Comparison of direct versus concentrated smear microscopy in detection of pulmonary tuberculosis

Clinical and Imaging Characteristics of Smear Negative Pulmonary Tuberculosis Patients: A Comparative Study

Background

Prevalence surveys in Ethiopia indicate smear negative pulmonary tuberculosis (SNPTB) taking the major share of the overall TB burden. It has also been a diagnostic dilemma worldwide leading to diagnostic delays and difficulty in monitoring treatment outcomes. This study determines and compares the clinical and imaging findings in SNPTB and smear positive PTB (SPPTB). Methodology. A case-control study was conducted on 313 PTB (173 SNPTB) patients. Data and sputum samples were collected from consented patients. Smear microscopy, GeneXpert, and culture analyses were performed on sputum samples. Data were analyzed using Stata version 17; a P value < 0.05 was considered statistically significant.

Results

Of the 173 SNPTB patients, 42% were culture positive with discordances between test results reported by health facilities and Armauer Hansen Research Institute laboratory using concentrated smear microscopy. A previous history of TB and fewer cavitary lesions were significantly associated with SNPTB.

Conclusions

Though overall clinical presentations of SNPTB patients resemble those seen in SPPTB patients, a prior history of TB was strongly associated with SNPTB. Subject to further investigations, the relatively higher discrepancies seen in TB diagnoses reflect the posed diagnostic challenges in SNPTB patients, as a higher proportion of these patients are also seen in Ethiopia.

Use of light-emitting diode fluorescence microscopy to detect acid-fast bacilli in sputum as proficient alternative tool in the diagnosis of pulmonary tuberculosis in countries with limited resource settings

Background

Despite recent advances in the development of more sensitive technologies for the diagnosis of tuberculosis (TB), in resource-limited settings, the diagnosis continues to rely on sputum smear microscopy. This is because smear microscopy is simple, cost-efficient and the most accessible tool for the diagnosis of TB. Our study evaluated the performance of light-emitting diode fluorescence microscopy (LED-FM) using auramine/rhodamine (auramine) and the fluorescein di-acetate (FDA) vital stain in the diagnostic of pulmonary TB in Bamako, Mali.

Methods

Sputum smear microscopy was conducted using the FDA and auramine/rhodamine staining procedures on fresh samples using LED-FM to evaluate the Mycobacterium TB (MTB) metabolic activity and to predict contagiousness. Mycobacterial culture assay was utilized as a gold standard method.

Results

Out of 1401 TB suspected patients, 1354 (96.65%) were retrieved from database, which were MTB complex culture positive, and 47 (3.40%) were culture negative (no mycobacterial growth observed). Out of the 1354 included patients, 1343 (95.86%), were acid-fast bacillus (AFB) positive after direct FDA staining, 1352 (96.50%) AFB positive after direct Auramine, and 1354 (96.65%) AFB positive with indirect auramine after digestion and centrifugation. Overall, the FDA staining method has a sensitivity of 98.82%, while the sensitivity of Auramine with direct observation was 99.48%, and 99.56% with the indirect examination.

Conclusion

This study showed that, using fresh sputum both auramine/rhodamine and FDA are highly sensitive methods in diagnosing pulmonary TB and could be easily used in countries with limited resource settings.

Diagnostic Yield of Xpert MTB/RIF Assay Using Bronchoalveolar Lavage Fluid in Detecting Mycobacterium tuberculosis among the Sputum-Scarce Suspected Pulmonary TB Patients

Tuberculosis (TB) remains one of the leading causes of death worldwide and is caused by the single infectious agent Mycobacterium tuberculosis (Mtb). Although sputum is the most common specimen for pulmonary TB detection, some other respiratory specimens, such as bronchoalveolar lavage (BAL) fluid, gastric lavage (GL), and induced sputum (IS), are also collected from patients who are unable to deliver sputum. In this study, we aimed to evaluate the diagnostic performances of different test methods for TB diagnosis using BAL fluid specimens from sputum-scarce pulmonary TB patients. In this current study, a total of 210 BAL fluid specimens were collected and subjected to culture on Lowenstein–Jensen (L-J) medium, using an N-acetyl-L-cysteine-Sodium Hydroxide decontamination and digestion method, Xpert MTB/RIF (Xpert, Cepheid, Sunnyvale, CA, USA) assay, and acid-fast bacilli (AFB) microscopy with a Ziehl–Neelsen staining method for the detection of pulmonary TB. The sensitivity and specificity of these methods were then analyzed against the composite reference standard (CRS). Additionally, the receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of these assays. Among the 210 specimens, 39 (18.6%), 27 (12.8%), and 12 (5.7%) were found positive with Xpert assay, culture, and AFB microscopy, respectively. Considering the CRS, 42 (20%) were positive as the final diagnosis. The Xpert assay had a significantly higher sensitivity (92.9%, 95% CI: 80.5–98.5) compared to culture (64.3%, 95% CI: 48.0–78.4) and AFB microscopy (28.6%, 95% CI: 15.7–44.6) against the CRS. Additionally, the area under the ROC curve (AUC) for the Xpert assay, culture, and AFB microscopy accounted for 0.964, 0.821, and 0.655, respectively, when using CRS as the reference. In conclusion, our study findings demonstrated that the Xpert assay conferred a considerable diagnostic potential compared to other conventional methods for the diagnosis of pulmonary TB from BAL fluid specimens.

