Evaluation of A Method For Detection of Viable Mycobacterium tuberculosis Using LED Microscopy, In Sputum Specimens For Follow-Up of TB Treatment
Following up the response of patients to the anti-Tuberculosis (TB) Treatment (ATT), requires basic and effective treatment monitoring tools. The commonly used monitoring tool used in peripheral TB laboratories in resourcelimited settings is microscopic observation of Acid Fast Bacilli using Ziehl- Neelsen (ZN) or Auramine OFluorescent staining. If the patient is smear positive at the third month following treatment commencement, follow up for viability of the bacillus in the sputum, is done by Mycobacterium tuberculosis (M.tb) culture and drug susceptibility testing (C & DST).
Smear positivity at the fifth month or later following treatment commencement, would signal possible treatment failure. It is significant to note that’s mear microscopy cannot distinguish between viable and dead bacilli. A large number of patients on treatment may continue to cough up dead bacilli from necrotic lung cavities, and hence be classified as “smear positive” though they respond to treatment. They are hence at risk of receiving prolonged or revised treatment regimens in settings with limited access to M. tuberculosis culture. Sputum culture can identify viable bacilli, but requires several weeks to arrive at the results, skilled laboratory staff and infrastructure.
Recent studies propose as imple method for TB treatment monitoring that can be performed at the peripheral TB laboratories with pre-existing infrastructure. It is a Point of Care (POC) technique based on the fluorescent viability marking capability of fluorescein-diacetate (FDA), as a stain for sputum smear microscopy.
The effectively of fluorescein-diacetate (FDA) staining in the detection of viable Mycobacterium tuberculosis in 567 sputum samples from follow up PTB cases was compared to growth on automated liquid culture systems (97.64% culture positivity). FDA sensitivity was moderate (97.62%, with a Confidence Interval of 95%), and specificity was (98.4%). The negative predictive value of 94.8% was encourage in ganda negative likelihood ratio of 0.2 suggested use of this method for ruling out treatment failure in low income and high burden settings.
Kanakaprasad A*, Bharathidasan, Hema Sundaram, D Farah Deeba, Nirmala AR, Abdul Azeem