Tuberculin sensitivity among children vaccinated with BCG under universal immunization programme.

Area of Science:

• Public Health
• Infectious Diseases
• Immunology

Background:

• Bacille Calmette-Guérin (BCG) vaccination is widely used to prevent tuberculosis (TB).
• Tuberculin skin testing (TST) is a key tool for TB diagnosis, but BCG vaccination can cause false-positive results.
• Accurate interpretation of TST results in BCG-vaccinated populations is crucial for effective TB control.

Purpose of the Study:

• To evaluate the impact of BCG vaccination on tuberculin skin test (TST) reactions in Indian children.
• To determine the upper limit of TST reactions attributable to BCG vaccination.
• To guide the interpretation of TST results in BCG-vaccinated children.

Main Methods:

• A large-scale tuberculin survey was conducted in rural India.
• Participants included 45,988 children with BCG scars and 54,227 children without BCG scars, aged 1-9 years.
• TST reactions were measured and analyzed based on BCG vaccination status.

Main Results:

• Most BCG-vaccinated children (45-60%) showed TST reactions < 5 mm, and 70-80% showed reactions < 10 mm.
• TST reactions between 5-19 mm in BCG-vaccinated children may be influenced by the vaccine.
• TST reactions ≥ 20 mm were considered indicative of tuberculous infection, irrespective of BCG vaccination status.

Conclusions:

• BCG vaccination generally does not interfere with the interpretation of TST results in the majority of children (TST reaction < 10 mm).
• Careful interpretation is needed for TST reactions between 10-19 mm in BCG-vaccinated children.
• A TST reaction of 19 mm appears to be the upper limit for BCG-induced tuberculin sensitivity.