Concentrated specimen smear microscopy utilising a polymer membrane sandwich filtration vessel for the detection of acid-fast bacilli in health facilities in Sabah, East Malaysia

A simple, ready-to-use concentrated specimen smear microscopy method employing a nanometer silicon polyvinylidene fluoride (PVDF) polymer membrane sandwich filtration vessel to concentrate acid-fast bacilli (AFB) in samples (SFV-CSSM, Hunan-Tech New Medical System Co. Ltd. China) was compared with direct sputum smear microscopy (DSSM) to determine its performance using culture on modified Ogawa agar as reference. The results for 4114 clinical samples collected from health facilities in Sabah were interpreted with reference to culture results, sample collection-transportation conditions and clinical data including responses to anti-TB drug treatment. The SFV-CSSM showed higher sensitivity than DSSM (79.4% versus 60.5%) and less background interference. Its ability to detect low levels of AFB at an affordable cost makes it an excellent tool for the screening of pauci-bacillary samples as well as for active case finding in TB control programs.

Xpert MTB/RIF Ultra assay for the detection of Mycobacterium tuberculosis in people with negative conventional Xpert MTB/RIF but chest imaging suggestive of tuberculosis in Dhaka, Bangladesh: Xpert Ultra for M. tuberculosis detection in Xpert-negative PTB presumptives

BACKGROUND

World Health Organization is considering substitution of Xpert MTB/RIF (Xpert) by Xpert MTB/RIF Ultra (Ultra) for tuberculosis (TB) diagnosis, but supportive evidence is scarce, particularly among people more likely to have paucibacillary pulmonary TB (PTB).

METHODS

During January-July 2018, PTB presumptives visiting TB Screening and Treatment Centres of Dhaka for routine chest X-ray (CXR) and conventional Xpert were enrolled. Sputum specimens were additionally tested with microscopy, culture and Ultra. Specimens with "Trace call" by Ultra (Ultra-trace) were retested. Yield and diagnostic accuracy using various approaches to Ultra-trace and concordance of Ultra with bacteriological-positive PTB were assessed.

RESULTS

1,083 participants (104 'Xpert-positive'; 979 'Xpert-negative and CXR-suggestive') were enrolled. All Xpert-positives and 900 (92%) Xpert-negatives displayed concordance with Ultra. Seventy-nine (8.1%) Xpert-negative specimens tested positive with Ultra, of which 37 (46.8%) were categorically positives and 42 (53.2%) were Ultra-trace. Sixteen of 42 were retested, of whom eight (50.1%) Ultra-trace turned categorically positive, leading to 45 (4.6%) additionally detected by Ultra. Ultra sensitivity and specificity was 93.9% and 94.6%, and it additionally detected 5.4% more TB patients with concordance 94.6% (kappa, ꓗ=0.78) compared to any bacteriologically positive specimen (microscopy, culture or Xpert).

CONCLUSION

Ultra exhibited improved detection and accuracy among Xpert-negatives in a cohort with a high likelihood of PTB.

Costs and cost-effectiveness of Gene Xpert compared to smear microscopy for the diagnosis of pulmonary tuberculosis using real-world data from Arsi zone, Ethiopia

Background

Early diagnosis and treatment are one of the key strategies of tuberculosis control globally, and there are strong efforts in detecting and treating tuberculosis cases in Ethiopia. Smear microscopy examination has been a routine diagnostic test for pulmonary tuberculosis diagnosis in resource-constrained settings for decades. Recently, many countries, including Ethiopia, are scaling up the use of Gene Xpert without the evaluation of the cost and cost-effectiveness implications of this strategy. Therefore, this study evaluated the cost and cost-effectiveness of Gene Xpert (MTB/RIF) and smear microscopy tests to diagnosis tuberculosis patients in Ethiopia.

Methods

We compared the costs and cost-effectiveness of tuberculosis diagnosis using smear microscopy and Gene Xpert among 1332 patients per intervention in the Arsi zone. We applied combinations of top-down and bottom-up costing approaches. The costs were estimated from the health providers’ perspective within one year (2017–2018). We employed “cases detected” as an effectiveness measure, and the incremental cost-effectiveness ratio was calculated by dividing the changes in cost and change in effectiveness. All costs and incremental cost-effectiveness ratio were reported in 2018 US$.

