title: QFT-Plus: a plus in variability? - Evaluation of new generation IGRA in serial testing of students with a migration background in Germany.
abstract: BACKGROUND
  Currently 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.
  
  
  METHODS
  Forty-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.
  
  
  RESULTS
  From 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).
  
  
  CONCLUSIONS
  This 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.
authors.affiliation: University Medical Center Hamburg-Eppendorf (UKE), Center of Excellence for Health Services Research in Nursing (CVcare), Hamburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Knierer
authors.affiliation: University Medical Center Hamburg-Eppendorf (UKE), Center of Excellence for Health Services Research in Nursing (CVcare), Hamburg, Germany.
authors.forename: E N
authors.initials: EN
authors.lastname: Gallegos Morales
authors.affiliation: University Medical Center Hamburg-Eppendorf (UKE), Center of Excellence for Health Services Research in Nursing (CVcare), Hamburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schablon
authors.affiliation: University Medical Center Hamburg-Eppendorf (UKE), Center of Excellence for Health Services Research in Nursing (CVcare), Hamburg, Germany ; Institute for Statutory Accident Insurance and Prevention in the Health and Welfare Services (BGW), Principles of Prevention and Rehabilitation Department (GPR), Hamburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Nienhaus
authors.affiliation: University Medical Center Hamburg-Eppendorf (UKE), Center of Excellence for Health Services Research in Nursing (CVcare), Hamburg, Germany.
authors.forename: J F
authors.initials: JF
authors.lastname: Kersten
keywords: Latent tuberculosis infection; QFT-Plus; Serial testing; Students; Variability