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Free Content Reducing the string test intra-gastric downtime for detection of Mycobacterium tuberculosis

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OBJECTIVES: To explore the potential for reducing the procedural duration of the string test for the diagnosis of tuberculosis (TB) using microscopic observation drug susceptibility (MODS) culture.

METHODS: Twelve patients already diagnosed with pulmonary TB, four each with sputum smear acid-fast bacilli grade 1+, 2+ and 3+, underwent four consecutive string tests of varying intra-gastric downtime (IGDT) of 30 min, 1, 2 and 4 h. Each retrieved string was cut into three—one oesophageal and two gastric sections. Eluates from one of the gastric sections and the oesophageal section were cultured in MODS after a decontamination procedure; eluate from the other gastric section was cultured in MODS with no decontamination.

RESULTS: No significant difference was observed in the retrieval efficacy of Mycobacterium tuberculosis (P = 0.29) or time to positive MODS culture (P = 0.80) among string tests of varying IGDTs. Every patient with a sample that was positive after a 4-h IGDT also had positive culture of a 1-h IGDT sample. A pre-inoculation sample decontamination step significantly reduced culture contamination (P < 0.001).

CONCLUSION: In smear-positive patients, reducing the IGDT to 1 h did not affect the M. tuberculosis retrieval efficacy of the string test. Future evaluations in non-expectorating human immunodeficiency virus and paediatric populations should include a 1-h IGDT.

Keywords: diagnosis; string test; tuberculosis

Document Type: Regular Paper

Affiliations: 1: Harvard College, Cambridge, Massachusetts, USA 2: Hospital Nacional Dos de Mayo, Lima, Peru 3: The Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA 4: Universidad Peruana Cayetano Heredia, Lima, Peru 5: Universidad Peruana Cayetano Heredia, Lima, Peru; Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA; and Wellcome Trust Centre for Clinical Tropical Medicine, Imperial College London, London, UK

Publication date: December 1, 2008

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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