Time to appropriate treatment in patients with multidrug-resistant tuberculosis in South Korea: Are we still in 2010?

Sensitivity and specificity of the mean corpuscular volume and CD4/CD8 ratio in discriminating between rifampicin resistant and rifampicin sensitive tuberculosis

Background

There is need for simple, cost effective and widely available point of care tests for low level health facilities in developing countries to screen for drug resistant tuberculosis (TB) after bacteriological confirmation of TB by smear microscopy. We evaluated the sensitivity and specificity of the mean corpuscular volume (MCV) and CD4/CD8 ratio in discriminating between rifampicin resistant (RR-TB) and rifampicin sensitive (RS-TB) tuberculosis.

Methods

We performed a secondary analysis of data from a cross sectional study that enrolled adult participants with bacteriologically confirmed pulmonary TB at a national tuberculosis treatment center in Uganda. Blood samples were tested for CD4 and CD8 cell counts, HIV serology and a full hemogram. Rifampicin sensitivity and the bacillary load grade were determined by Xpert MTB/RIF®. Fifty-five participants that had RR-TB (cases) were matched with 110 participants that had RS-TB (controls) for age, sex and HIV status in a ratio of 1:2 respectively. Sensitivity (Se), specificity (Sp), area under curve (AUC) analysis and determination of optimal cut-offs were performed using receiver operating characteristic curves.

Results

Cases differed from controls with respect to residence (p = 0.031), bacillary load grade (p < 0.010) and MCV (p = 0.021). The Se, Sp and AUC of the MCV (cut-off of > 74.6 femtolitres (fl)) were 88.9%, 34% and 0.607 (p = 0.021) respectively for RR-TB. Among HIV positive participants, the respective Se, Sp and AUC of the MCV for RR-TB (cut-off of > 72.5 fl) were 97.2%, 22.2% and 0.608 (p = 0.061). The respective Se, Sp and AUC of the CD4/CD8 ratio (cut-off of > 0.40) were 67.3%, 50.0% and 0.559 (p = 0.199) on the overall and 54.1%, 71.6% and 0.628 (p = 0.024) among the HIV positive participants for RR-TB.

Conclusion

The MCV had a high sensitivity but very low specificity for RR-TB. The CD4/CD8 ratio had a low sensitivity and specificity for RR-TB among HIV positive individuals. The utility of either test is low due to low diagnostic accuracy.

Impact of Molecular Drug Susceptibility Testing on the Time to Multidrug-resistant Tuberculosis Treatment Initiation

BACKGROUND

The purpose of this study was to evaluate the current status and trends in the coverage of molecular drug susceptibility testing (mDST), and the impact of mDST on the time to multidrug-resistant tuberculosis (MDR-TB) treatment initiation in Korea.

METHODS

We included confirmed rifampin-resistant (RR)/MDR-TB patients who submitted application forms for novel drug uses to the National TB Expert Review Committee from September 1, 2016 to November 30, 2019. We retrospectively reviewed their medical records.

RESULTS

Of the 621 MDR/RR-TB patients, mDST was performed in 442 (71.2%); Xpert MTB/RIF (Xpert) alone in 109 (17.6%), MTBDRplus line probe assay (LPA) alone in 199 (32.0%), and both Xpert and LPA in 134 (21.6%) patients. The coverage rate of mDST has gradually increased to 70% in 2015, 50.7% in 2016, 67.9% in 2017, 75.2% in 2018, and 79.4% in 2019 (P for trend < 0.001). Median time to MDR-TB treatment initiation was 35 days (interquartile range_25-75 0-72), which has gradually decreased during the study period (P < 0.001). Independent predictors of shorter time to MDR-TB treatment initiation were retreatment case (adjusted hazard ratio [aHR], 1.30; 95% confidence interval [CI], 1.10-1.54), Xpert testing (aHR, 2.42; 95% CI, 2.03-2.88), and LPA testing (aHR, 1.83; 95% CI, 1.55-2.16). Transfer to another healthcare facility was inversely related to shorter time to treatment initiation (aHR, 0.74; 95% CI, 0.63-0.88).

CONCLUSION

mDST coverage is gradually increasing and contributes to reducing the time to MDR-TB treatment initiation. Further efforts are needed to achieve universal access to mDST and to properly integrate mDST into routine clinical practice.