Objective: Assays based on interferon γ (IFNγ) are an exciting new development for screening for latent tuberculosis infection (LTBI) in adults, but there are limited data on their effectiveness in children. Nevertheless new National Institute for Health and Clinical Excellence (NICE) guidelines recommend their use when screening paediatric tuberculosis (TB) contacts. We evaluated the potential effect of the new NICE guidelines on current paediatric practice.
Design: Children screened for TB who had had an IFNγ assay performed (QuantiFERON-TB Gold (QFG)) were included. Actual outcomes from existing guidelines were compared with those that would have been obtained using NICE guidelines.
Results: QFG assays were performed on 120 children, 103 as part of TB contact tracing. Six of the 120 (5%) were QFG positive, and seven of the 120 (6%) were indeterminate. Where both Mantoux and QFG results were available, these agreed in 62/104 (60%) of cases. QFG tests were more likely to correlate with a negative Mantoux (98% agreement) than with a positive Mantoux (11% agreement). Management outcomes differed for 23/103 children seen as part of TB contact tracing. Only one (1%) of these had an indeterminate QFG result. 17 (85%) fewer children would have been given LTBI treatment (chemoprophylaxis) and two (2%) children with possible TB would not have been identified using NICE guidelines.
Conclusion: New NICE guidelines for the use of IFNγ-based tests for TB screening will reduce the number of children treated for presumed LTBI. Long-term prospective studies are needed to determine the number of children with positive Mantoux tests but negative IFNγ results who are not given LTBI treatment yet later develop TB.
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Competing interests: None.