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Potential role for interferon-γ release assays in tuberculosis screening in a remote Canadian community: a case
Wilson Kwong1, Thomas Krahn1, Ann Cleland1
1Department of Medicine (Kwong), University of Toronto, Toronto, Ont.; Department of Medicine (Krahn, Wobeser), Queen's University, Kingston, Ont.; Sioux Lookout First Nations Health Authority (Cleland, Gordon), Sioux Lookout, Ont.
Background:
Current Canadian guidelines suggest that neonatal Bacille Calmette-Guérin (BCG) vaccination does not result in false-positive tuberculosis (TB) skin tests, despite a growing body of evidence that interferon-γ release assays may be a more specific alternative in identifying latent tuberculosis infections in vaccinated populations. We set out to evaluate the relationship between TB skin tests and interferon-γ release assays in patients who previously received neonatal BCG vaccine.
Methods:
All children with a positive skin test at age 14 years in a remote community north of Sioux Lookout, Ontario, were considered for interferon-γ release assay testing.
Results:
Of the 11 children who underwent routine screening at 14 years of age for latent TB infection, 7 had a positive TB skin test (≥ 10 mm). All 7 of these children had received the BCG vaccine as newborns and all had a negative TB skin test during their routine screening at 4 years of age. No potential exposure to active TB could be identified. Chest radiographs were normal, and none of the children had symptoms suggestive of active TB. The 7 children underwent interferon-γ release assay testing using QuantiFERON Gold. All 7 tests were negative.
Interpretation:
With the addition of interferon-γ release assays to routine skin test screening, we provide evidence that neonatal BCG vaccination may contribute to a false-positive skin test in youth at 14 years of age. Consideration should be given to the possibility that neonatal BCG may contribute to false-positive TB skin tests.
