[Interpreting 'equivocal' results obtained from the QuantiFERON-TB Gold In-Tube test in contact investigations]

In this study, we demonstrate the interpretation of "equivocal" results by the QuantiFERON"-TB Gold In-Tube (QFT-GIT) test in contact investigations.The participants of the contact examinations were assessed by the QFT-GIT test after 2 to 4 months from the last contact with smear-positive tuberculosis patients. The study was conducted between April 2011 and March 2012. We enrolled 79 contact participants whose QFT-GIT tests produced equivocal results.The average age of the enrolled contacts was 35.9 years and the average interval from the last contact to the first QFT-GIT test was 85.4 days (range 62-118 days). The second QFT-GIT test produced negative results in 42 (53%) participants, equivocal results in 28 (35%), and positive results in 9 (11%). These 9 positive contacts belonged to the group of contacts with an index case whose QFT-GIT positive rate was more than 15%. The contacts belonging to groups with a QFT positive rate higher than 15% in the initial test had significantly higher QFT positive rates in the follow-up test than those belonging to groups with lower initial QFT positive rates (p=0.011).After retesting contacts with initially equivocal QFT results, 65% demonstrated either negative or positive results. If a contact's second QFT-GIT test is positive, it is highly probable that he/she is infected with tuberculosis and adequate treatment for latent TB infection is indicated. Thus far, no guidelines have been established for the management of contacts with equivocal results by the QFT-GIT test; therefore, further investigations and discussions are mandatory.