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Background: Direct smear microscopy is still the primary tuberculosis (TB) diagnostic tool in developing countries despite its poor sensitivity. Improving its performance could enhance TB case detection rates.
Objective: The present study is therefore aimed at determining the value of bleach treated and direct sputum smears in combination with LuminTM LED based fluorescent microscopy (FM) to diagnose pulmonary TB (pTB) in Kilimanjaro region.
Methods: A total of 267 sputum samples were collected from pTB suspected cases consecutively attending at Mawenzi Hospital laboratory from December 2009 to February 2010. On each specimen conventional direct ZN, direct auramine, bleach centrifugation and bleach short-sedimentation auramine smears were prepared. Lumin-LED fluorescent and light microscopes were used to examine auramine and ZN stained smears, respectively. All slides were evaluated by two readers independently.
Results: Of the 267 sputum samples included in this study, 77 (29%), 62 (23%), 72 (27%) and 50 (19%) of the smears were AFB positive by bleach centrifugation, bleach short-sedimentation, direct auramine and conventional ZN methods, respectively. The highest yield was observed from bleach centrifugation with 27 (21%) extra positives over conventional ZN microscopy (p<0.0001) but was not superior to direct auramine method (p=0.46), which provided 22 (18%) more positives than conventional ZN method (p<0.0001). Twelve (11%) more positives were detected by bleach short-sedimentation over conventional ZN (p=0.03). Inter-reader agreement was high (Kappa >0.80) in all the methods evaluated. The average time required to read a slide using Lumin LED based FM was 1.5 minutes while conventional ZN method required 4 minutes (p< 0.0001).
Conclusion: Our analysis revealed that Lumin LED based FM with direct smear preparation is more effective than other smear microscopy methods in this setting. The reduced time spent to examine a slide would make this technology realistic for low human resourced busy laboratories. Further study is therefore warranted to confirm this finding under routine conditions. |
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