BackgroundCurrently available Interferon-gamma release assays (IGRAs) show a considerable variability in serial testing for latent tuberculosis infection (LTBI).This study offers first results for the new generation IGRA QuantiFERON-TB Gold Plus (QFT-Plus) introduced in 2015 in comparison with its predecessor QuantiFERON-TB Gold In-Tube (QFT-GIT) from serial testing of students with a migration background at German universities.MethodsForty-one students were selected from a previous study. All students with a positive IGRA were asked and 11 agreed to participate in this cohort study. Additionally 30 students with negative IGRA results were selected by chance. Weekly testing with QFT-Plus and QFT-GIT was performed in all individuals over a 4-week period. IGRA variability was evaluated by calculating conversion and reversion rates.ResultsFrom 41 participants a total number of 163 serial measurements were analyzed for each IGRA, leading to 122 possible IGRA changes each. QFT-Plus had four conversions and two reversions leading to a conversion rate of 4.3% (4 of 93 possible conversions, 95% CI 1.4–11.3%) and reversion rate of 6.9% (2 of 29 possible reversions, 95% CI 1.2–24.2%). QFT-GIT had 2 conversions and 1 reversion causing slightly lower rates with 2.2% conversions (2 of 91, 95% CI 0.4–8.5%) and 3.2% reversions (1 of 31, 95% CI 0.2–18.5%). Inconsistent IGRA results occurred in 4 subjects for QFT-Plus (8 stable positives, 29 stable negatives) and in 2 subjects for QFT-GIT (9 stable positives, 30 stable negatives). Agreement between the two IGRAs was 95.1% (κ = 0.89). Variance attributed to the individuals was low (QFT-Plus: ICC = 0.88).ConclusionThis study confirms occurrence of conversions and reversions for the new QFT-Plus in serial testing of a high-risk cohort in a low-incidence setting with improbable new TB contact during the study. QFT-Plus conversion and reversion rates were slightly higher than for the QFT-GIT but overall they were lower for both IGRAs than in other studies that investigated IGRA variability.Electronic supplementary materialThe online version of this article (doi:10.1186/s12995-016-0148-z) contains supplementary material, which is available to authorized users.
BackgroundThe tuberculosis (TB) incidence rate in foreign-born individuals has been increasing in Germany in recent years. Foreign students may be an important source of latent tuberculosis infection (LTBI) in low-incidence countries. In Germany, there are no guidelines for LTBI screening of foreign students. The aim of the study was to estimate LTBI prevalence and evaluate associated risk factors among foreign students in Germany. The second purpose of our study was to compare the results of the new generation of QuantiFERON-TB Gold Plus (QFT-Plus) to those of its predecessor QuantiFERON-TB Gold In-Tube (QFT-GIT).MethodsThis cross-sectional study was conducted between February 2016 and March 2016. Foreign students and young professionals attending the university and higher education institutes in Lübeck, Germany were tested with QFT-Plus and QFT-GIT. Participants filled out a questionnaire for the purpose of LTBI risk assessment and analysis. Variables associated with a positive test result were analyzed using logistic regression.ResultsOne hundred thirty four students participated in the study. The overall prevalence as regards positive results from both tests, QFT-Plus and QFT-GIT, was 9.7%, and the prevalence of positive QFT-Plus results was 8.2%. The main independent variables associated with a positive QFT-Plus result were a) being born in a high-incidence country (OR = 6.7, 95% CI: 1.3–34.3) and b) previous contact with a person with active TB (OR = 4.5, 95% CI: 1.1–18.3). Higher age (OR = 2.8, 95% CI: 0.7–11.3) and male gender (OR = 1.6, 95% CI: 0.4–6.7) showed a tendency toward positive QFT-Plus results but this was not statistically significant. Agreement between QFT-Plus and QFT-GIT results was κ = 0.85, p < 0.001.ConclusionsThe LTBI prevalence among foreign students was about 10%. We recommend implementing a policy whereby all foreign students are screened by means of a questionnaire about LTBI risk factors, so that only students with present risk factors are tested for LTBI. The agreement between the new QFT-Plus and the QFT-GIT (κ = 0.85) was good. QFT-Plus might be used in the same format as its predecessor.
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