Results

The unit cost per test for Gene Xpert was $12.9 whereas it is $3.1 for AFB smear microscopy testing. The cost per TB case detected was $77.9 for Gene Xpert while it was $55.8 for the smear microscopy method. The cartridge kit cost accounted for 42% of the overall Gene Xpert’s costs and the cost of the reagents and consumables accounted for 41.3% ($1.3) of the unit cost for the smear microscopy method. The ICER for the Gene Xpert strategy was $20.0 per tuberculosis case detected.

Conclusion

Using Gene Xpert as a routine test instead of standard care (smear microscopy) can be potentially cost-effective. In the cost scenario analysis, the price of the cartridge, the number of tests performed per day, and the life span of the capital equipment were the drivers of the unit cost of the Gene Xpert method. Therefore, Gene Xpert can be a part of the routine TB diagnostic testing strategy in Ethiopia.

Genetic diversity and characterization of M. tuberculosis isolates causing extrapulmonary tuberculosis in Bangladesh

Tuberculosis (TB) remains one of the leading causes of death and Bangladesh ranks 7th among the highest TB burden countries. Though molecular epidemiological data for pulmonary TB (PTB) have previously been described in Bangladesh, data on the molecular characterization and clinical association with different lineages among extrapulmonary TB (EPTB) is lacking. The aim of the study was to investigate the molecular characterization and lineage distribution of M. tuberculosis isolates obtained from patients with EPTB in Bangladesh. Between November 2015 and March 2017, a total of 1,340 EPTB specimens including lymph node, pus, tissue, ascitic fluid, cerebrospinal fluid, pleural fluid, abscess wall, urine etc. were collected from four tertiary care hospitals in Dhaka city, Bangladesh. Among the specimens, 141 were found positive on solid culture. Molecular characterization of the 141 isolates was done by deletion analysis, spoligotyping and Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem Repeats (MIRU-VNTR) analysis. Among the 141 isolates, 80 (56.7%) were found as 'modern' and the remaining 61 (43.3%) were 'ancestral' type. Spoligotyping results revealed 91 distinct patterns of which 74 isolates were unique and the remaining 67 were divided into 17 distinct clusters. East African- Indian (EAI) lineage was the most predominant, comprising 26 (18.4%) isolates, followed by the Beijing lineage (14.2%). 15-loci MIRU-VNTR analysis revealed that 132 isolates (93.5%) had unique patterns, whereas only 9 (6.5%) isolates were grouped into 4 distinct clusters. In conclusion, the study findings provide a first insight into genetic diversity of EPTB isolates in Bangladesh. The present study demonstrated that 'modern' strains were more prevalent among the EPTB cases, while EAI lineages were predominantly circulating in this region.

Integrated nucleic acid testing system to enable TB diagnosis in peripheral settings

To facilitate treatment and limit transmission of tuberculosis (TB), new methods are needed to enable rapid and affordable diagnosis of the disease in high-burden low-resource settings. We have developed a prototype integrated nucleic acid testing device to detect Mycobacterium tuberculosis (M.tb) in sputum. The device consists of a disposable cartridge and compact, inexpensive instrument that automates pathogen lysis, nucleic acid extraction, isothermal DNA amplification and lateral flow detection. A liquefied and disinfected sputum sample is manually injected into the cartridge, and all other steps are automated, with a result provided in <1.5 h. Cell disruption and DNA extraction is executed within a four-port active valve containing a miniature bead blender (based on PureLyse® technology, Claremont BioSolutions LLC). The DNA-containing eluate is combined with dry master-mix reagents and target DNA is isothermally amplified. Amplified master-mix is then pumped into a lateral flow strip chamber for detection. The entire process is performed in a single-use closed-system cartridge to prevent amplicon carryover. For testing of M.tb-spiked sputum the system provided a limit of detection of 5 × 103 colony forming units (CFU) per mL. None of the negative sputum-only controls yielded a false-positive result. Testing of 45 clinical sputum specimens from TB cases and controls relative to a validated manual qPCR-based comparator method revealed a preliminary sensitivity of 90% and specificity of 96%. With further development, the herein described integrated nucleic acid testing device can enable TB diagnosis and treatment initiation in the same clinical encounter in near-patient low-resource settings of high TB burden countries.

