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Free Content Age-specific cut-offs for the tuberculin skin test to detect latent tuberculosis in BCG-vaccinated children

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OBJECTIVE: To evaluate the effect of neonatal vaccination with bacille Calmette-Guérin (BCG) on tuberculin skin test (TST) reactivity over time and to define the optimal age-specific induration cut-offs to detect latent tuberculosis infection (LTBI).

DESIGN: TSTs were performed on 783 children aged 3 months to 14 years who had received neonatal BCG. The estimated annual risk of LTBI was derived from TSTs administered to 2504 children aged 7 years who lacked BCG scars. Goodness-of-fit analysis was used to determine the optimal age-specific cut-off values.

RESULTS: The effect of neonatal BCG on TST induration waned with age, reaching a nadir at age 6–7 years. This was followed by a rise in TST reactivity. The optimal age-specific TST cut-off values for the detection of LTBI was estimated to be respectively 21, 18, 13 and 10 mm at ages 0–1, 2–3, 4–5 and 6–7 years. There was a close correlation between these new cut-off values with the estimated risk of LTBI for the first 7 years of life (r = 0.93, P < 0.001).

CONCLUSIONS: The effect of neonatal BCG on TST gradually declines over the first 7 years of life. Our proposed new age-specific TST induration cut-off values could help differentiate between response to BCG and LTBI in young children.
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Keywords: BCG; infants and children; latent tuberculosis infection; tuberculin skin test

Document Type: Regular Paper

Affiliations: 1: Department of Paediatrics, National Taiwan University Hospital and College of Medicine, National Taiwan University, Taipei, Taiwan 2: Centers for Disease Control, Department of Health, Taipei, Taiwan 3: Graduate Institute of Epidemiology, National Taiwan University, Taipei, Taiwan; Genomics Research Centre, Academia Sinica, Taipei, Taiwan

Publication date: 2008-12-01

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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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