Table 2

Univariate and multivariable time-dependent Cox regression results for incident TB (n=252) by interferon-γ (IFN-γ) level, age group, country of origin and medical risk factors (n=48 121) QuantiFERON TB Gold (QFT) results for 44 006 individuals

Covariate	Tests (n)	TB eventsa*	Yearsb†	c HR	a HR	P values	95% CI
IFN-γ level (IU/mL)c‡						<0.001§
Negative (<0.35)	37 253	29	1 33 647	1 (ref)	1 (ref)
Low positive (0.35 to<1.0)	2488	16	6995	10.7	8.8	<0.001	4.66 to 16.50
Medium positive (1.0 to<4.0)	2971	50	9087	25.1	19.2	<0.001	11.62 to 31.60
High positive (≥4.0)	5373	157	16 233	43.0	31.3	<0.001	19.82 to 49.53
Origin
Foreign-born	21 016	224	71 983	1 (ref)	1 (ref)
Norwegian-born	27 105	28	94 045	0.09	0.6	0.015	0.36 to 0.90
Age group (years)
>35	25 381	83	88 163	1 (ref)	1 (ref)
<35	22 740	169	77 865	2.3	1.6	0.001	1.23 to 2.14
Any medical risk factore¶
None	29 674	221	1 04 063	1 (ref)	1 (ref)
At least one	18 447	31	61 964	0.3	1.3	0.234	0.84 to 2.03

*Diagnosed >3 months after QFT testing.
†Sum of person-years of follow-up after QFT testing.
‡Denominators vary due to missing IFN-γ levels.
§Likelihood ratio test for the whole IFN-γ level variable.
¶Based on ICD-10/NCMP codes for data from the Norwegian Patient Registry and ATC codes for data from the Norwegian Prescription Database.
aHR, adjusted HR; cHR, crude HR; ICD-10, International Classification of Diseases, 10th revision; NCMP, Norwegian Classification of Medical Procedures.