Distribution and Frequency of rpoB Mutations Detected by Xpert MTB/RIF Assay Among Beijing and Non-Beijing Rifampicin Resistant Mycobacterium tuberculosis Isolates in Bangladesh

Background

Rifampicin resistance (RR) is a key indicator of multidrug-resistant tuberculosis (MDR-TB) and 95% of the RR is associated with the mutation in the 81-bp rifampicin resistance determining region (RRDR) of the rpoB gene of Mycobacterium tuberculosis complex (MTBC). The Xpert MTB/RIF (Xpert) assay uses five overlapping molecular beacon probes (A-E) complementary to RRDR region that detect MTBC and mutations associated with RR. The objective of the study was to investigate the distribution and frequency of mutations detected by Xpert assay among Beijing and non-Beijing RR-TB isolates.

Methods

A total of 205 randomly selected RR-TB specimens detected by Xpert assay were included in this study. A portion of specimens was further subjected to culture, MTBDRplus test and the positive culture isolates were genotyped by spoligotyping.

Results

We found that the most frequent mutation occurred at probe E (S531L) binding region in both Beijing and non-Beijing isolates (61.9% and 66.9%, respectively). The Beijing family had higher mutation rates than non-Beijing (19.0% vs 12.4%) at probe B (D516V) while the non-Beijing family had higher mutations at probe D (H526D or H526Y) than the Beijing (13.2% vs 10.7%) family. Mutations at probes Aand C were less common in both Beijing and non-Beijing isolates. There was no significant difference (P=0.36) in the occurrence of mutations at different probes between Beijing and non-Beijing isolates.

Conclusions

The study results revealed that the most frequent mutation occurs in the region of probe E and the least common mutations at probe A and C among both Beijing and non-Beijing RR-TB cases. This first insight into the probe mutation variation and frequencies among the RR-TB cases in Bangladesh forms the baseline information for further investigation.

Multicenter evaluation of membrane-based smear microscopy for detecting acid-fast bacilli in China

OBJECTIVE

To assess the feasibility and reliability of using membrane-based smear microscopy at peripheral laboratories in China.

METHODS

The clinical case control study was conducted in five tuberculosis (TB) dispensaries from September 2014 to May 2016. The membrane-based microscopy and direct smear microscopy were performed to compare the sensitivity, specificity, and the examination time for both methods was also analyzed.

RESULTS

A total of 5359 TB suspects were consecutively enrolled from 5 TB dispensaries, and 9915 specimens were finally analyzed. The sensitivity for membrane-based microscopy and direct smear microscopy was 76.9% (95% CI, 75.4-78.4) and 53.8% (95% CI, 52.1-55.6) respectively, and the specificity was 96.8% (95% CI, 96.4-97.2) and 99.2% (95% CI, 99.0-99.4) respectively. The sensitivity and specificity were both significantly different (P<0.001) between the two methods. The examination time for membrane-based smear microscopy (209.1±112.0 seconds) was significantly shorter than that for direct smear microscopy (253.1±79.4 seconds) (P<0.05).

CONCLUSIONS

Membrane-based smear microscopy showed higher sensitivity and a shorter examination time in comparison with direct smear microscopy and it could be used at peripheral laboratories in China.

Evaluation of Xpert MTB/RIF assay for detection of Mycobacterium tuberculosis in stool samples of adults with pulmonary tuberculosis

BACKGROUND

The Xpert MTB/RIF (Xpert) assay technology allows rapid and sensitive diagnosis of pulmonary tuberculosis (PTB) from sputum specimens. However, diagnosis of PTB is difficult for patients who cannot produce sputum. The objective of this study was to investigate the use of Xpert assay for successful detection of PTB using stool samples from adult subjects.

METHODS

Both stool and sputum samples from known smear and Xpert positive PTB patients were collected from a TB hospital in Dhaka. Stool samples were collected from healthy individuals without TB symptoms from a slum area of Dhaka. Stool and sputum samples were decontaminated and concentrated using NALC-NaOH-Na-citrate solution and the resultant sediment was used for Xpert, acid-fast bacilli (AFB) microscopy and culture.

RESULTS

A total of 102 stool samples were collected from PTB patients and another 50 stool samples from healthy individuals without TB. The sensitivity of the Xpert assay for detection of M. tuberculosis in stool samples of PTB patients was 90.2% (95% CI, 82.9-95.0). All 50 stool samples from healthy individuals were negative by the assay (Specificity 100%; 95% CI, 92.9-100). Compared with the sputum culture positive results the sensitivity of the stool Xpert assay was 94.8% (95% CI, 88.5-97.8). Moreover, stool Xpert demonstrated full concordant results with the sputum culture for detection of rifampicin susceptibility. The cycle threshold values of rpoB probes obtained from Xpert assay correlated significantly with the bacilli load in the corresponding stool (Spearman correlation = -0.40, P < 0.01) and sputum (Spearman correlation = -0.77, P < 0.01) samples as determined by microscopy.

