Laban Habokwesiga - Department of Biotechnical and Diagnostic Sciences, School of Biosecurity, Biotechnical and Laboratory Sciences, Makerere University, Kampala, Uganda.
Nathan Lubowa - Department of Biotechnical and Diagnostic Sciences, College of Veterinary Medicine, Animal Resources and Biosecurity, Makerere University, Kampala, Uganda.

Background: Tuberculosis remains a major public health problem worldwide. Direct Ziehl Nelseen (ZN) is the conventional Laboratory method for diagnosis of TB. However, there are higher chances of missing TB positive cases due to insufficient sensitivity. This would eventually lead to TB transmission and hence mortality. Objective:  To determine sensitivity and specificity of ZN diagnostic technique on concentrated and unconcentrated sputum samples as well as to assess how clinical, socio-demographic, and sample variables affect concentrated sputum ZN positivity. Method and Materials: This cross-sectional investigation was carried out in Mulago Hospital, covering adult TB presumptive patients. Sputum samples from ۱۱۴ patients were collected and processed by both NaOCl concentration and direct ZN diagnostic techniques. Sensitivity and specificity were calculated and tabulated. Prediction of ZN positivity was assessed using Logistic regression analysis. Results:  Out of the total ۱۱۴ samples, ۸۲ (۷۱.۹%) were positive by GeneXpert test (the gold standard), whereas by NaOCl concentration method ۷۹ samples (۶۹.۳%) were found positive but with direct ZN method ۶۵ samples (۵۷.۰%) were found positive, thus an increase of ۱۴ samples (۱۲.۳%) in positivity was noted when used NaOCl concentration method which is highly significant with ρ<۰.۰۵ (χ۲ =۹۵.۳۸). NaOCl concentration method got a higher sensitivity than direct sputum smear with ۹۷.۵% and ۸۰.۲% respectively. The specificities were almost the same with NaOCl method ۹۳.۹% and direct sputum smear with ۹۰.۹%. NaOCl concentration method had a PPV of ۰.۹۸ and NPV of ۰.۹۴ while direct sputum smear had PPV of ۰.۹۵ and NPV of ۰.۶۵. Conclusion: NaOCl concentration method was found to be more sensitive than direct ZN though the specificity was almost the same. Clinical, socio-demographic and sample factors’ effect on ZN positivity was not statistically significant (ρ value=۰.۷۹۶). NaOCl concentration method should be adopted for effective diagnosis of pulmonary TB.

Fluorescent microscopy, Mucoid sputum, Muco-purulent sputum, Purulent sputum.