Abstract
Background: Identification and treatment of active and latent TB infection among household contacts is an effective strategy for TB control.
Aim: To compare the QuantiFERON-TB Gold in tube assay (QFT) to tuberculin skin testing (TST) for detecting TB infection among household contacts.
Methods: The participants were 50 immunocompetent household TB contacts. All the participants were interviewed using a questionnaire and tested by the QFT and TST. TST results were analyzed at 5 mm and 15 mm cut-off. The QFT test was interpreted following the manufacturer′s criteria. In all the subjects with a positive TST (≥15mm)/QFT, X-ray was performed.
Results: All contacts had previously been vaccinated and revaccinated with BCG and they had been screened with the TST at least once in the past. 52% (26/50) household contacts had positive TST (≥5mm) results, and 12% (6/50) had TST≥15mm. 18% (9/50) had a positive QFT finding. The comparison of TST (threshold 5 mm) and QFT results revealed a low agreement: 62% (31/50); (k=0.259). The comparison of TST (threshold 15 mm) and QFT results revealed a moderate agreement: 90% (45/50); (k=0.611). Active TB was detected in 4% (2/50) subjects.
Conclusion: Despite the intense exposition of immunocompetent household TB contacts to a highly symptomatic index case, transmission of M. tuberculosis rarely occurred. The data indicate that a previous BCG vaccination and/or TST testing could be a reason for the false positive TST results. Two tests can be used in the diagnostic algorithm of TB infection in testing household contacts. In order to apply the TST a higher cut off values (≥15 mm) should be used for positivity. The QFT assay could replace the TST in BCG vaccinated population.
- © 2012 ERS