Rapid diagnosis of tuberculosis using ex vivo host biomarkers in sputum

To the Editor: Tuberculosis continues to be a major public health problem in developing countries [1]. One of the roadblocks in reducing tuberculosis transmission is the lack of accurate laboratory-free diagnostic tests for use at the point of care. If tuberculosis is to be eliminated, we need a robust, low-cost and safe point-of-care diagnostic test, which in turn requires identification of appropriate biomarkers [2]. Rapid tests based on microfluidics (lateral flow tests) hold great promise for tuberculosis diagnostics. They are easy to use, cheap, provide an answer within minutes, do not require specialised equipment and are stable at room temperature, making them ideal for use in high tuberculosis burden, resource-poor settings. To date, however, no such test has been developed for tuberculosis due to lack of sensitivity related to the markers and/or sample type. Development of tests based on host biomarkers requires evaluation of different sample types [3]–[5] and markers other than interferon (IFN)-γ [5] to provide differential diagnosis of active tuberculosis, latent infection and other respiratory disorders. We have previously shown that a combination of three host factors in pleural fluid resulted in 96% correct classification of tuberculosis among other respiratory diseases (ORD) (including bacterial pneumonia) regardless of HIV status [6]. However, this sample type is not easy to obtain and we therefore wanted to determine if we could use ex vivo sputum, which is noninvasive and easy to obtain in adult pulmonary tuberculosis patients. Subjects were consecutively recruited from the outpatient clinic and ward at the Medical Research Council Unit, Fajara, the Gambia. All subjects were adults (≥18 years of age) with symptoms suggestive of tuberculosis. Subjects were subsequently classified into two groups: those with culture-confirmed tuberculosis and those with ORD. 75% of the tuberculosis and …