Feasibility and Sensitivity of Saliva GeneXpert MTB/RIF Ultra for Tuberculosis Diagnosis in Adults in Uganda

ABSTRACT 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) testing on saliva for active tuberculosis (TB) disease among consecutive adults undergoing diagnostic evaluation. We calculated sensitivity to determine the diagnostic performance in comparison to that of the composite reference standard of Mycobacterium tuberculosis liquid and solid cultures on two spot sputum specimens. GeneXpert Ultra on saliva had a sensitivity of 90% (95% confidence interval [CI], 81-96%); this was similar to that of sputum fluorescence smear microscopy (FM) of 87% (95% CI, 77-94%). Sensitivity 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% lower (95% CI for difference 14-77%, p<0.0001) among sputum microscopy positive (96%, 95% CI 87-99%) than among sputum microscopy negative patients (50%, 95% CI 19-81%). Semi-quantitative Xpert grade was higher in sputum than in paired saliva samples from the same patient. In conclusion, saliva specimens appear to be feasible and similarly sensitive to sputum for active TB diagnosis using molecular testing, suggesting promise as a non-sputum diagnostic test for active TB in high-burden settings.