CONCLUSIONS

Stool Xpert can be applied as a potential alternative of sputum testing for detection of M. tuberculosis and accurate determination of RIF susceptibility in adult PTB patients. The assay would be beneficial for rapid diagnosis of PTB for those adult patients who cannot expectorate sputum.

Molecular characterization and drug susceptibility profile of Mycobacterium tuberculosis isolates from Northeast Bangladesh

Tuberculosis (TB) remains a major public health problem worldwide including in Bangladesh. Molecular epidemiological tools provide genotyping profiles of Mycobacterium tuberculosis (M. tuberculosis) strains that can give insight into the transmission of TB in a specific region. The objective of the study was to identify the genetic diversity and drug susceptibility profile of M. tuberculosis strains circulating in the northeast Bangladesh. A total of 244 smear-positive sputum specimens were collected from two referral hospitals in Mymensingh and Netrakona districts. The isolated strains were genotyped by deletion analysis, spoligotyping, and MIRU-VNTR typing. We also analyzed the distributions of drug susceptibility pattern and demographic data among different genotypes. All isolates were identified as M. tuberculosis and among them 167 strains (68.44%) were 'ancestral' and the remaining 77 (31.56%) were 'modern' type. Spoligotyping analysis yielded 119 distinct patterns, among them, 86 isolates had unique patterns and the remaining 158 were grouped into 33 distinct clusters containing 2 to 18 isolates. The predominant spoligotypes belong to the EAI lineage strains, comprising 66 (27.04%) isolates followed by Beijing (7.38%), T1 (6.15%), CAS1-Delhi (5.33), LAM9 (3.28%), MANU-2 and X2. MIRU-VNTR analysis revealed 167 isolates (68%) had unique patterns, whereas 77 (32%) were grouped into 26 clusters and the rate of recent transmission was 20.9%, suggesting that the majority of TB cases in this region are caused by the reactivation of previous TB infections rather than recent transmission. About 136 (55.7%) isolates were sensitive to four anti-TB drugs, 69 (28.3%) were resistant to one or more (except rifampicin and isoniazid combination) drugs and 39 (15.9%) were MDR. In conclusion, our study provides a first insight into molecular characterization and drug resistance profile of M. tuberculosis strains in northeast Bangladesh which will ultimately contribute to the national TB control program.

Pediatric tuberculosis detection using trained African giant pouched rats

BACKGROUND

Tuberculosis (TB) diagnosis in children is a challenge with up to 94% of children with TB treated empirically in TB high-burden countries. Therefore, new diagnostic tests are needed for TB diagnosis. We determined the performance of trained rats in the diagnosis of pediatric TB and whether they can improve detection rate compared to the standard of care.

METHODS

Presumptive TB patients in 24 TB clinics in Tanzania were tested. Samples indicated as TB-positive by rats underwent confirmation by concentrated smear microscopy. TB yield of bacteriologically confirmed pediatric TB patients (≤5 years) was compared with yield of standard of care.

RESULTS

Sputum samples from 55,148 presumptive TB patients were tested. Nine hundred eighty-two (1.8%) were the children between 1 and 5 years. Clinics detected 34 bacteriologically positive children, whereas rats detected additional 23 children yielding 57 bacteriologically TB-positive children. Rats increased pediatric TB detection by 67.6%. Among 1-14-year-old children, clinics detected 331 bacteriologically positive TB whereas rats found the additional 208 children with TB that were missed by clinics. Relative increase in TB case detection by rats decreased with the increase in age (P<0.0001).

CONCLUSION

Trained rats increase pediatric TB detection significantly and could help address the pediatric TB diagnosis challenges. Further determination of accuracy of rats involving other sample types is still needed.

Role of PCR method using IS6110 primer in detecting Mycobacterium tuberculosis among the clinically diagnosed childhood tuberculosis patients at an urban hospital in Dhaka, Bangladesh

OBJECTIVE

Better methods are needed for the accurate detection of child tuberculosis (TB). This study compared different laboratory tests and evaluated IS6110 PCR for the detection of Mycobacterium tuberculosis (MTB) among clinically diagnosed child TB patients.

METHODS

A total of 102 paediatric patients (<15 years old) with clinically diagnosed TB were enrolled in this study. The patients were admitted to the icddr,b hospital in Dhaka between 2003 and 2005. Sputum/gastric lavage samples were collected for smear microscopy, culture (solid/Lowenstein-Jensen medium and liquid/MGIT), and IS6110 PCR testing. The sensitivity, specificity, and positive and negative predictive values (PPV, NPV) of smear microscopy and PCR were compared to the two culture methods.

