Association of Xpert MTB/RIF Cycle Threshold Values with Tuberculosis Treatment Outcomes.

PURPOSE

Considering the current recommendation of the World Health Organization to replace sputum smear microscopy with Xpert MTB/RIF as an initial diagnostic test for tuberculosis (TB), and that culture takes time to provide results, the cycle threshold (C) of the Xpert test may be the only way to assess bacillary load. The objective of this study is to evaluate the association of bacillary load, measured by the Xpert C, with the TB treatment outcomes.

METHODS

In cohort study, Xpert C values were evaluated in cured and non-cured (failure and death) patients. Multivariate analysis was performed to evaluate if C is independently associated with TB treatment outcomes.

RESULTS

During this study period, 155 patients (84 cured and 71 non-cured) met the inclusion and were included in the analysis. The mean C value for Xpert MTB/RIF test was 20.7 ± 5.6 in cured patients and 17.1 ± 5.6 in non-cured patients (p < 0.0001). Previous TB was more frequent in non-cured (28.2%) than in cured patients (7.1%) (p < 0.0001). Non-cured patients were younger than cured ones (37.1 ± 13.3 vs 43.6 ± 16.2; p = 0.006). HIV was more frequent in non-cured (28.2%) than in cured patients (15.5%), although this difference was not statistically significant (p = 0.054). In multivariate analysis, C values, age, previous TB, and HIV were independently associated with non-cure.

CONCLUSIONS

Lower Xpert MTB/RIF C values were independently associated with worse treatment outcomes. The information from even a single test performed before starting treatment proved to be a relatively good predictor of TB treatment outcome.