Evaluation of Fluorescein Diacetate Viability Staining during Treatment Follow-up Examinations of Smear Positive Pulmonary Tuberculosis Patients

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BACKGROUND: Assessment of treatment response to pulmonary tuberculosis (TB) is currently done by follow-up cultures since smear microscopy cannot distinguish viable from nonviable bacilli. This delays the therapeutic decision and increases the work load on the TB laboratories. This study evaluated the utility of fluorescein diacetate (FDA) viability staining against culture as a modality to assess treatment response in patients receiving anti tubercular treatment. METHODS: In a cross-sectional study conducted for 2 years at a tertiary care hospital, around 110 follow-up sputum samples from patients with initial smear positivity were collected. After being processed for light-emitting diode fluorescence (FL) microscopy and liquid culture by MGIT 960, the samples were subjected to FDA viability staining as an additional step. FDA staining and FL microscopy results were compared to culture to determine its diagnostic accuracy in predicting bacterial viability. RESULTS: The positivity rates for FL microscopy, FDA microscopy, and culture were 17%, 10%, and 8.18%, respectively. Culture results correlated with FL microscopy in 83.6% of cases and with FDA staining in 94.5%. FDA staining outperformed FL microscopy in terms of sensitivity, specificity, positive predictive value (PPV), and NPV, with values of 77.7%, 96.04%, 63.6%, and 97.9%, respectively. Among FL microscopy positive samples, FDA staining demonstrated 100% sensitivity and NPV, but poor specificity and PPV (57.14% and 45.45%, respectively) owing to false positive results in some cases. CONCLUSION: FDA viability staining proved to be a better predictor of bacteriological clearance during follow-up examinations of patients on antitubercular therapy and may be explored in future research.

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