Interpretation of the PPD skin test in BCG-vaccinated children

Area of Science:

• Immunology
• Infectious Diseases
• Pediatrics

Background:

• The bacille Calmette-Guérin (BCG) vaccine is widely used for tuberculosis prevention.
• Tuberculin skin testing, specifically using purified protein derivative (PPD), is a common method to assess cell-mediated immunity to Mycobacterium tuberculosis.
• Evaluating the efficacy and interpretation of PPD skin tests post-BCG vaccination in children is crucial for accurate tuberculosis diagnosis.

Purpose of the Study:

• To evaluate the interpretability of the purified protein derivative (PPD) skin test at different time points after bacille Calmette-Guérin (BCG) vaccination in children.
• To compare the PPD test results in children vaccinated with BCG at birth versus those vaccinated at age six years.

Main Methods:

• Administered 5 tuberculin units (TU) of PPD stabilized with polysorbate (Tween) 80.
• Conducted skin testing 3 months and 1 year post-BCG immunization.
• Studied two groups of children: those vaccinated at birth and those vaccinated at age 6 years.

Main Results:

• PPD skin test interpretation is possible in children aged 1 year and older vaccinated with BCG at birth.
• A PPD induration diameter exceeding 10-12 mm in BCG-vaccinated children (at birth) suggests supervening infection (Mycobacterium tuberculosis or atypical mycobacteria), not BCG reaction.
• Interpreting PPD skin tests in children vaccinated with BCG at age 6 years proved extremely difficult.

Conclusions:

• The PPD skin test can be a useful diagnostic tool in children over one year old previously vaccinated with BCG at birth.
• The timing and age of BCG vaccination significantly impact the interpretability of subsequent PPD skin tests.
• Further research may be needed to establish reliable interpretation guidelines for PPD tests in children vaccinated later in life.