RESULTS

Three patients were positive on smear microscopy (2.9%). MTB was detected by conventional culture in 15.7% (16/102), liquid culture in 14% (14/100), and IS6110 PCR in 61.8% (63/102). PCR detected an additional 45 patients who were undetected with the three other tests. Compared to conventional and liquid culture, respectively, smear microscopy showed sensitivity of 18.8% and 21.4%, specificity of 100% individually, PPV of 100% individually, and NPV of 86.9% and 88.7%, whereas PCR had sensitivity of 87.5% and 92.9%, specificity of 43% individually, PPV of 22.2% and 21%, and NPV of 94.9% and 97.4%.

CONCLUSIONS

PCR can be useful compared to smear microscopy and culture methods and is applicable as a rapid screening test for child TB. A larger scale study is required to determine its diagnostic efficacy in improving the detection of child TB in the presence and absence of severe malnutrition.

Low cost automated whole smear microscopy screening system for detection of acid fast bacilli

Background

In countries with high tuberculosis (TB) burden, there is urgent need for rapid, large-scale screening to detect smear-positive patients. We developed a computer-aided whole smear screening system that focuses in real-time, captures images and provides diagnostic grading, for both bright-field and fluorescence microscopy for detection of acid-fast-bacilli (AFB) from respiratory specimens.

Objectives

To evaluate the performance of dual-mode screening system in AFB diagnostic algorithms on concentrated smears with auramine O (AO) staining, as well as direct smears with AO and Ziehl-Neelsen (ZN) staining, using mycobacterial culture results as gold standard.

Methods

Adult patient sputum samples requesting for M. tuberculosis cultures were divided into three batches for staining: direct AO-stained, direct ZN-stained and concentrated smears AO-stained. All slides were graded by an experienced microscopist, in parallel with the automated whole smear screening system. Sensitivity and specificity of a TB diagnostic algorithm in using the screening system alone, and in combination with a microscopist, were evaluated.

Results

Of 488 direct AO-stained smears, 228 were culture positive. These yielded a sensitivity of 81.6% and specificity of 74.2%. Of 334 direct smears with ZN staining, 142 were culture positive, which gave a sensitivity of 70.4% and specificity of 76.6%. Of 505 concentrated smears with AO staining, 250 were culture positive, giving a sensitivity of 86.4% and specificity of 71.0%. To further improve performance, machine grading was confirmed by manual smear grading when the number of AFBs detected fell within an uncertainty range. These combined results gave significant improvement in specificity (AO-direct:85.4%; ZN-direct:85.4%; AO-concentrated:92.5%) and slight improvement in sensitivity while requiring only limited manual workload.

Conclusion

Our system achieved high sensitivity without substantially compromising specificity when compared to culture results. Significant improvement in specificity was obtained when uncertain results were confirmed by manual smear grading. This approach had potential to substantially reduce workload of microscopists in high burden countries.

Evaluation of the Xpert® MTB/RIF assay and microscopy for the diagnosis of Mycobacterium tuberculosis in Namibia

BACKGROUND

Tuberculosis (TB) kills approximately two million people and infects around nine million worldwide annually. Its proper management, especially in resource-limited settings, has been hindered by the lack of rapid and easy-to-use diagnostic tests. Sputum smear microscopy remains the cheapest, readily available diagnostic method but it only identifies less than half of the patients with a HIV/TB co-infection because the bacilli would have disseminated from the lungs to other areas of the body. The fully automated Xpert® MTB/RIF assay is a promising innovation for diagnosing TB and detecting resistance to rifampicin. This study aimed to evaluate the use of Xpert® MTB/RIF assay and microscopy in the diagnosis of Mycobacterium tuberculosis in Namibia, by determining the disease's epidemiology and calculating the proportion of cases infected just with TB and those with a resistance to rifampicin among the total suspected cases of TB in the country.

METHODS

This retrospective study analysed TB cases that were diagnosed using both the Xpert® MTB/RIF assay and microscopy. Data were collected from patient records from the Meditech laboratory information system of the Namibia Institute of Pathology for the time period of July 2012-April 2013. Data from 13 regions were collected.

RESULTS

The total number of specimens collected from patients with symptoms of pulmonary TB was 1 842. Of these, 594 (32.20%) were found to be positive for MTB by Xpert® MTB/RIF assay, out of which 443 (24.05%) were also found to be positive by microscopy. The remainder was negative. The male patients were more resistant to rifampicin when compared to the female patients.

CONCLUSIONS

Tuberculosis is widely distributed throughout Namibia, with slightly more males infected than females. Most TB patients are also co-infected with HIV. Both microscopy and Xpert® MTB/RIF assay are crucial for the diagnosis of TB in the country. Screening diagnostic efforts should focus on the sexually active HIV positive male population who could be the source of more RIF-resistant TB than females to prevent its spread.

