A cost effectiveness analysis of different ways of analyzing sputum for turberculosis diagnosis: direct smear microscopy, natural sedimentation and centrifugation

Master Thesis


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University of Cape Town

In Malawi, sputum smear microscopy (Ziehl-Neelsen) is a major diagnostic technique for pulmonary tuberculosis (TB). Though relatively rapid, it tends to be poorly sensitive since it requires a large number of organisms to be present in the specimen before they can be detected. Two approaches that improve sensitivity of direct smear microscopy are sputum liquefaction with chemicals such as sodium hypochlorite (household bleach) and subsequent concentration with gravity (natural) sedimentation and centrifugation. This study estimated the costs and cost-effectiveness of these techniques in processing sputum for detecting new cases of pulmonary tuberculosis in Malawi. Bleach natural sedimentation and bleach centrifugation methods were compared with direct smear microscopy. Cost and effectiveness data were collected from a randomized controlled trial from one major TB health facility. Effectiveness was determined by number of smear positive TB cases detected by each method. Cost-effectiveness was estimated from a provider's perspective in terms of cost per TB cases diagnosed and cost per smear positive TB case detected. Cost per positive TB case detected was least in natural (gravity) sedimentation (US $9.35), compared to centrifugation (US $11.48) and direct smear microscopy (US $15.93). The study findings indicate that natural sedimentation can significantly reduce cost of sputum processing. There is a strong economic case supporting the use of natural sedimentation for diagnosing tuberculosis in Malawi. In addition, bleach digests sputum making it less infectious and easy to work with thereby increasing the safety of specimens to clinicians. Therefore, introducing natural sedimentation technique would not only reduce costs but also improve safety to health workers.

Includes bibliographical references.