Gene Xpert MTB/RIF Ultra utility for the diagnosis of pulmonary tuberculosis. Study in Uruguayan population, January-December 2021

Abstract

Tuberculosis, disease caused by Mycobacterium tuberculosis complex, is a global public health problem,
with an increasing incidence in Uruguay for two decades, currently regressing due to the COVID-19
pandemic. The CepheidTM GeneXpert MTB/RIF® closed real-time polymerase chain reaction platform
provides greater sensitivity and specificity to TBC diagnostic in comparison to the bacilloscopy. The
Ultra® version has been available in the country since 2020, and it shows a performance very similar to
the culture.
The present observational, analytical and cross-sectional study, with a sample of 2,174 subjects taken
from the primary source TBSoft®, management software of the National Reference Laboratory of the
CHLA-EP, develops an evaluation of the diagnostic performance of Ultra compared to the culture’s
performance for different types of respiratory samples, and it includes the contribution of the trace
results detection to the study.
Among the total of patient samples, Xpert Ultra showed a sensitivity of 95.32% and specificity of 95.71%
compared to the culture. Additionally, in terms of diagnostic security, the positive predictive value of
Ultra falls 4.24%, while the negative predictive value improves 0.09% (Table 5). When different samples
are analyzed side by side, results become heterogeneous. The trace results detection adds a diagnostic
sensibility of 2.15% (Table 6) to the sputum samples and 0% in bronchoalveolar lavage samples (Table 7).
In conclusion, Xpert Ultra shows a better diagnostic performance compared to its predecessor (Gene XPert), both being compared against culture in solid medium as the gold standard diagnostic method. In
terms of validity, the new XPert Ultra version improves its performance with a great S/E ratio. In terms of
security, it improves with a great PPV/NPV ratio