QuantiFERON-TB Gold In-Tube® (QFT-GIT) test is used for the diagnosis of latent tuberculosis (TB) infection. Besides, QFT-GIT test could allow tracking changes in immune response among TB patients and their contacts. In high TB burden settings, reports on QFT-GIT conversions and reversions among TB patients and their contacts are limited. As part of a major project to study immune responses to TB infection, we investigated QFT-GIT test conversions and reversions among smear positive pulmonary TB patients and their household contacts over 12 months.
We followed a total of 107 HIV negative participants (33 patients and 74 contacts) in Addis Ababa. We did QFT-GIT test at baseline and 12 months later according to the manufacturer’s instructions.
At baseline, 25/33 (75.8%) of the patients and 50/74 (67.6%) of the contacts were QFT-GIT positive. At 12 months, 2 more patients (1 test negative and 1 indeterminate) became test positive. Besides, 11/24 (45.8%) test negative contacts became positive. Only one patient and one contact who were test positive at baseline became test negative 12 months later. At 12 months, the proportions of QFT-GIT test positives for patients and contacts were, therefore, 78.8% and 81.1%, respectively. Among contacts, the proportion of QFT-GIT test positives at 12 months was significantly higher compared to the corresponding proportion at baseline (McNemar, p = 0.006); similarly, the median IFN-γ response significantly increased at 12 months compared with the baseline level (Wilcoxon matched-pairs signed rank test, p = 0.01). Patients, however, had comparable median IFN-γ levels at baseline and 12 months later (p = 0.56).
Nearly half of QFT-GIT negative household contacts at baseline became positive at 12 months. This suggests that repeated screening of QFT-GIT negative contacts may be needed for epidemiological studies and interventions of latent TB in an endemic setting. A large longitudinal study may be needed to confirm our observations.
Electronic supplementary material
The online version of this article (doi:10.1186/s12879-014-0654-5) contains supplementary material, which is available to authorized users.