Reduction of the Rate of False-Positive Cultures of Mycobacterium tuberculosis in a Laboratory with a High Culture Positivity Rate

Carroll, Nora M.; Richardson, M; Engelke, E; Kock, Marianna de; Lombard, Carl; Helden, Paul D. van

doi:10.1515/cclm.2002.157

Cited by 17 publications

(11 citation statements)

References 13 publications

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“…In another published study, a South-African laboratory reported data representing a laboratory with a very high FPR and PSP[6]. In that study an average of 1186 culture samples per year were tested in the laboratory of which 55% were culture positive (PSP = 0.55, p = 1186 * 0.55 = 652).…”

Section: Resultsmentioning

confidence: 99%

The realistic performance achievable with mycobacterial automated culture systems in high and low prevalence settings

Kampen¹,

Anthony

Klatser

2010

BMC Infect Dis

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BackgroundDiagnostic tests are generally used in situations with similar pre-test probability of disease to where they were developed. When these tests are applied in situations with very different pre-test probabilities of disease, it is informative to model the likely implications of known characteristics of test performance in the new situation. This is the case for automated Mycobacterium tuberculosis (MTB) liquid culture systems for tuberculosis case detection which were developed and are widely used in low burden settings but are only beginning to be applied on a large scale in high burden settings.MethodsHere we model the performance of MTB liquid culture systems in high and low tuberculosis (TB) prevalence settings using detailed published data concentrating on the likely frequency of cross-contamination events.ResultsOur model predicts that as the TB prevalence in the suspect population increases there is an exponential increase in the risk of MTB cross-contamination events expected in otherwise negative samples, even with equivalent technical performance of the laboratories. Quality control and strict cross-contamination measures become increasingly critical as the burden of MTB infection among TB suspects increases. Even under optimal conditions the realistically achievable specificity of these systems in high burden settings will likely be significantly below that obtained in low TB burden laboratories.ConclusionsLiquid culture systems can play a valuable role in TB case detection in laboratories in high burden settings, but laboratory workers, policy makers and clinicians should be aware of the increased risks, independent of laboratory proficiency, of cross-contamination events in high burden settings.

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Section: Resultsmentioning

confidence: 99%

The realistic performance achievable with mycobacterial automated culture systems in high and low prevalence settings

Kampen¹,

Anthony

Klatser

2010

BMC Infect Dis

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“…Positive cultures were subcultured on Löwenstein-Jensen slants for genotyping by the standardized restriction fragment length polymorphism methodology based on the IS6110 transposable element (40). Standard protocols were in place to prevent cross contamination (6). Isolates were assigned to specific genotype families according to the specific IS6110 banding pattern (fingerprint).…”

Section: Methodsmentioning

confidence: 99%

Mycobacterium tuberculosis Transmission Is Not Related to Household Genotype in a Setting of High Endemicity

et al. 2009

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Among the different strains of Mycobacterium tuberculosis, Beijing has been identified as an emerging genotype. Enhanced transmissibility provides a potential mechanism for genotype selection. This study evaluated whether the Beijing genotype is more readily transmitted than other prevalent genotypes to children in contact with an adult tuberculosis (TB) index case in the child's household. We conducted a prospective, community-based study at two primary health care clinics in Cape Town, South Africa, from January 2003 through December 2004. Bacteriologically confirmed new adult pulmonary TB cases were genotyped by IS6110 DNA fingerprinting; household contacts less than 5 years were traced and screened for M. tuberculosis infection and/or disease. A total of 187 adult index cases were identified from 174 households with children aged less than 5 years. Of 261 child contacts aged 0 to 5 years, 219 (83.9%) were completely evaluated and the isolate from the index case was successfully genotyped. M. tuberculosis infection (induration of >10 mm by Mantoux tuberculin skin test) was documented in 118/219 (53.9%) children; 34 (15.5%) had radiographic signs suggestive of active TB. There was no significant difference in the ratio of infected children among those exposed to the Beijing genotype (51/89; 57.3%) and those exposed to non-Beijing genotypes (55/115; 47.8%) (odds ratio, 1.5; 95% confidence interval, 0.8 to 2.7). Genotyping was successful for six children diagnosed with active TB; the isolates from only two children had IS6110 fingerprints that were identical to the IS6110 fingerprint of the isolate from the presumed index case. We found no significant association between the M. tuberculosis genotype and transmissibility within the household. However, undocumented M. tuberculosis exposure may have been a major confounding factor in this setting with a high burden of TB.

