Evaluation Of The Operating Characteristics Of GeneXpert® MTB/RIF At A National Reference Center: Hospital Universitario San Ignacio, Bogota, Colombia

Background: Early detection is essential to reduce transmission from tuberculosis (TB) globally. Conventional tests for identification of TB take 2 to 6 months and have a low performance in patients with HIV. In Colombia, where the prevalence of TB is 39 cases per 100,000 population, the GeneXpert MTB/RIF test could be a strategy for early detection or discarding of infection.

Methods: Retrospective study to evaluate the diagnostic performance of GeneXpert MTB/RIF in respiratory symptomatic patients,recruited from May 2013 to May 2016, in a national reference center Hospital Universitario San Ignacio in Colombia, with analysis according to the result of the smear and the state of immunosuppression of subjects, taking as reference cultures and susceptibility tests that were performed in all subjects. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratios (LR) and area under the ROC curve (ROC-AUC) were calculated.

Results: The study group included 468 patients who underwent GeneXpert MTB/RIF test and culture for TB in a respiratory secretion. 51% of subjects had some form of immunosuppression, HIV infection being in 52% of cases. In general sensitivity, specificity, PPV, NPV, LR+ and LR-for GeneXpert MTB/RIF were 90%, 99%, 92%, 99%, 90 and 0.1, respectively. There was complete concordance between tests in patients with positive smears. In patients with negative smears sensitivity, specificity, PPV, NPV, LR+ and LR- of GeneXpert MTB/RIF were 88%, 99%, 86%, 99%, 88 and 0.12, respectively. Within this group for patients with HIV sensitivity, specificity, PPV, NPV, LR+ and LR- of GeneXpert MTB/RIF were 89%, 99%, 89%, 99%, 95 and 0.11 and for patients HIV negative were 88%, 99%, 96%, 99%, 275 and 0.12, respectively (table). For rifampin resistance sensitivity, specificity, PPV and NPV were 100%, 96%, 50% and 100%, respectively. The AUC-ROC was 0.93 in general, 0.93 for patients with negative smears without HIV and 0.94 for patients with negative smears with HIV infection.