Application of Bleach Method to Improve Smear Microscopy for the Diagnosis of Pulmonary and Extrapulmonary Tuberculosis

ABSTRACT

Background: The microbiological diagnosis of pulmonary TB by direct sputum smear microscopy plays a key role in routine diagnosis of TB and treatment follow up in Tuberculosis Control Programs in India. Direct smear preparation of clinical samples is hazardous for technicians working in centers without a bio-safety hood. Studies have shown that sensitivity of smear microscopy can be improved if the sputum sample is liquefied with one or more chemical reagents and then concentrated by centrifugation or sedimentation before acid fast staining. The present study aimed to quantify the gain in positivity of microscopic detection and to test its implementation in a peripheral laboratory participating. Methods: This is a prospective observational study were conducted in the Department of Microbiology, Kamineni Institute of Medical Sciences, Narketpalli, Nalgonda, Telangana, India. A total of 100 patients, of all age groups and sex, presenting to the OPD for the first time, with clinical suspicion of pulmonary or extrapulmonary TB was included in the study. All the demographic details of the patients were noted and consent was taken from patients. Salivary samples were immediately removed and a new sample was requested. The time between sputum collection and analysis was recorded. Results: In present study the 100 patients enrolled, the male/female ratio was 1.32, the mean age was 57 years (range 10–85), and 92% of patients were sampled for TB case detection. Only one patient had known HIV infection. Overall, AFB were detected on 44 smears prepared by the direct method (12.3%) and 55 smears prepared by the bleach method (16.0%), a statistically significant difference (P = 0.0006), giving an increase in positivity. The semi-quantitative results highlighted a significant gain in positivity (P < 0.001) with the bleach method. Conclusion: Our study, conducted in a population with a low prevalence of HIV/AIDS, confirms the benefits of the bleach method for the microscopic case detection of pulmonary TB. This rustic, simple and inexpensive method could easily be integrated into the routine of a peripheral laboratory after a short training period and strengthening of quality assurance.