A Study on Adequacy of Sputum Samples to Detect Pulmonary Tuberculosis

SP Nepal


INTRODUCTION: Tuberculosis is one of the commonest infectious diseases in Nepal. The current guidelines
specify that pulmonary tuberculosis suspects are required to submit three sputum samples the first and the
third being spot specimens taken at the centre, and the second one an early morning sputum. The aim of this
study was to find out adequacy of two versus three sputum specimens to detect pulmonary tuberculosis.
METHOD: This analytic descriptive study was conducted among patients suspected to have pulmonary
tuberculosis over a period of six months. Three samples of sputum smear (Spot S1-Morning M-Spot S2)
were collected from a suspect from over two consecutive days. Smear microscopy with Zeihl-Neelsen (ZN)
staining was performed. Numbers of AFB were calculated and tabulated as per hundred immersion fields and
RESULT: In this study 1614 cases were included; 162 patients were smear-positive. In 122 cases acid fast
bacilli were detected in the first specimen; while the second specimen detected 40 more cases and none were
detected from the third specimen. The proportion of positives were different for S1, M and S2 (Cochran’s Q
=54.12, p<0.001). Mc Nemar test shows that morning and S2 test revealed similar distribution of positives and
negatives (p=0.72), however, morning and S1 samples showed significant difference of proportion of positives
(p<0.001). Similar results were found for S1 and S2 (p<0.001) also.
CONCLUSION: Under field conditions, 2 sputum smears are as effective as 3 smears for diagnosing smearpositive tuberculosis. If the first 2 samples were negative, the possibility of missing a third positive sample
was very low.

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