Use of fluorescen diacetate vital staining for the early detection of rifampicin resistance in tuberculosis patients in Mali

As recommended by world health organization (WHO) guidelines, the success of tuberculosis (TB) treatment is measured by sputum examination using Ziehl-Neelsen (ZN) or auramine-rhodamine (A/R) microscopy, in which conversion from smear positive to negative at two months is an important predictor of treatment success. These classical detection methods however cannot distinguish between live or dead mycobacteria. While the GeneXpert® has revolutionized rapid detection of resistance to the most important anti-TB drug, rifampicin (RMP), the cost of this test is still prohibitive for use on all TB cases worldwide. The WHO therefore recommends screening retreatment cases with the GeneXpert®, but in settings with a low prevalence of RMP, such as Mali, were 2% of new TB cases are estimated to have MDR-TB, new cases are not recommended to be screened by GeneXpert®. One potential improvement to microscopically following treatment success would be the use of fluorescein diacetate (FDA), an ester that needs to be cleaved by live bacteria in order to fluoresce. The objective of this study is to compare the sensitivity and specificity of FDA vital staining at 2 months (2M) as screening test for the early detection of rifampicin resistance, relative to GeneXpert®. We will conduct a prospective cohort study including 1442 new pulmonary TB patients. Sputum will be collected at baseline, 1M, 2M and 5M to test for live bacteria using FDA staining on those sputa that remain AFB positive by ZN. AFB positive sputa at 2M will also be tested for rifampicin resistance by GeneXpert. In conclusion, the proposed study will test whether FDA can serve as a low cost screening test to help identify patients who need RMP resistance testing with the GeneXpert® for early detection of drug resistant TB. Such a screening test would be a welcome tool, both in routine management of TB patients, as well as in clinical trials of new TB drugs. Early detection of MDRTB may moreover obviate the need for the more toxic category 2 treatment regimen.