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“…The species from these positive MGIT cultures were then determined by standard PCR (4). Negative controls were included with each batch of clinical specimens processed to monitor for laboratory cross-contamination, as recommended elsewhere (1,21). Solid LJ slants were incubated at 37°C and were examined weekly for 6 weeks or until colonies became visible.…”

Section: Methodsmentioning

confidence: 99%

Improvement in Mycobacterial Yield and Reduced Time to Detection in Pediatric Samples by Use of a Nutrient Broth Growth Supplement

et al. 2009

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There is an urgent need to improve the methods used for the bacteriological diagnosis of childhood mycobacterial disease. This study compared the mycobacterial yields and the times to detection (in days) of mycobacteria in pediatric clinical specimens by using Mycobacterial Growth Indicator Tubes (MGITs) and solid Löwenstein-Jensen (LJ) slants with and without a nutrient broth supplement. A total of 801 specimens from 493 patients were processed: 82.8% were gastric aspirate specimens, 15.6% were sputum specimens, and 1.6% were fine-needle-aspiration biopsy specimens. The mycobacterial yield obtained with MGITs (with and without nutrient broth) was 11.0%, and that obtained with LJ slants was 1.6% (P < 0.001). Of the 88 positive cultures, 62 were detected in MGITs and 73 were detected in MGITs supplemented with nutrient broth (P ‫؍‬ 0.11). The mean time to detection in MGITs (without nutrient broth) was 18.5 days, whereas it was 12.4 days in MGITs with nutrient broth (P < 0.001). Supplementation of standard MGITs improved the mycobacterial yield and significantly reduced the time to detection of mycobacteria in pediatric samples.The accurate diagnosis of childhood tuberculosis remains a major challenge (6, 24), since the paucibacillary nature of the disease in children and the difficulty of specimen collection hamper bacteriological confirmation of the diagnosis. Clinical diagnosis is complicated by the nonspecific symptoms and signs associated with pediatric tuberculosis, particularly in children with human immunodeficiency virus (HIV) infection (3, 9, 14). The traditional growth media used to cultivate mycobacteria include solid egg-based Löwenstein-Jensen (LJ) slants and Middlebrook (7H9) liquid broth-based media, such as that used in the Bactec Mycobacterial Growth Indicator Tube (MGIT) (21, 23).Growth supplements are widely used to improve the culture yield of fastidious organisms (10, 11). For the improved recovery of Mycobacterium bovis BCG, 7H9 broth (glycerol, bovine albumin fraction, glucose, sodium chloride) has been supplemented with Tween 80 (10% polyoxyethylene sorbitan monooleate solution), but the benefits appeared to be limited (7). The Bactec MGIT uses 7H9 broth supplemented with oleic acid, albumin, dextrose, and catalase (OADC) to enhance the growth of mycobacteria (21). The supplementation of 7H9 broth with a nutrient broth (modified Dubos liquid medium) containing beef extract and peptone has been recommended for the enhanced recovery of mycobacteria from inocula containing few organisms (5, 18), but data on its performance in a routine diagnostic laboratory and especially with pediatric specimens are limited. The development of tests that allow the rapid and reliable confirmation of mycobacterial infection in children has been identified as a high research priority (15,17).This study evaluated whether the addition of a meat extractbased growth supplement (Bacto TB nutrient broth; Difco Laboratories Inc., Detroit, MI) to standard culture medium improves the mycobacterial yield and the time to...

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Reduction of the Rate of False-Positive Cultures of Mycobacterium tuberculosis in a Laboratory with a High Culture Positivity Rate

Cited by 17 publications

References 13 publications

The realistic performance achievable with mycobacterial automated culture systems in high and low prevalence settings

The realistic performance achievable with mycobacterial automated culture systems in high and low prevalence settings

Mycobacterium tuberculosis Transmission Is Not Related to Household Genotype in a Setting of High Endemicity

Improvement in Mycobacterial Yield and Reduced Time to Detection in Pediatric Samples by Use of a Nutrient Broth Growth Supplement

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