Abstract
Objectives: Evaluate how continuous Interferon gamma response varies across and within individuals over time in nursing students at a tertiary care hospital in Southern India upon annual screening for LTBI using QFT-GIT.
Methods: Students were approached to participate in a longitudinal study. In addition to history, clinical log books provided detailed information on potential TB exposure prior to baseline, and between annual testing. Students underwent QFT-GIT testing in 2008, 2009 and 2010.
Results: 125 nursing students completed QFT testing at 2-3 points for a total of 311 observations. We present a trajectory plot of continuous IFN-gamma across time for each participant.
There exists a high degree of correlation among observations from the same individual (ICC=0.55). To account for the correlation within individuals over time, we used linear mixed models to estimate a subject specific random effects model. We found IFN-gamma results to be negatively associated with successive visits (-0.09) suggesting responses may decrease over time within individuals, independant of exposure, although this effect was small and not statistically significant. We also identified a small random effect for student (variance = 1.76) after accounting for known LTBI risk factors and TB exposure, suggesting there may be unknown factors contributing to differences in baseline IFN-gamma response across students.
- © 2011 ERS
