Variable | No. of observations | No. of person-years of follow-up | No. of incident cases | Rate per 100 person-years | Unadjusted HR (95% CI) | Adjusted HR† (95% CI) |
---|---|---|---|---|---|---|
Dosage of opioid agonist treatment and perceived adequacy | ||||||
Not enrolled in opioid agonist treatment | 1831 | 782.78 | 118 | 15.07 | 1.00 (Ref.) | 1.00 (Ref.) |
High dosage, perceived adequate | 663 | 274.07 | 10 | 3.65 | 0.28 (0.15–0.54) | 0.43 (0.23–0.84) |
High dosage, perceived inadequate | 214 | 86.28 | 5 | 5.80 | 0.43 (0.17–1.05) | 0.61 (0.25–1.50) |
Low dosage, perceived adequate | 510 | 207.15 | 20 | 9.65 | 0.79 (0.49–1.28) | 1.22 (0.74–2.00) |
Low dosage, perceived inadequate | 211 | 72.32 | 15 | 20.74 | 1.46 (0.85–2.50) | 1.94 (1.11–3.39) |
Age, yr‡§ | 0.83 (0.76–0.90) | – | ||||
≤ 31.6 | 856 | 430.95 | 86 | 19.96 | – | – |
> 31.6–40.4 | 859 | 375.57 | 39 | 10.38 | – | – |
> 40.4–48.2 | 856 | 326.55 | 26 | 7.96 | – | – |
> 48.2 | 858 | 289.53 | 17 | 5.87 | – | – |
Sex | ||||||
Female | 664 | 281.18 | 36 | 12.80 | 1.00 (Ref.) | 1.00 (Ref.) |
Male | 2765 | 1141.41 | 132 | 11.56 | 1.00 (0.69–1.45) | 0.74 (0.50–1.10) |
College education or higher | ||||||
No | 2472 | 1062.6 | 140 | 13.18 | 1.00 (Ref.) | – |
Yes | 957 | 359.99 | 28 | 7.78 | 0.55 (0.37–0.82) | – |
Duration of injection drug use, yr‡ | 0.79 (0.72–0.87) | 0.85 (0.77–0.94) | ||||
≤ 7.2 | 857 | 399.79 | 91 | 22.76 | – | – |
> 7.2–15.3 | 859 | 403.14 | 41 | 10.17 | – | – |
> 15.3–25.0 | 856 | 331.85 | 22 | 6.63 | – | – |
> 25.0 | 857 | 287.82 | 14 | 4.86 | – | – |
Cocaine injection, past mo | ||||||
No | 2088 | 886.91 | 52 | 5.86 | 1.00 (Ref.) | 1.00 (Ref.) |
Yes | 1341 | 535.69 | 116 | 21.65 | 3.17 (2.28–4.40) | 2.85 (2.04–3.99) |
Unstable housing, past mo | ||||||
No | 2579 | 1075.58 | 88 | 8.18 | 1.00 (Ref.) | 1.00 (Ref.) |
Yes | 850 | 347.01 | 80 | 23.05 | 2.34 (1.72–3.17) | 2.14 (1.54–2.96) |
Incarceration, past 3 or 6 mo¶ | ||||||
No | 3068 | 1245.82 | 121 | 9.71 | 1.00 (Ref.) | 1.00 (Ref.) |
Yes | 361 | 176.78 | 47 | 26.59 | 2.32 (1.65–3.27) | 1.80 (1.26–2.56) |
Previous HCV infection | ||||||
No | 2148 | 972.59 | 138 | 14.19 | 1.00 (Ref.) | 1.00 (Ref.) |
Yes | 1281 | 450 | 30 | 6.67 | 0.43 (0.29–0.64) | 0.73 (0.46–1.15) |
Follow-up wave | ||||||
2004–2011 | 912 | 551.26 | 96 | 17.41 | 1.00 (Ref.) | – |
2011–2017 | 2517 | 871.34 | 72 | 8.26 | 0.64 (0.47–0.87) | – |
Note: CI = confidence interval, HCV = hepatitis C virus, HR = hazard ratio, Ref. = reference category.
↵* Prescribed dosage was categorized as high if methadone ≥ 60 mg/d or buprenorphine ≥ 16 mg/d, and low otherwise.3,5–7
↵† Adjusted for sex (male/female), duration of injection drug use (yr), past-month cocaine injection (yes/no), past-month unstable housing (yes/no), past 3- or 6-month incarceration (yes/no), and previous HCV infection (yes/no).
↵‡ Age and duration of injection drug use were analyzed in continuous form in Cox regression models. Hazard ratios represent the effect of a 5-year increase.
↵§ Because of correlation with duration of injection drug use (Pearson correlation coefficient, r = 0.70), this variable was not entered in the multivariable Cox regression model.
↵¶ Depending on follow-up wave.