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Xpert MTB/RIF Ultra versus Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

M T Tórtola(1,2) J Vegué(2) P Martínez(2) M Gallardo(2) C Escartín(2)

1:Universidad Autónoma de Barcelona; 2:Microbiology Service. Hospital University Vall d’Hebron

Diagnosis of extrapulmonary tuberculosis (EPTB) is difficult due to the different clinical presentations, the need for invasive procedures to secure appropriate samples and the paucibacillary load in such samples. In recent decades, molecular techniques have been developed to improve its diagnosis. One of them is the GeneXpert platform. The aim of this study was to compare Xpert ultra versus Xpert MTB/RIF in samples from patients with suspected extrapulmonary tuberculosis.

A total of 2.186 samples from 1.924 patients was studied. All samples were collected between 2014 and 2022. The samples were decontaminated using the method described by Kent and Kubica. Following decontamination and concentration, the sediment of the specimens was used for microscopic examination, culture, and GenXpert MTB/RIF (Cepheid, Sunnyvale, CA) or Xpert Ultra during the years 2014-2019 and 2020-2022, respectively.

The overall sensitivity and specificity of the Xpert MTB/RIF and Xpert Ultra assay were 67.8%, 97.9% and 81,2%, 98,3% respectively (p=0.026). The samples studied with Xpert MTB/RIF and Xpert Ultra were 1.232 (56.3%) and 954 (43.6%) respectivelly. Smear microscopy was positive in 25 (1.14%) samples and negative in 2.161 (98.8%) samples. The largest number of samples studied corresponded to lymph node biopsies (766/35%), pleural fluid (389/17.7%) and cerebrospinal fluid (335/15.3%). The sensitivity with the Xpert Ultra for lymph node biopsies and pleural fluid with smear microscopy negative was 75% and 100% while with the Xpert MTB/RIF was 62.8% and 46.15% respectively. This increase in sensitivity of the Xpert Ultra was statistically significant (p<0.05).

Xpert Ultra has improved the diagnosis of extrapulmonary tuberculosis.

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