Fluorescein diacetate vital staining for detecting viability of acid-fast bacilli in patients on antituberculosis treatment

Objective: To determine the performance of FDA vital staining method in detecting viability of acid fast bacilli in comparison with culture and also its correlation with conventional drug susceptibility testing results for isoniazid and rifampicin. Design: The study was conducted from Jan 2014 to June 2015. Sputum samples of patients taking either Cat I or Cat II anti-TB treatment were tested by Ziehl Neelsen and FDA staining, culture and susceptibility to rifampicin and isoniazid at the end of intensive phase. Results: Of the 100 ZN positive specimens, 74 were FDA positive of which 70 were reported positive by both the readers. All specimens having higher grades (2+ and 3+) by ZN were positive by FDA staining. 87.88% of 1+ and 45% of scanty smears were positive by FDA staining. MTB was isolated in 75 specimens of which 72 were positive by FDA. Two culture negative specimens were FDA positive. FDA staining had sensitivity and specificity of 96% and 92% respectively. 70.66% of the total culture isolates were MDRTB strains. 2.66% strains demonstrated monoresistance to each of INH and rifampicin. Conclusion: FDA microscopy can be used as a simple and rapid TB treatment monitoring tool in resource limited settings to identify those patients requiring immediate culture and DST test.