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

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.

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: 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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