Abstract
BackgroundDirect sputum smear microscopy for tuberculosis (TB) lacks sensitivity for the detection of acid fast bacilli. Sputum pretreatment procedures may enhance sensitivity. We did a pilot study to compare the diagnostic accuracy and incremental yield of two short-duration (<1 hour) sputum pretreatment procedures to optimize direct smears among patients with suspected TB at a referral hospital in India.Methodology/FindingsBlinded laboratory comparison of bleach and universal sediment processing (USP) pretreated centrifuged auramine smears to direct Ziehl-Neelsen (ZN) and direct auramine smears and to solid (Loweinstein-Jensen (LJ)) and liquid (BACTEC 460) culture. 178 pulmonary and extrapulmonary TB suspects were prospectively recruited during a one year period. Thirty six (20.2%) were positive by either solid or liquid culture. Direct ZN smear detected 22 of 36 cases and direct auramine smears detected 26 of 36 cases. Bleach and USP centrifugation detected 24 cases each, providing no incremental yield beyond direct smears. When compared to combined culture, pretreated smears were not more sensitive than direct smears (66.6% vs 61.1 (ZN) or 72.2 (auramine)), and were not more specific (92.3% vs 93.0 (ZN) or 97.2 (auramine).Conclusions/SignificanceShort duration sputum pretreatment with bleach and USP centrifugation did not increase yield as compared to direct sputum smears. Further work is needed to confirm this in a larger study and also determine if longer duration pre-treatment might be effective in optimizing smear microscopy for TB.
Highlights
Direct Ziehl-Neelsen (ZN) sputum smear microscopy for the detection of acid fast bacilli (AFB) remains the most important diagnostic test for tuberculosis (TB) in high burden countries
This study evaluated the improvement in sensitivity, as well as incremental yield, of two combinations of short duration chemical and physical pretreatment procedures for smear microscopy in a large referral hospital in south India
Our preliminary study evaluated two short-duration sputum pretreatment methods among pulmonary TB suspects in a large referral centre in India
Summary
Direct Ziehl-Neelsen (ZN) sputum smear microscopy for the detection of acid fast bacilli (AFB) remains the most important diagnostic test for tuberculosis (TB) in high burden countries. Specific, and appropriate for laboratories with minimal infrastructure, sputum microscopy failed to detect 56% of the estimated global burden of new TB cases in 2006.[1] The proportion of missed cases may be higher among HIV infected patients, who are often smear negative despite multiple smears.[2] The analytical sensitivity of direct sputum smear microscopy is approximately 10,000 bacilli per millilitre of sputum, much less than culture methods.[3] The Global Plan to Stop TB recognizes the limitations of sputum smear microscopy and mandates further research into the optimization of this technique.[4,5]. Direct sputum smear microscopy for tuberculosis (TB) lacks sensitivity for the detection of acid fast bacilli. We did a pilot study to compare the diagnostic accuracy and incremental yield of two short-duration (,1 hour) sputum pretreatment procedures to optimize direct smears among patients with suspected TB at a referral hospital in India
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