Federica Piana

Clinical validation of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

Extrapulmonary tuberculosis (EPTB) accounts for more than 20% of tuberculosis (TB) cases. Xpert MTB/RIF (Xpert) (Cepheid, Sunnyvale, CA, USA) is a fully automated amplification system, for which excellent results in the diagnosis of pulmonary TB in highly endemic countries have been recently reported. We aimed to assess the performance of the Xpert system in diagnosing EPTB in a low incidence setting. We investigated with Xpert a large number of consecutive extrapulmonary clinical specimens (1,476, corresponding to 1,068 patients) including both paediatric (494) and adult samples. We found, in comparison with a reference standard consisting of combination of culture and clinical diagnosis of TB, an overall sensitivity and specificity of 81.3% and 99.8% for Xpert, while the sensitivity of microscopy was 48%. For biopsies, urines, pus and cerebrospinal fluids the sensitivity exceeded 85%, while it was slightly under 80% for gastric aspirates. It was, in contrast, lower than 50% for cavitary fluids. High sensitivity and specificity (86.9% and 99.7%, respectively) were also obtained for paediatric specimens. Although the role of culture remains central in the microbiological diagnosis of EPTB, the sensitivity of Xpert in rapidly diagnosing the disease makes it a much better choice compared to smear microscopy. The ability to rule out the disease still remains suboptimal.

Use of a T-cell-based test for detection of tuberculosis infection among immunocompromised patients

The aim of this study was to compare the performance of the T-SPOT.TBTM test, a T-cell-based test, with the tuberculin skin test (TST) in the diagnosis of latent tuberculosis (TB) infection. The study was carried out in 138 immunosuppressed haematology patients who had been nosocomially exposed to a case of smear-positive TB. Overall, 44.2% of the contacts were positive by T-SPOT.TBTM test, and 17.4% by TST (concordance 67.8%). The apparent prevalence of infection fell from 25.9 to 14.5% with the TST with increasing immunosuppression, although this difference was not significant. In contrast, the apparent prevalence of infection with the T-SPOT.TBTM test was unaffected at 44.6 and 44.3%, respectively. The T-SPOT.TBTM test had an overall indeterminate rate of 4.3%, and this was also unaffected by the level of immunosuppression. This study suggests that the T-SPOT.TBTM test maintains its sensitivity and performance in immunocompromised patients, identifying a large number of truly infected patients anergic to the tuberculin skin test.

Use of Genotype MTBDR Assay for Molecular Detection of Rifampin and Isoniazid Resistance in Mycobacterium tuberculosis Clinical Strains Isolated in Italy

ABSTRACT Mycobacterium tuberculosis is one of the leading causes of death worldwide, and multidrug-resistant tuberculosis (MDR-TB) is associated with a high case fatality rate. Rapid identification of resistant strains is crucial for the early administration of appropriate therapy, for prevention of development of further resistance, and to curtail the spread of MDR strains. The Genotype MTBDR (Hain Lifescience, Nehren, Germany) is a reverse hybridization line probe assay designed for the rapid detection of rpoB and katG gene mutations in clinical isolates. The ability of this technique to correctly identify resistant and MDR-TB strains was tested on 206 isolates from the Italian drug resistance surveillance system. This panel included the majority of MDR strains isolated in Italy in the past 3 years. The results of the test were compared to conventional drug susceptibility test performed on isolated strains and verified by sequencing the regions of interest of the bacterial genome. The rate of concordance between the results of the MTBDR and those obtained with “in vitro” sensitivity was 91.5% (130 of 142) for rifampin and 67.1% (116 of 173) for isoniazid. We also applied this test directly to a panel of 36 clinical specimens collected from patients with active TB. The MTBDR correctly identified the two cases of MDR-TB included in the panel. These results show that the MTBDR test is useful in the detection and management of tuberculosis when MDR disease is suspected.

Genotype MTBDRplus: a Further Step toward Rapid Identification of Drug-Resistant Mycobacterium tuberculosis

In a previous publication ([1][1]), we evaluated the Genotype MTBDR (GT-MTBDR; Hain Lifescience, Nehren, Germany) assay as a rapid diagnostic tool for multidrug resistance (MDR) detection in Mycobacterium tuberculosis isolates and clinical specimens. The main limitation of the test was the low