Comparison of direct smear and concentrated sputum samples for AFB staining in Thamod and Klonghoykong Hospitals

Abstract

Tuberculosis (TB) is a chronic infectious disease and an important public health problem in Thailand. According to the report of World Health Organization 2008, approximately 90,000 new cases (142/100,000) of TB and 40,000 cases (62/100,000) with sputum positive for AFB are reported annually in Thailand. The person with AFB positive sputum is a major source of TB spreading.  Identification of the sputum positive for AFB is usually based on sputum AFB staining. Even though the test has a low sensitivity, it has high specificity and low cost, therefore it is widely used in general clinical laboratories. In this study, two hundred and forty sputum samples (120 samples each from Thamod hospitat and Klonghoykong hospital) were compared for AFB staining results between the direct smear of sputum with those using the concentrated sputum smear. The concentrated sputum was prepared by adding sputum and clorox (5.25 % sodium hypochlorite), vortexing for 5 minutes and centrifugation for 15 minutes at 3,000 rpm. The AFB staining was performed according to the Ziehl-Neelsen method. The results revealed that the concentrated sputum samples were positive for AFB staining with a statistically significant higher percentage (19 samples, 7.9 %) than that of the direct smear sputum samples (9 samples, 3.7 %) (P < 0.05).