Comparison of Ziehl–Neelsen light microscopy and fluorescent (light-emitting diode) microscopy with solid culture for the diagnosis of tuberculosis with special reference to extrapulmonary cases

Abstract

Introduction Owing to the HIV pandemic, partially fuelled by breakdown of infrastructure and poverty, the increase in tuberculosis (TB) cases has reached unmanageable levels in the developing countries. Smear microscopy is still the main diagnostic modality. Efficient and prompt case detection followed by adequate treatment has drastically reduced TB transmission. Hence, an effort was made to compare Auramine-O (AO) and Ziehl–Neelsen (ZN) staining methods for demonstration of acid-fast bacilli with solid culture on Lowenstein–Jenson medium as a reference standard. Patients and methods A total of 100 sputum and 50 extrapulmonary samples from patients clinically suspected of TB were included. Smears were stained by ZN and AO method separately. All the samples were processed as per Revised National Tuberculosis Control Program (RNTCP) guidelines of India and inoculated on Lowenstein–Jenson medium. Mycobacterium tuberculosis was identified by their growth characteristics, nitrate reduction test, and susceptibility to para-nitrobenzoic acid. Results Of 150 samples, 27 (18%), 37 (24.67%), and 38 (25.33%) were positive by ZN stain, AO stain, and culture, respectively. Of 50 extrapulmonary samples, none were positive by ZN stain, four (8%) were positive by AO stain, and two (4%) by culture. AO method detected additional 8% of extrapulmonary TB cases which were missed by ZN and also detected more number of paucibacillary cases. Sensitivity and specificity of ZN were 71.05 and 100%, respectively. Sensitivity and specificity of AO were 86.84 and 96.43%, respectively. Conclusion The higher sensitivity and diagnostic accuracy of AO method indicate that the light-emitting diode fluorescent microscopy can be efficiently implemented in resource-limited settings with a high burden of TB.

Keywords

• auramine-o stain
• fluorescent microscopy
• light-emitting diode
• tuberculosis
• ziehl–neelsen stain