Abstract
Most cases of multidrug-resistant (MDR) tuberculosis (TB) are never diagnosed (328,300 of the ∼490,000 cases in 2016 were missed). The Xpert MTB/RIF assay detects resistance only to rifampin, despite ∼20% of rifampin-resistant cases being susceptible to isoniazid (a critical first-line drug).
Most cases of multidrug-resistant (MDR) tuberculosis (TB) are never diagnosed (328,300 of the ∼490,000 cases in 2016 were missed). The Xpert MTB/RIF assay detects resistance only to rifampin, despite ∼20% of rifampin-resistant cases being susceptible to isoniazid (a critical first-line drug). Consequently, many countries require further testing with the GenoType MTBDR
plus
assay. However, MTBDR
plus
is not recommended for use on smear-negative specimens, and thus, many specimens require culture-based drug susceptibility testing. Furthermore, MTBDR
plus
requires specialized expertise, lengthy hands-on time, and significant laboratory infrastructure and interpretation is not automated. To address these gaps, we evaluated the accuracy of the FluoroType MTBDR (FluoroType) assay. Sputa from 244 smear-positive and 204 smear-negative patients with presumptive TB (Xpert MTB positive,
n
= 343) were tested. Culture and MTBDR
plus
on isolates served as reference standards (for active TB and MDR-TB, respectively). Sanger sequencing and MTBDR
plus
, both of which were performed on sputa, were used to resolve discrepancies. The sensitivity of FluoroType for the detection of
M. tuberculosis
complex was 98% (95% confidence interval [CI], 95 to 99%) and 92% (95% CI, 84 to 96%) for smear-positive and smear-negative specimens, respectively (232/237 versus 90/98 specimens;
P
< 0.009). The sensitivity and specificity for smear-negative specimens were 100% and 97%, respectively, for rifampin resistance; 100% and 98%, respectively, for isoniazid resistance; and 100% and 100%, respectively, for MDR-TB. FluoroType identified 98%, 97%, and 97% of the
rpoB
,
katG
, and
inhA
promoter mutations, respectively. FluoroType has excellent sensitivity with sputa equivalent to that of MTBDR
plus
with the isolates and can provide rapid drug susceptibility testing for rifampin and isoniazid. In addition, the capacity of FluoroType to simultaneously identify virtually all mutations in the
rpoB
,
katG
, and
inhA
promoter may be useful for individualized treatment regimens.
