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Free Content Diagnostic accuracy of the microscopic observation drug susceptibility assay: a pilot study from India

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SETTING: The microscopic observation drug susceptibility (MODS) assay is a rapid, sensitive, low-cost liquid culture technique.

OBJECTIVE: To establish the accuracy of MODS for the detection of active pulmonary tuberculosis (TB), and to document the costs and challenges of setting up this assay in a low-income setting.

DESIGN: Prospective blinded pilot study of 200 adult TB suspects at a tertiary referral hospital in India. Reference standard included culture (Löwenstein-Jensen and automated liquid culture) and clinical diagnosis.

RESULTS: Patients were mostly male (n = 122, 61.1%) and out-patients (n = 184, 92.0%), with a mean age of 40.4 years (standard deviation 16.2). Seventeen (8.5%) were human immunodeficiency virus infected and 47 (23.5%) were reference culture-positive. Compared to reference culture, MODS was 78.9% sensitive (95%CI 62.2–90.0) and 96.7% specific (95%CI 92.0–98.8). Clinical assessment suggested that MODS was false-negative in 3/8 reference culture-positive MODS-negatives and true-positive in 4/6 reference culture-negative MODS-positives. MODS was faster than solid (P < 0.001) and liquid culture (P = 0.088), and cheaper than both.

CONCLUSION: MODS may be a good alternative to automated liquid culture, but there were several challenges in setting up the assay. Prior training and validation, setup costs and inability to rule out cross-contamination need to be taken into account before the test can be established.
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Keywords: MODS; diagnostic accuracy; tuberculosis

Document Type: Regular Paper

Affiliations: 1: Department of Microbiology, Christian Medical College, Vellore, Tamil Nadu, India 2: Department of Medicine, Christian Medical College, Vellore, Tamil Nadu, India 3: Department of Community Health, Christian Medical College, Vellore, Tamil Nadu, India 4: Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec, Canada

Publication date: 01 April 2010

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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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