S112 Diagnostic accuracy of Xpert Ultra for the detection of MTB in bronchoalveolar lavage samples for pulmonary tuberculosis in a tertiary TB centre

<h3>Introduction</h3> The emergence of the new rapid polymerase chain reaction (PCR) test Xpert Ultra (Cepheid, Sunnyvale, CA, USA) has been shown to be more sensitive compared to smear microscopy as well as to the previous Xpert MTB/RIF for the detection of <i>Mycobacterium tuberculosis</i> (MTB) in sputum. This has not been validated in bronchoalveolar lavage (BAL) samples for pulmonary TB. <h3>Aims</h3> To analyse the diagnostic accuracy of Xpert Ultra for the detection of MTB in BAL samples for pulmonary tuberculosis against conventional modalities and against a clinical diagnosis of TB in a tertiary centre. <h3>Method</h3> A retrospective data analysis of 213 BAL samples collected from January 2018 to 2019 from a tertiary TB centre of which the results for Xpert Ultra, smear microscopy, culture and clinical outcomes were reviewed. Patient demographics and clinical phenotypes were collected from patient records and the London TB Registry. This was correlated to clinical diagnosis and treatment outcomes. <h3>Results</h3> A total of 1008 Xpert Ultra were performed for possible TB of which 213 were in BAL samples. For these, the mean age was 53 years (range 8 to 91), with 132 males, 81 females. There were 15 patients with HIV and 4 with previous TB in this cohort. The diagnostic accuracy tests are summarised in table 1. A total of 19 patients were culture positive with the mean day to culture being 17.4 days (IQR 12–21) of which 14 were positive for Xpert Ultra whereas only 10 were positive for smear. 2 ‘trace’ patient results were ultimately culture positive, one being smear negative and the other being smear positive but with isoniazid mono-resistance. 1 had MDR-TB which was Xpert Ultra positive but smear negative hence Xpert Ultra allowed a substantive lead time to MDR-TB treatment prior to culture positivity and subsequent sensitivities. <h3>Conclusion</h3> Xpert Ultra offers a point-of-care diagnostic test for MTB as well as rifampicin resistance in sputum samples but it also appears to offer a rapid and significant diagnostic advantage over smear in BAL samples in both culture proven and clinically defined pulmonary TB.