Tuberculosis, lung infections, and interstitial lung disease in AJRCCM 2000

Use of real time polymerase chain reaction for detection of M. tuberculosis, M. avium and M. kansasii from clinical specimens

Background

The incidence of M. tuberculosis (MTB) and non tuberculous Mycobacterium species (NTMs) like M. avium and M. kansasii has increased due to Human Immunodeficiency Virus (HIV) epidemic. Therefore accurate, rapid and cost effective methods for the identification of these NTMs and MTB are greatly needed for appropriate TB management. Thus in this study we evaluated the performance of Lightcycler® Mycobacterium detection assay to detect MTB, M. avium and M. kansasii in sputum specimens.

Methods

A total of 241 baseline minimally processed sputum specimens from individual adult TB suspected patients were analyzed by Mycobacterium detection assay (Real-time-PCR) on a LightCycler 480® while using liquid culture as a reference standard.

Results

Real time PCR had a sensitivity of 100% (95% CI 96–100) and 100% (CI 19–100) for detection of MTB and M. avium respectively. Additionally the assay had a specificity of 99% (95% CI 96–99) and 95% (95% CI 91–97) for identification of MTB and M. avium respectively. The positive predictive value (PPV) for Real time PCR to identify MTB and M. avium among the specimens was 98% (95% CI 94–99) and 15% (95% CI 2–45) respectively. The kappa statistics for Real time PCR to identify MTB and M. avium was 0.9 (95% CI 0.9–1.0) and 0.3 (95% CI–0.03–0.5) respectively. The median time to detection for Real time PCR assay was 2 hours while overall median time to detection for MGIT-positive cultures was 8 days. The sample unit cost for Real time PCR was $ 12 compared to $ 20 for the reference liquid culture.

Conclusion

The Light cycler® Mycobacterium detection assay rapidly and correctly identified MTB and M avium thus has the potential to be adopted in a clinical setting.

Elevated N-terminal pro-brain natriuretic peptide in Mycobacterium tuberculosis pulmonary infection without myocardial dysfunction

Increased levels of N-terminal pro-brain natriuretic peptide (NT pro- BNP) in infectious settings may not reflect myocardial depression. In addition to NT pro-BNP measurement, clinical assessment remains a valuable tool for diagnosis and prognosis of heart failure. A case of excessively increased NT pro-BNP level associated with Mycobacterium tuberculosis infection that was not indicative of myocardial dysfunction is described.

Detection and differentiation of Mycobacterium tuberculosis and nontuberculous mycobacterial isolates by real-time PCR

Mycobacteria cause a variety of illnesses that differ in severity and public health implications. The differentiation of Mycobacterium tuberculosis from nontuberculous mycobacteria (NTM) is of primary importance for infection control and choice of antimicrobial therapy. Despite advances in molecular diagnostics, the ability to rapidly diagnose M. tuberculosis infections by PCR is still inadequate, largely because of the possibility of false-negative reactions. We designed and validated a real-time PCR for mycobacteria by using the LightCycler system with 18 reference strains and 168 clinical mycobacterial isolates. All clinically significant mycobacteria were detected; the mean melting temperatures (with 99.9% confidence intervals [99.9% CI] in parentheses) for the different mycobacteria were as follows: M. tuberculosis, 64.35 degrees C (63.27 to 65.42 degrees C); M. kansasii, 59.20 degrees C (58.07 to 60.33 degrees C); M. avium, 57.82 degrees C (57.05 to 58.60 degrees C); M. intracellulare, 54.46 degrees C (53.69 to 55.23 degrees C); M. marinum, 58.91 degrees C (58.28 to 59.55 degrees C); rapidly growing mycobacteria, 53.09 degrees C (50.97 to 55.20 degrees C) or 43.19 degrees C (42.19 to 44.49 degrees C). This real-time PCR assay with melting curve analysis consistently accurately detected and differentiated M. tuberculosis from NTM. Detection of an NTM helps ensure that the negative result for M. tuberculosis is a true negative. The specific melting temperature also provides a suggestion of the identity of the NTM present, when the most commonly encountered mycobacterial species are considered. In a parallel comparison, both the LightCycler assay and the COBAS Amplicor M. tuberculosis assay correctly categorized 48 of 50 specimens that were proven by culture to contain M. tuberculosis, and the LightCycler assay correctly characterized 3 of 3 specimens that contained NTM.