Table 1.

Baseline characteristics of the study subjects.

Characteristic	Heroin users	Methadone users	Control group	p value*	Opioid users (heroin + methadone)	p value**
N of subjects	10	11	20		21
Age – years				<0.01a		0.12
Mean ± SD	21.7 ± 2.3	29.5 ± 5.6	28.5 ± 5.0		25.8 ± 5.8
Median	21.5	30	29		23
Range	19–24	25–40	22–35		19–40
Sex – no. (%)				0.02b		<0.01
Male	9 (90)	8 (73)	8 (40)		17 (81)
Female	1 (10)	3 (27)	12 (60)		4 (19)
Race – no. (%)				0.11		0.04
White	10 (100)	8 (73)	9 (45)		18 (86)
Black or African American	0	1 (9)	6 (30)		1 (5)
Asian	0	1 (9)	4 (20)		1 (5)
All other races	0	1 (9)	1 (5)		1 (5)
Ethnicity				0.99		0.96
Non-Hispanic/Latino	9 (90)	10 (91)	18 (90)		19 (90)
Hispanic/Latino	1 (10)	1 (9)	2 (10)		2 (10)
dPrior influenza vaccination (ever) – no. (%)	6 (60)	7 (63.6)	11 (61)e	0.98	13 (62)	0.96
dHCV infection	3 (30)f	1 (9)	0 (0)	0.03c	4 (19)	0.04

^*Three-way comparison.

^**Comparison of all opioid users vs controls.

^aAge, pairwise comparisons: heroin users vs control group p < 0.01; methadone users vs control group p = 0.60; heroin users vs methadone users p < 0.01.

^bSex, pairwise comparisons: heroin users vs control group p < 0.01; methadone users vs control group p = 0.08; heroin users vs methadone users p = 0.31.

^cHCV infection, pairwise comparisons: heroin users vs control group p < 0.01; methadone users vs control group p = 0.17; heroin users vs methadone users p = 0.22.

^dBy self report.

^eUnknown for 2 patients in control group.

^fOne subject cleared the infection.