Aptamer-Based TB Antigen Tests for the Rapid Diagnosis of Pulmonary Tuberculosis: Potential Utility in Screening for Tuberculosis.

Pulmonary tuberculosis is the most common manifestation of tuberculosis, and to this day, sputum smear microscopy remains the most widely used diagnostic test in resource-limited settings despite its suboptimal sensitivity. Here we report the development of two DNA aptamer-based diagnostic tests, namely aptamer linked immobilized sorbent assay (Aptamer ALISA) and electrochemical sensor (ECS), for the direct detection of a TB biomarker HspX in sputum. First we compared the performance of Aptamer ALISA with anti-HspX polyclonal antibody-based enzyme linked immunosorbent assay (Antibody ELISA) in a blinded study of 314 sputum specimens. Aptamer ALISA displayed a high sensitivity of 94.1% (95% CI 86.8-98%) as compared to 68.2% sensitivity (95% CI 57.2-77.9%) of Antibody ELISA ( p-value < 0.05) using culture as the reference standard without compromising test specificity of 100%. Out of nine smear-negative culture-positive samples, six were positive by Aptamer ALISA and only two were detected by Antibody ELISA. ALISA detected as positive 80 of 85 culture-positive TB as compared to 57 of 81 diagnosed as TB by X-ray ( p-value < 0.0001). These findings demonstrate the superiority of the aptamer-based test over smear microscopy, antibody-based ELISA, and chest X-ray for TB detection ( p-value < 0.0001 for all). Further, we have developed a ∼30 min point-of-care ECS test that discriminates between tuberculous and nontuberculous sputum with a sensitivity of ∼92.3% and specificity of 91.2%. The tests developed in the current study cost ∼$1-3/test and have potential utility in active case finding in high-risk groups and screening for pulmonary TB among presumptive TB subjects.