Impact of sputum gross appearance and volume on smear positivity of pulmonary tuberculosis: a prospective cohort study

Yoon, Soon Ho; Lee, Nyoung Keun; Yim, Jae Joon

doi:10.1186/1471-2334-12-172

Cited by 29 publications

(26 citation statements)

References 13 publications

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“…In a large, prospective study by Warren et al, the sensitivity of smears during a 39-month period (n ϭ 1,849) using Ն5.0 ml of sputum was 92.0%, significantly greater (P Ͻ 0.001) than the sensitivity of 72.5% in a previous 24-month period (n ϭ 3,486) when all specimens were processed regardless of volume (14). In a recent study, sputum gross appearance and volume were associated with direct smear positivity (15). A related issue in TB diagnostic studies is the difficulty in accurately evaluating lowvolume samples, as specimen splitting is likely to provide a more robust comparison of diagnostic performance than testing sister samples from the same patient (16).…”

Section: Discussionmentioning

confidence: 99%

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Jones-López¹,

Manabe²,

Palaci³

et al. 2014

J Clin Microbiol

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f Smear microscopy has suboptimal sensitivity, and there is a need to improve its performance since it is commonly used to diagnose tuberculosis (TB). We prospectively evaluated the diagnostic accuracy of the small membrane filtration (SMF) method, an approach that uses a vacuum manifold and is designed to concentrate bacilli onto a filter that can be examined microscopically. We enrolled hospitalized adults suspected to have pulmonary TB in Kampala, Uganda. We obtained a clinical history and three spontaneously expectorated sputum specimens for smear microscopy (direct, concentrated, and SMF), MGIT T uberculosis (TB) remains a major global health problem (1). Despite the recent development of new diagnostic modalities (2), in much of the world, the diagnosis of pulmonary TB continues to rely on microscopic examination of stained sputum smears. Acid-fast bacillus (AFB) smear microscopy is inexpensive and rapid, has high positive predictive value in areas of high TB prevalence, and identifies the most infectious subset of TB patients (3). However, despite its widespread use, the sensitivity of routine smear microscopy ranges from 20% to 75% and its performance is highly dependent on the number of bacilli in the specimen (4, 5). The sensitivity of smear microscopy is notably poor in populations with a high burden of TB and under conditions that lead to a low mycobacterial burden in clinical specimens, such as in children, patients with HIV/AIDS-associated TB, early TB disease, or pleural or meningeal TB (2, 4). Overall, the suboptimal sensitivity of smear microscopy results in delays in diagnosis with consequent disease progression, poor outcomes, and uninterrupted transmission of M. tuberculosis (6).Concentration of bacilli is a strategy to increase the sensitivity of sputum AFB smear microscopy. Concentration through centrifugation or gravity sedimentation results in modest (5 to 10%) gains in sensitivity (3), but centrifugation carries a risk of aerosol generation and requires equipment, while gravity sedimentation increases the specimen testing time. The small membrane filtration (SMF) method uses a vacuum manifold to concentrate bacilli present in a clinical sample onto a small membrane that can subsequently be stained and examined microscopically for AFB. By increasing the concentration of bacilli in the microscopic field, the SMF method may increase the sensitivity of smear microscopy. The SMF method reduces biohazard potential through the use of bleach (sodium hypochlorite), which kills M. tuberculosis bacilli (7), and a sealed processing system that limits sample manipulation, and thus, the method might be amenable for use in the existing global network of facilities that already use smear microscopy. Two prior studies using earlier, more rudimentary (full manual operation) versions of the vacuum manifold showed promising results for both and HIV-infected (9) patients, but the processing failure rates were high, since 5 to 20% of samples failed to fully filter through the membrane.This study prospectiv...

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Section: Discussionmentioning

confidence: 99%

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Jones-López¹,

Manabe²,

Palaci³

et al. 2014

J Clin Microbiol

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“…11 In this study, Xpert sensitivity was 18-20% lower in mucosalivary than in mucopurulent samples, independently of previous TB treatment status. In previous studies, purulent samples have been shown to increase the yield of sputum AFB smear 12 and culture, 10,11 but data on how sample quality may impact Xpert performance are scarce. Furthermore, because males expectorated larger volumes and more purulent sputum samples than females, the interpretation of the true impact of specimen quality in our study was further confounded.…”

Section: Discussionmentioning

confidence: 99%

“…[6][7][8][9] Patients with discordant cultureÀ, Xpertþ results are currently thought to have 'false-positive' Xpert results as a result of remnant, non-viable bacilli after anti-tuberculosis treatment. 8,9 However, despite its known impact on the yield of other diagnostic methods such as AFB smear microscopy and culture, [10][11][12] limited attention has been placed on the effect of sputum quality on Xpert diagnostic performance. In the present study, we report our experience with Xpert among patients with suspected pulmonary TB in Southwestern Uganda.…”

