Abstractobjective The Xpert MTB/Rif, with a detection limit of 131 CFU/ml, plays a valuable role in the diagnosis of extrapulmonary tuberculosis, both susceptible and resistant. This study aims at evaluating the Xpert MTB/Rif for the same, at a tertiary care centre in south India, assessing it against both culture and a composite gold standard (CGS).methods We tested consecutive samples from patients suspected of extrapulmonary tuberculosis with Xpert MTB/Rif, evaluated its sensitivity and specificity against solid and/or liquid culture and CGS. An individual analysis of different sample types (tissue biopsies, fluids, pus, lymph node biopsies and CSF) given an adequate sample size, against both culture and CGS, was also performed.results In total, 494 samples were analysed against culture. Compared to culture, the sensitivity of Xpert MTB/Rif was 89% (95% CI 0.81-0.94) and its specificity was 74% (95% CI 0.70-0.78). When Xpert MTB/Rif was compared to the CGS, pooled sensitivity was 62% (95% CI 0.56-0.67) and specificity was 100% (95% CI 0.91-1.00).conclusion This assay performs better than the currently available conventional laboratory methods. The rapidity with which results are obtained is an added advantage, and its integration into a routine diagnostic protocol must be considered.keywords tuberculosis, extrapulmonary, Xpert MTB/Rif

Owing to the burden of multidrug-resistant tuberculosis, molecular techniques have been approved by the WHO for the rapid diagnosis of the same. The objectives of this prospective, diagnostic study, conducted at Christian Medical College, a tertiary care center in South India, were to compare the performance of line probe assay (GenoTypeMTBDRplus) with culture, as well as the Xpert MTB/Rif assay on sputum samples. Ninety-one consecutive suspects of multidrug-resistant pulmonary tuberculosis patients from January 2013 to June 2013 were enrolled in this study and the results of line probe assay compared to culture and Xpert MTB/Rif. Compared to culture, the assay demonstrated a sensitivity and specificity of 81.5% (95%CI 67.4-91.1%) and 87.5% (95%CI 71-96.5%) for the detection of tuberculosis, with sensitivity and specificity of 100% (95%CI 85.2-100%) and 93.8% (95%CI 69.8-99.8%), respectively, for rifampicin resistance. For isoniazid resistance, sensitivity and specificity were 89.3% (95%CI 71.8-97.7%) and 100% (95%CI 71.5-100%), respectively. Compared to Xpert MTB/Rif assay, the assay showed a sensitivity of 80% (95%CI 68.2-88.9%) and specificity of 100% (95%CI 85.8-100%) for the detection of tuberculosis a sensitivity of 94.3% (95%CI 80.8-99.3%) and specificity of 94.1% (95%CI 71.3-99.9%) for rifampicin resistance was attained. This assay performed well on smear positive samples, but poorly on smear negative and scanty samples, and can serve as a rapid diagnostic tool, particularly in isoniazid monoresistant cases of tuberculosis, which are not diagnosed by Xpert MTB/Rif.

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BackgroundRapid antigen testing is widely used as a way of scaling up population-level testing. To better inform antigen test deployment in Australia, we evaluated 22 commercially available antigen tests against the currently circulating delta variant, including an assessment of culture infectivity.MethodsAnalytical sensitivity was evaluated against SARS-CoV-2 B.1.617.2 (Delta), reported as TCID50/mL, cycle threshold (Ct) and viral load (RNA copies/mL). Specificity was assessed against non-SARS-CoV-2 viruses. Clinical sensitivity and correlation with cell culture infectivity was assessed using the Abbott PanBio™ COVID-19 Ag test.ResultsNineteen kits consistently detected SARS-CoV-2 antigen equivalent to 1.3 × 106 copies/mL (5.8 × 103 TCID50 /mL). Specificity for all kits was 100%. Compared to RT-PCR the Abbott PanBio™ COVID-19 Ag test was 52.6% (95% CI, 41.6% to 63.3%) concordant, with a 50% detection probability for infectious cell culture at 5.9 log10 RNA copies/mL (95% CI, 5.3 to 6.5 log10 copies/mL). Antigen test concordance was 97.6% (95% CI, 86.3% to 100.0%) compared to cell culture positivity.ConclusionsAntigen test positivity correlated with positive viral culture, suggesting antigen test results may determine SARS-CoV-2 transmission risk. Analytical sensitivity varied considerably between kits highlighting the need for ongoing systematic post-market evaluation to inform test selection and deployment.