Agreement between direct fluorescent microscopy and Ziehl-Neelsen concentration techniques in detection of pulmonary tuberculosis in northwest Ethiopia

Abstract

Background: The sensitivity of smear microscopy for diagnosis of tuberculosis might be improved through treatment of sputum with sodium hypochlorite and application of fluorescent microscopy. This study aimed to determine the agreement between direct Fluorescent Microscopy and Ziehl-Neelsen concentration technique by their ability of detecting acid fast bacilli in resource poor settings.

Methods: A cross sectional study was conducted at Gondar University Referral Hospital, Northwest Ethiopia. Three sputum specimens were collected from consecutive TB suspects. Direct and concentrated sputum smears were air-dried, heat-fixed and stained by auramine O and Ziehl-Neelsen staining techniques respectively. The stained slides were examined for acid fast bacilli using direct Fluorescent Microscopy and Ziehl-Neelsen concentration techniques.

Results: Of 293 specimens, 4.4% and 2.4 % were AFB positive by direct fluorescent microscopy and Ziehl-Neelsen bleach concentrated techniques respectively. There was high percentage of tuberculosis positivity from early morning sputum samples (2.4%) compared to first spot (1.4%) and second spot (1.7%) sputum samples when using Ziehl-Neelsen sodium hypochlorite concentration technique. A moderate agreement was seen between the two methods (Kappa=0.484, P value<0.001).

Conclusion: Direct fluorescent microscopy has shown high positivity rate compared to Ziehl-Neelsen concentration technique. A moderate agreement was seen between the two methods. Thus, Ziehl-Neelsen bleach sedimentation technique is recommended for detection of pulmonary tuberculosis at peripheral health service level when Fluorescent Microscopy is not available

Keywords: Agreement, Direct Fluorescent Microscopy, Ziehl-Neelsen concentration, Tuberculosis, Ethiopia