Improvement of Mycobacterium tuberculosis detection by Xpert MTB/RIF Ultra: a head to head comparison on Xpert-negative samples

Sixty-eight decontaminated frozen samples (36 respiratory and 32 non-respiratory) collected over a 4-year period which were smear-negative, Xpert-negative but MTB culture-positive, were tested with Xpert MTB/RIF Ultra at the Unit of Microbiology of the S. Orsola-Malpighi University Hospital in Bologna (Italy). Database reports smear microscopy, mycobacterial culture, Xpert and Xpert Ultra results, Rif detection,semi-quantitative load and Ct results of IS1081, IS6110 and rpoB genes, time to positivity, time of storage.