Authors: Bae, W.H.1; Salas, A.2; Brady, M.F.3; Coronel, J.4; Colombo, C.G.L.4; Castro, B.4; Gilman, R.H.5; Moore, D.A.J.5
Source: The International Journal of Tuberculosis and Lung Disease, Volume 12, Number 12, December 2008 , pp. 1436-1440(5)
Publisher: International Union Against Tuberculosis and Lung Disease
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: tuberculosis; diagnosis; string test
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