Active tuberculosis detection by pouched rats in 2014: More than 2,000 new patients found in two countries

Tuberculosis (TB) is a major problem in poor countries because sensitive diagnostic tools are unavailable. In 2014, our pouched rats evaluated sputum from 21,600 Tanzanians and 9,048 Mozambicans whose sputum had previously been evaluated by microscopy, the standard diagnostic for TB. Evaluation by the rats revealed 1,412 new patients with active TB in Tanzania and 645 new patients in Mozambique, increases of 39% and 53%, respectively, when compared to detections by microscopy alone. These results provide further support for the applied use of scent-detecting rats.

Two Multiplex Real-Time PCR Assays to Detect and Differentiate Acinetobacter baumannii and Non- baumannii Acinetobacter spp. Carrying blaNDM, blaOXA-23-Like, blaOXA-40-Like, blaOXA-51-Like, and blaOXA-58-Like Genes

Nosocomial infections caused by Acinetobacter spp. resistant to carbapenems are increasingly reported worldwide. Carbapenem-resistant Acinetobacter (CRA) is becoming a serious concern with increasing patient morbidity, mortality, and lengths of hospital stay. Therefore, the rapid detection of CRA is essential for epidemiological surveillance. Polymerase chain reaction (PCR) has been extensively used for the rapid identification of most pathogens. In this study, we have developed two multiplex real-time PCR assays to detect and differentiate A. baumannii and non-A. baumannii Acinetobacter spp, and common carbapenemase genes, including bla_NDM, bla_OXA-23-like, bla_OXA-40-like, bla_OXA-51-like, and bla_OXA-58-like. We demonstrate the potential utility of these assays for the direct detection of bla_NDM-, bla_OXA-23-like-, bla_OXA-40-like-, bla_OXA-51-like-, and bla_OXA-58-like-positive CRA in clinical specimens. Primers were specifically designed, and two multiplex real-time PCR assays were developed: multiplex real-time PCR assay1 for the detection of Acinetobacter baumannii 16S–23S rRNA internal transcribed spacer sequence, the Acinetobacter recA gene, and class-B-metalloenzyme-encoding gene bla_NDM; and multiplex real-time PCR assay2 to detect class-D-oxacillinase-encoding genes (bla_OXA-23-like, bla_OXA-40-like, bla_OXA-51-like,and bla_OXA-58-like). The assays were performed on an ABI Prism 7500 FAST Real-Time PCR System. CRA isolates were used to compare the assays with conventional PCR and sequencing. Known amounts of CRA cells were added to sputum and fecal specimens and used to test the multiplex real-time PCR assays. The results for target and nontarget amplification showed that the multiplex real-time PCR assays were specific, the limit of detection for each target was 10 copies per 20 μL reaction volume, the assays were linear over six log dilutions of the target genes (r² > 0.99), and the Ct values of the coefficients of variation for intra- and interassay reproducibility were less than 5%. The multiplex real-time PCR assays showed 100% concordance with conventional PCR when tested against 400 CRA isolates and their sensitivity for the target DNA in sputum and fecal specimens was 10² CFU/mL. Therefore, these novel multiplex real-time PCR assays allow the sensitive and specific characterization and differentiation of bla_NDM-, bla_OXA-23-like-, bla_OXA-40-like-, bla_OXA-51-like-, and bla_OXA-58-like-positive CRA, making them potential tools for the direct detection of CRA in clinical specimens and the surveillance of nosocomial infections.

Assessment of terbium (III) as a luminescent probe for the detection of tuberculosis biomarkers

A detection method for nicotinic acid, a specific metabolite marker of Mycobacterium tuberculosis present in cultures and patients' breath, is studied in complex solutions containing other metabolites and in biological media such as urine, saliva and breath condensate. The method is based on the analysis of the luminescence increase of Tb(3+) complexes in the presence of nicotinic acid due to the energy transfer from the excited ligand to the lanthanide ion. It is shown that other potential markers found in M. tuberculosis culture supernatant, such as methyl phenylacetate, p-methyl anisate, methyl nicotinate and 2-methoxy biphenyl, can interfere with nicotinic acid via a competitive absorption of the excitation photons. A new strategy to circumvent these interferences is proposed with an upstream trapping of volatile markers preceding the detection of nicotinic acid in the liquid phase via the luminescence of Tb(3+) complexes. The cost of the method is evaluated and compared with the Xpert MTB/RIF test endorsed by the World Health Organization.

Effect of active case finding on prevalence and transmission of pulmonary tuberculosis in Dhaka Central Jail, Bangladesh

BACKGROUND

Understanding tuberculosis (TB) transmission dynamics is essential for establishing effective TB control strategies in settings where the burden and risk of transmission are high. The objectives of this study were to evaluate the effect of active screening on controlling TB transmission and also to characterize Mycobacterium tuberculosis strains for investigating transmission dynamics in a correctional setting.

