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

P-C Chan1, L-Y Chang, Y-C Wu

  • 1Centers for Disease Control, Department of Health, Taipei, Taiwan.

The International Journal of Tuberculosis and Lung Disease : the Official Journal of the International Union Against Tuberculosis and Lung Disease
|November 20, 2008
PubMed

Insights

Neonatal bacille Calmette-Guérin (BCG) vaccination wanes in its effect on tuberculin skin test (TST) reactivity by age 6-7 years. New age-specific TST cut-offs are proposed to better detect latent tuberculosis infection (LTBI) in children.

Area of Science:

  • Pediatric Infectious Diseases
  • Immunology
  • Tuberculosis Research

Background:

  • Neonatal bacille Calmette-Guérin (BCG) vaccination is widely used globally.
  • The tuberculin skin test (TST) is a key tool for diagnosing tuberculosis infection.
  • BCG vaccination can affect TST reactivity, complicating the diagnosis of latent tuberculosis infection (LTBI).

Purpose of the Study:

  • To evaluate the impact of neonatal BCG vaccination on TST reactivity over time.
  • To establish optimal age-specific TST induration cut-off values for detecting LTBI in children.

Main Methods:

  • TSTs were administered to 783 children aged 3 months to 14 years with prior neonatal BCG.
  • The annual risk of LTBI was estimated using TSTs from 2504 children aged 7 years without BCG scars.
  • Goodness-of-fit analysis determined age-specific TST cut-off values.

Main Results:

  • BCG's effect on TST induration decreased with age, reaching a minimum at 6-7 years, followed by increased reactivity.
  • Optimal age-specific TST cut-off values for LTBI detection were determined: 21 mm (0-1 yr), 18 mm (2-3 yr), 13 mm (4-5 yr), and 10 mm (6-7 yr).
  • These new cut-offs showed a strong correlation with the estimated risk of LTBI in the first 7 years (r = 0.93, P < 0.001).

Conclusions:

  • The influence of neonatal BCG on TST reactivity diminishes within the first seven years of life.
  • Proposed age-specific TST cut-off values can aid in distinguishing BCG response from LTBI in young children.
Abstract

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