Predictors of persistently positive Mycobacterium-tuberculosis-specific interferon-gamma responses in the serial testing of health care workers

Table 4 Predictors of persistent QFT-GIT positivity

	Positive Baseline and follow-up QFT-GIT
Variables	Adjusted OR* (95% CI)	p-value
Age categorized^#	5.0 (3.9-13.5)	0.001
Sex
Female	1	-
Male	1.2 (0.2-6.3)	0.80
Birth in high-burden country
No	1	-
Yes	0.2 (0.0-3.6)	0.29
BCG status	1	-
Vaccinated	0.3 (0.1-1.5)	0.15
Unknown	0.6 (0.0-9.8)	0.70
Profession
Other	1	-
Nursing	0.6 (0.1-3.4)	0.57
Physician	3.2 (0.5-22.7)	0.24
Affiliation with ID/TB Care
No	1	-
Yes	0.8 (0.1-7.8)	0.85
Family history of TB
No	1	-
Yes	1.1 (0.1-8.7)	0.96
QFT-GIT test interval per day	1.0 (0.99-1.01)	0.49
Exposure per hour^§	0.7 (0.45-1.13)	0.15
Prior TST
Negative	1	-
Positive	14.2 (1.4-143.2)	0.024
Recent TST
Negative	1	-
> 5 mm induration	12.1 (2.4-59.8)	0.002
≥ 10 mm induration	15.5 (3.1-81.3)	0.001
Baseline IFN-γ increase per 0.1 IU/ml	1.03 (1.01-1.04)	0.0006

*Variables included in final model building were age, birth in high-burden country, BCG status, recent TST result > 5 mm or ≥ 10 mm induration, and baseline IFN-γ increase per 0.1 IU/ml. ^#Compare Table 1. ^§Exposure per hour in those 134 study subjects that were recruited from contact investigations. BCG = Bacillus Calmette-Guérin; CI = confidence interval; ID = Infectious Diseases; IFN = interferon; OR = odds ratio; QFT-GIT = QuantiFERON^®-TB Gold In-Tube; TB = tuberculosis; TST = tuberculin skin test.

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