Improved Diagnosis of Pulmonary Tuberculosis using Bleach
Dr Preeti B Mindolli,
Assistant Professor, Department of Microbiology,
Shri B.M.Patil Medical College, Hospital & RC,
Bijapur-586103, Karnataka, India.
Background: The bacteriological diagnosis of tuberculosis (TB) is largely dependent on the Ziehl-Neelsen (ZN) microscopy. This method has a low sensitivity, which can be improved by the concentration of the specimen with sodium hypochlorite (NaoCl), followed by centrifugation before doing acid fast staining (AFB).
Aim: To study the improvement in the sensitivity of the sputum smear by the bleach method.
Setting and Study Design: This study was conducted in BLDEUâ€™s Shri B.M. Patil Medical College, Hospital and Research Centre, Bijapur, Karnataka, India. Eighty five patients who visited Shri B.M. Patil Medical College, Hospital and Research Centre between January 2012 to December 2012 were investigated. On spot, morning and second on spot samples were collected from each patient. Direct smears were prepared and they were stained with the hot ZN technique and the remaining samples were concentrated by using 5% NaoCl, followed by centrifugation and staining with ZN stain. The improvement in the sensitivity following the bleach method was studied.
Statistical Analysis: The Fisherâ€™s exact test was used.
Results: A total of two hundred and fifty five specimens from eighty five patients were included in this study; each patient produced three specimens. AFB was detected in twenty five direct smears and in eighty four bleach smears. A statistically significant (p < 0.001) increase in the positivity with the use of the bleach method was detected as compared to that with the use of the direct method. The ZN sensitivity, specificity, positive predictive value (PPV), and the negative predictive value (NPV) were 29%, 99%, 96% and 74% respectively with a 95% confidence interval, with the use of the 5% NaoCl method.
Conclusion: The bleach method has advantages over the direct ZN method, as it is simple and as it does not require any additional expertise beyond that which is required for the conventional direct smear microscopy. The materials and the reagents are also affordable and they are available locally.