receiver Operating Characteristic curve (c-statistic) of 0.77 (95% confidence interval, CI: 0.72, 0.81) for identifying culture-positive TB; adding two points for underweight status increased the c-statistic to 0.81 (95%CI: 0.76, 0.85). A cutoff of ≥3 symptoms had sensitivity and specificity of 65% and 74%, whereas a score of ≥4 on the combined score (≥2 symptoms if underweight, ≥4 symptoms if not underweight) gave higher sensitivity and specificity of 69% and 81% respectively. A sensitivity analysis defining TB by Xpert MTB/RIF status produced similar results.

CONCLUSION

A count of patients' TB symptoms may be useful in clinical decision-making about TB diagnosis. Consideration of underweight status adds additional diagnostic value.

Microscopic Observation Drug Susceptibility (MODS) Assay: A Convenient Method for Determining Antibiogram of Clinical Isolates of Mycobacterium tuberculosis in Ghana

(1) Background: Present methods for drug susceptibility tests (DST) rely on culture methods that are sophisticated and relatively faster, or a slow and cheaper option. These methods frustrate disease control; therefore, there is a need for methods that incorporate key functions of microscopy and culture, with reduced cost burden and sophistry. Thus, the purpose of this study was to identify which, among the most commonly used (in Ghana) methods, can conveniently be used at health centers located in rural areas for effective DST determination of Mycobacterium tuberculosis (MTB). (2) Methods: Mycobacterium tuberculosis isolates were tested for their susceptibility to streptomycin, isoniazid, rifampicin, ethambutol (SIRE), and pyrazinamide by microscopic observation drug susceptibility (MODS) and BACTEC MGIT 960 methods. Evaluations were based on shorter turnaround periods, rapidity, ease of use, cost, etc. A comparative analysis was statistically expressed as kappa values. (3) Results: Endpoints for drug susceptibilities by MODS averaged 13 days (7–32), whilst that for BACTEC MGIT 960 was 10 days with a further 12 days to detect resistance. Therefore, a turnaround period of 22 days was needed for DST by BACTEC MGIT 960, compared to 13 days for MODS. There were differences in correlation levels between the two methods, as determined by their kappa values. (4) Conclusion: The MODS assay was found to be less costly, more user-friendly, and still able to be conveniently used at health centers located in rural areas known to be endemic for TB, particularly in Ghana.

Diagnostic accuracy of the Xpert MTB/RIF assay for bone and joint tuberculosis: A meta-analysis

Background

This study aimed to evaluate the accuracy of the Xpert MTB/RIF assay for the diagnosis of bone and joint tuberculosis.

Methods

We searched databases from their inception to May 7, 2019 for published articles and reviewed them to assess the accuracy of Xpert MTB/RIF with respect to a composite reference standard (CRS) and mycobacterial culture. Meta-analyses were performed using a bivariate random-effects model, and the sources of heterogeneity were assessed via subgroup analysis and meta-regression.

Results

Nineteen independent (9 prospective, 5 retrospective, and 5 case-control) studies that compared Xpert MTB/RIF with the CRS and 14 (6 prospective, 7 retrospective, and 1 case-control) studies that compared it with culture were included. The pooled sensitivity and specificity of Xpert MTB/RIF were 81% (95% confidence interval [CI], 77–84) and 99% (95% CI, 97–100) compared to the CRS, respectively, and 96% (95% CI, 90–98) and 85% (95% CI, 57–96) compared to culture, respectively. The pooled sensitivity and specificity using pus samples vs. the CRS were 82% (95% CI, 76–86) and 99% (95% CI, 95–100), respectively. The proportions obtained while working with tissue samples vs. the CRS were 84% (95% CI, 76–90) and 98% (95% CI, 94–99), respectively. There was no significant difference in diagnostic accuracy among the types of specimens.

Conclusions

Xpert MTB/RIF demonstrates good diagnostic accuracy for bone and joint tuberculosis, the results of which are not related to the type of specimen.

Identification and Characterization of Genetic Determinants of Isoniazid and Rifampicin Resistance in Mycobacterium tuberculosis in Southern India

Drug-resistant tuberculosis (TB), one of the leading causes of death worldwide, arises mainly from spontaneous mutations in the genome of Mycobacterium tuberculosis. There is an urgent need to understand the mechanisms by which the mutations confer resistance in order to identify new drug targets and to design new drugs. Previous studies have reported numerous mutations that confer resistance to anti-TB drugs, but there has been little systematic analysis to understand their genetic background and the potential impacts on the drug target stability and/or interactions. Here, we report the analysis of whole-genome sequence data for 98 clinical M. tuberculosis isolates from a city in southern India. The collection was screened for phenotypic resistance and sequenced to mine the genetic mutations conferring resistance to isoniazid and rifampicin. The most frequent mutation among isoniazid and rifampicin isolates was S315T in katG and S450L in rpoB respectively. The impacts of mutations on protein stability, protein-protein interactions and protein-ligand interactions were analysed using both statistical and machine-learning approaches. Drug-resistant mutations were predicted not only to target active sites in an orthosteric manner, but also to act through allosteric mechanisms arising from distant sites, sometimes at the protein-protein interface.

Evaluation of a manual identification system for detection of Mycobacterium tuberculosis in a primary tuberculosis laboratory in China

OBJECTIVE

To compare the diagnostic performance of the manual BACTEC™ Mycobacteria Growth Indicator Tube (MGIT™) system (M-MGIT) with the automated BACTEC™ MGIT™ 960 system (A-MGIT) and Löwenstein-Jensen (L-J) culture method in detecting mycobacteria in sputum specimens from patients with suspected pulmonary tuberculosis (TB).

METHODS

For this cross-sectional study, sputum samples were taken from patients aged ≥18 years attending a TB clinic in Beijing, China between July 2015 and October 2016. Processed sputum samples were inoculated into the MGIT systems and L-J medium for up to 6 and 8 weeks, respectively.

RESULTS

The M-MGIT and A-MGIT methods detected significantly more Mycobacterium tuberculosis complex (MTC) isolates than L-J culture from the 565 sputum samples (39%, 40% and 32%, respectively). Using a positive result from any of the three culture systems as reference, the sensitivity of M-MGIT, A-MGIT and L-J methods were 92%, 94%, and 74%, respectively. The time-to-detection of mycobacteria was 12.9±4.2 days for M-MGIT, 11.8±5.2 days for A-MGIT and 24.2±8.7 days for L-J.

CONCLUSIONS

M-MGIT has a similar diagnostic performance to A-MGIT, and is a fast and reliable alternative to conventional culture methods in the diagnosis of pulmonary TB in a developing country.