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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 (IJTLD) is for clinical research and epidemiological studies on lung health, including articles on TB, TB-HIV and respiratory diseases such as COVID-19, asthma, COPD, child lung health and the hazards of tobacco and air pollution. Individuals and institutes can subscribe to the IJTLD online or in print – simply email us at [email protected] for details.

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