Phenol-ammonium sulfate microscopy method for diagnosis of pulmonary tuberculosis

Abstract

Background: Collection and processing of sputum samples for the detection of acid fast bacilli (AFB) is hazardous for health-workers in developing countries with limited facilities. The phenol ammonium sulfate (PhAS) method involves smear microscopy and Ziehl-Neelson (ZN) staining of precipitates/ floccules formed in sputum samples when PhAS is added. The present study has been designed to assess the performance and safety of this method. Materials and methods: The study was conducted from January 2011 to March 2011 at the Department of Microbiology, Lala Ram Sarup Institute of Tuberculosis and Respiratory Diseases, New Delhi. A total of 1038 sputum samples were subjected to ZN staining before and after treatment with PhAS. The smear microscopy results of the PhAS treated and untreated samples were compared. In addition, 200 representative samples were inoculated after processing by petroff's method directly for culture and after treatment with PhAS. Result: The sensitivity, specificity, positive predictive value and negative predictive value of the PhAS solution treated ZN smear microscopy method were found to be 98.8%, 88.5%, 98.0% and 92.7% respectively in comparison with direct smear microscopy. The overall correlation between the two methods was found to be 97.3%. None of the PhAS treated samples grew Mycobacterium tuberculosis on culture. Conclusion: Sputum microscopy with PhAS solution is a safe, reliable and inexpensive alternative for direct microscopy. This method can be conveniently applied for usage in microscopy centers with limited bio-safety facilities.

Keywords

• Acid-fast
• Microscopy
• Phenol
• Ammonium-sulphate
• Sputum
• Mycobacterium