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. 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. 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.
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