Use of light-emitting diode fluorescence microscopy to detect acid-fast bacilli in sputum as proficient alternative tool in the diagnosis of pulmonary tuberculosis in countries with limited resource settings.

Abstract

Despite recent advances in the development of more sensitive technologies for the diagnosis of tuberculosis (TB), in resource-limited settings, the diagnosis continues to rely on sputum smear microscopy. This is because smear microscopy is simple, cost-efficient and the most accessible tool for the diagnosis of TB. Our study evaluated the performance of light-emitting diode fluorescence microscopy (LED-FM) using auramine/rhodamine (auramine) and the fluorescein di-acetate (FDA) vital stain in the diagnostic of pulmonary TB in Bamako, Mali. Sputum smear microscopy was conducted using the FDA and auramine/rhodamine staining procedures on fresh samples using LED-FM to evaluate the Mycobacterium TB (MTB) metabolic activity and to predict contagiousness. Mycobacterial culture assay was utilized as a gold standard method. Out of 1401 TB suspected patients, 1354 (96.65%) were retrieved from database, which were MTB complex culture positive, and 47 (3.40%) were culture negative (no mycobacterial growth observed). Out of the 1354 included patients, 1343 (95.86%), were acid-fast bacillus (AFB) positive after direct FDA staining, 1352 (96.50%) AFB positive after direct Auramine, and 1354 (96.65%) AFB positive with indirect auramine after digestion and centrifugation. Overall, the FDA staining method has a sensitivity of 98.82%, while the sensitivity of Auramine with direct observation was 99.48%, and 99.56% with the indirect examination. This study showed that, using fresh sputum both auramine/rhodamine and FDA are highly sensitive methods in diagnosing pulmonary TB and could be easily used in countries with limited resource settings.