To TST or not to TST: is tuberculin skin testing necessary before BCG immunisation in children?

Bacille Calmette-Guérin (BCG) vaccine is one of the most commonly administered vaccines worldwide. In countries with high tuberculosis (TB) prevalence, it is generally given shortly after birth. In a number of low TB prevalence countries, BCG is used as a travel vaccine, typically given to children outside the neonatal period prior to visiting regions where TB is common. In this setting, it is recommended that latent TB infection (LTBI) resulting from prior exposure to Mycobacterium tuberculosis is excluded by a tuberculin skin test (TST) before BCG immunisation. This is to avoid the risk of an accelerated local reaction that is more common in individuals who have LTBI. In addition, BCG immunisation in individuals with LTBI is unnecessary, as it does not provide protection against progression to active TB disease. We review and discuss current international guidelines and recommendations on the need to screen children for LTBI prior to BCG immunisation. Guidelines vary significantly regarding age-related cut-offs and additional selection criteria. This variation primarily reflects the lack of evidence on which to base recommendations. We suggest an alternative strategy using a risk assessment questionnaire to identify children who should have a TST before BCG immunisation. This targeted approach will reduce the number of children unnecessarily screened, whilst allowing the identification of those with LTBI, who need further evaluation and treatment.