METHODS

The study was carried out in Dhaka Central Jail (DCJ), from October 2005 to February 2010. An active case finding strategy for pulmonary TB was established both at the entry point to the prison and inside the prison. Three sputum specimens were collected from all pulmonary TB suspects and subjected to smear microscopy, culture, and drug susceptibility testing as well as genotyping which included deletion analysis, spoligotyping and analysis of mycobacterial interspersed repetitive units (MIRU).

RESULTS

A total of 60,585 inmates were screened during the study period. We found 466 inmates with pulmonary TB of whom 357 (77%) had positive smear microscopy results and 109 (23%) had negative smear microscopy results but had positive results on culture. The number of pulmonary TB cases declined significantly, from 49 cases during the first quarter to 8 cases in the final quarter of the study period (p=0.001). Deletion analysis identified all isolates as M. tuberculosis and further identified 229 (70%) strains as 'modern' and 100 (30%) strains as 'ancestral'. Analysis of MIRU showed that 347 strains (85%) exhibited unique patterns, whereas 61 strains (15%) clustered into 22 groups. The largest cluster comprised eight strains of the Beijing M. tuberculosis type. The rate of recent transmission was estimated to be 9.6%.

CONCLUSIONS

Implementation of active screening for TB was associated with a decline in TB cases in DCJ. Implementation of active screening in prison settings might substantially reduce the national burden of TB in Bangladesh.

Microscopic examination and smear negative pulmonary tuberculosis in Ethiopia

INTRODUCTION

Tuberculosis causes illness among millions of people each year and ranks as the second leading cause of death from infectious disease worldwide. The aim of this study was to investigate the detection rate of microscopic examination and estimate risk of transmission of TB by smear negative pulmonary TB patients.

METHODS

A cross-sectional study and retrospective data analysis on TB were undertaken in Northwest Shewa, Ethiopia. Microscopic examination, bacterial culture and PCR were performed. The statistical analysis was made by using STATA software version 10.

RESULTS

A total of 92 suspected TB cases was included in the study. Of these, 27.17% (25/92) were positive for microscopic examination and 51% (47/92) for culture. The sensitivity and specificity of microscopic examination with 95% CI were 48.94% (34.08% to 63.93%) and 95.56% (84.82 to 99.33%), respectively. The positive and negative predictive values were 92% (73.93% to 98.78%) and 64.18% (51.53% to 75.53%), respectively. Of 8150 pulmonary TB cases in the retrospective study, 58.9% was smear negative. The proportion of TB-HIV co-infection was 28.66% (96/335).

CONCLUSION

The sensitivity of microscopic examination was 48.94% which was very low. The poor sensitivity of this test together with the advent of HIV/AIDS elevated the prevalence of smear negative pulmonary TB. This in turn increased the risk of TB transmission.

Demonstration of mycobacterium tuberculosis in sputum and saliva smears of tuberculosis patients using ziehl neelsen and flurochrome staining- a comparative study

BACKGROUND

Early detection of tuberculosis is important for reducing its morbidity and mortality especially in the patients with non-productive cough. To overcome the cumbersome process involved in collection and processing of the sputum specimen, the time consumed for reporting of sputum by Ziehl Neelsen (ZN) method and to introduce a routine screening test in suspected, symptomless tuberculosis patients, the present study was designed using saliva as diagnostic medium and Auramine Rhodamine (AR) as staining method. On review of literature, there was no study which has tried diagnosing tuberculosis using saliva with flurochrome stain; hence the present study was designed.

AIM

To introduce a routine screening test for tuberculosis patient using saliva and to determine the diagnostic efficacy of routine ZN staining method and AR fluorescent staining method in sputum and saliva smears of pulmonary tuberculosis patients.

SETTINGS AND DESIGN

Laboratory settings and Experimental design.

MATERIALS AND METHOD

Fifty smears samples of sputum and saliva of known cases of pulmonary tuberculosis were stained with routine ZN stain and other with AR fluorescent stain. All the specimens were inoculated into Lowenstein-Jensen culture media. The smears were subjected for scanning of Mycobacterium tuberculous bacilli under X 1000 magnification for ZN stain and X 400 magnification for AR stain by grid pattern proposed by National tuberculosis institute and graded by RNTCP grading system.

RESULTS

All 50 sputum samples showed 100% positivity by ZN and AR stain while only 76% positivity was seen by culture. Of the 50 saliva samples 10% cases were positive by ZN, 76% were positive by AR & 70% by culture method. Statistical analysis using chi square test was done, and the value was found to be statistically highly significant for AR staining technique. (p<0.001) CONCLUSION: Saliva can prove to be an important tool for the diagnosis as well as screening of the patients with pulmonary tuberculosis when aided with flurochrome staining method.