Abstract
BackgroundImmigrants from countries with high incidence of tuberculosis (TB) are usually offered screening when they arrive to low incidence countries. The tuberculin skin test (TST) is often used. The interferon gamma release assays (IGRAs) are more specific and not affected by BCG vaccination. The aims of this study were 1. To see if there if there is a correlation between a positive IGRA (QFT) and presence of a BCG scar in children with TST ≥10 mm, 2. To compare the TST diameter with QFT result, 3. To see if chest X-ray can be omitted in QFT negative children despite TST ≥10 mm.Methods762 healthy children/adolescents (median age 14 years) arriving to Gothenburg and surroundings with TST ≥10 mm were tested with QFT.ResultsA total of 163/492 (33 %) children with BCG scar had positive QFT, whereas 205/270 (76 %) without BCG scar had positive QFT (p < 0.0001). The median TST was 12 mm in QFT negative and 18 mm in QFT positive children (p < 0.0001) but with considerable overlap. Median TST was the same (12 mm) in QFT negative children with and without BCG scar. Among the QFT positive children 25/368 had chest X-ray changes compared to 2/393 among the QFT negative children (p < 0.0007).ConclusionsPrevious BCG vaccination had an effect on the TST diameter so an IGRA is recommended to diagnose latent TB. Using only TST for screening of latent TB would lead to overdiagnosis. The TST diameter was larger in QFT positive than in QFT negative children but could not predict QFT in the individual patient. Chest X ray contributes little to the diagnosis of TB in QFT negative children but can not be omitted because of late seroconversion of QFT in some patients.Trial registrationNot applicable.
Highlights
Immigrants from countries with high incidence of tuberculosis (TB) are usually offered screening when they arrive to low incidence countries
From 2007 children coming to the Gothenburg area with TST ≥10 mm, irrespective if a Bacillus calmette guérin (BCG) scar was visible or not, were referred to clinics specialising in TB where Quantiferon was assayed
The finding that a higher proportion of children with scar had negative QFT than children without scar (67 % verus 24 %) speaks in favour of the possibility that BCG vaccination resulting in a scar influences TST while the finding of the same TST diameter in QFT negative children with and without scar speaks against an effect of BCG scar on TST (12 mm in both groups)
Summary
Immigrants from countries with high incidence of tuberculosis (TB) are usually offered screening when they arrive to low incidence countries. The tuberculin skin test (TST) is often used. To see if there if there is a correlation between a positive IGRA (QFT) and presence of a BCG scar in children with TST ≥10 mm, 2. To see if chest X-ray can be omitted in QFT negative children despite TST ≥10 mm. Immigrants from countries with high incidence of tuberculosis (TB) are offered medical examination and screening for TB and other infectious diseases when they arrive to Sweden. The screening for TB consisted until recently of physical examination and a tuberculin skin test (TST). From 2007 children coming to the Gothenburg area with TST ≥10 mm, irrespective if a BCG scar was visible or not, were referred to clinics specialising in TB where Quantiferon was assayed. The TST limit of 10 mm follows the recommendations of the National Board of Health and Welfare
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