Section: Since Its Introduction In 2010mentioning

confidence: 99%

Effect of previous treatment and sputum quality on diagnostic accuracy of Xpert^® MTB/RIF

Acuña-Villaorduña

Orikiriza

Nyehangane

et al. 2017

int j tuberc lung dis

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“…In this study, we found a 67.4% sensitivity of a single SMF in the HIV-infected cohort, which, although better than the 48.5% reported on the first prospective evaluation (17), still remains significantly lower than the 82% to 89% sensitivity found in the initial proof-of-concept studies (15,16). Quality and volume of sputum specimens are known to predict smear positivity, as shown by a recent study from Korea where sputum volumes Ͼ4 ml were more likely to yield positive results (26). We hypothesized that the dilution protocol used in the Kampala study might have affected the SMF performance when distilled water was added to the samples to achieve a 5-ml volume.…”

Section: Discussionmentioning

confidence: 60%

Diagnostic Accuracy of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis in a High-HIV-Prevalence Setting

et al. 2016

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g Sputum acid-fast bacilli (AFB) smear microscopy has suboptimal sensitivity but remains the most commonly used laboratory test to diagnose pulmonary tuberculosis (TB). We prospectively evaluated the small membrane filtration (SMF) method that concentrates AFB in a smaller area to facilitate detection to improve the diagnostic performance of microscopy. We enrolled adults with suspicion of pulmonary TB from health facilities in southwestern Uganda. Clinical history, physical examination, and 3 sputum samples were obtained for direct fluorescent AFB smear, SMF, Xpert MTB/RIF, and MGIT culture media. Sensitivity and specificity were estimated for SMF, AFB smear, and Xpert MTB/RIF, using MGIT as the reference standard. Direct acid-fast bacilli (AFB) smear microscopy of unconcentrated sputum has been the mainstay of tuberculosis (TB) diagnosis for more than a century, especially in resource-constrained settings, where more than 90% of the cases and TB-related deaths occur (1). Direct AFB smear microscopy is inexpensive, is specific in high-TB-prevalence settings, and can rapidly identify the most infectious patients (i.e., sputum AFB positive) (2, 3). However, sputum AFB has suboptimal sensitivity, particularly in populations with a low Mycobacterium tuberculosis bacillary load in sputum (i.e., paucibacillary TB), such as children, those with extrapulmonary TB, and persons with HIV infection (4). Overall, the diagnostic sensitivity of the direct sputum AFB smear ranges between 30% and 75%, often leading to delayed diagnosis, continued transmission, and poor outcomes (5, 6).Several methods have been evaluated to increase the sensitivity of smear microscopy. These include the use of chemicals, such as sodium hydroxide (NaOH), N-acetyl-L-cysteine (NALC), or sodium hypochlorite (bleach), to liquefy and concentrate sputum (7-9), use of light-emitting diodes to improve visualization (10, 11), and physical measures, such as centrifugation or gravity sedimentation (12, 13). A systematic review showed that sputum centrifugation plus a chemical (NALC or NaOH) can improve the yield of smear microscopy up to 39% (14). However, centrifuges are expensive, require electricity, and are biosafety level 3, as they carry a potential risk of aerosolization, and some bacilli may be lost in the supernatant. In general, given the widespread use and operational benefits of smear microscopy, any technology that increases its yield would be of great value.The small membrane filtration (SMF) is a novel method that concentrates bacilli from clinical samples by filtrating the sputum digests through a 25-mm-diameter polycarbonate membrane filter (15). After filtration, the membrane is fixed to a glass slide that can be stained and examined for AFB with standard methods. In the initial proof-of-concept studies that used individual filters connected to a rudimentary, plastic-made vacuum manifold, SMF showed an absolute incremental yield of up to 40% compared to direct smear, but the filtration failure rate (5% to 20%) was unac-

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Impact of sputum gross appearance and volume on smear positivity of pulmonary tuberculosis: a prospective cohort study

Cited by 29 publications

References 13 publications

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Effect of previous treatment and sputum quality on diagnostic accuracy of Xpert^® MTB/RIF

Diagnostic Accuracy of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis in a High-HIV-Prevalence Setting

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Impact of sputum gross appearance and volume on smear positivity of pulmonary tuberculosis: a prospective cohort study

Cited by 29 publications

References 13 publications

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Prospective Cross-Sectional Evaluation of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis

Effect of previous treatment and sputum quality on diagnostic accuracy of Xpert® MTB/RIF

Diagnostic Accuracy of the Small Membrane Filtration Method for Diagnosis of Pulmonary Tuberculosis in a High-HIV-Prevalence Setting

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Effect of previous treatment and sputum quality on diagnostic accuracy of Xpert^® MTB/RIF