Byanyima et al- Feasibility and sensitivity of saliva GeneXpert MTBRIF Ultra for tuberculosis diagnosis in Ugandan adults

The objective of this prospective, observational study carried out at
China-Uganda Friendship Hospital-Naguru in Kampala, Uganda, was to
determine the performance of GeneXpert MTB/RIF Ultra (Xpert Ultra)
molecular testing on saliva for active tuberculosis (TB) disease among
consecutive adults undergoing TB diagnostic evaluation who
were Xpert Ultra positive on sputum. We
calculated sensitivity to determine TB diagnostic performance in
comparison to a composite reference standard of Mycobacterium
tuberculosis (Mtb) liquid and solid cultures on two spot
sputum specimens. Xpert Ultra on a single saliva sample had
a sensitivity of 90% (95% CI 81-95%) relative to the composite
sputum culture-based reference standard, similar to the composite
sensitivity of 87% (95% CI, 77-94%) fluorescence smear microscopy (FM) for
acid-fast bacilli on two sputa. The sensitivity of salivary Xpert Ultra
was 24% lower (95% CI for difference 2-48%, p=0.003) among persons living
with HIV (71%, 95% CI 44-90%) than among persons living without HIV (95%,
95% CI 86-99%) and 46% higher (95% CI 14-77%, p<0.0001) among
FM-positive (96%, 95% CI 87-99%) than among
FM-negative patients (50%, 95% CI
19-81%) patients. Semi-quantitative Xpert
Ultra  grade was systematically higher in sputum than in
a paired saliva sample from the same patient. In conclusion,
molecular testing of saliva for active TB diagnosis was feasible and
almost as sensitive as molecular testing of sputum in a high TB-burden
setting.