Table 2:

Hazard ratios for associations between incident hepatitis C virus infection and prescribed dosage of opioid agonist treatment, categorized according to clinical guideline recommendations* and patient-perceived dosage adequacy

VariableNo. of observationsNo. of person-years of follow-upNo. of incident casesRate per 100 person-yearsUnadjusted HR (95% CI)Adjusted HR (95% CI)
Dosage of opioid agonist treatment and perceived adequacy
 Not enrolled in opioid agonist treatment1831782.7811815.071.00 (Ref.)1.00 (Ref.)
 High dosage, perceived adequate663274.07103.650.28 (0.15–0.54)0.43 (0.23–0.84)
 High dosage, perceived inadequate21486.2855.800.43 (0.17–1.05)0.61 (0.25–1.50)
 Low dosage, perceived adequate510207.15209.650.79 (0.49–1.28)1.22 (0.74–2.00)
 Low dosage, perceived inadequate21172.321520.741.46 (0.85–2.50)1.94 (1.11–3.39)
Age, yr§0.83 (0.76–0.90)
 ≤ 31.6856430.958619.96
 > 31.6–40.4859375.573910.38
 > 40.4–48.2856326.55267.96
 > 48.2858289.53175.87
Sex
 Female664281.183612.801.00 (Ref.)1.00 (Ref.)
 Male27651141.4113211.561.00 (0.69–1.45)0.74 (0.50–1.10)
College education or higher
 No24721062.614013.181.00 (Ref.)
 Yes957359.99287.780.55 (0.37–0.82)
Duration of injection drug use, yr0.79 (0.72–0.87)0.85 (0.77–0.94)
 ≤ 7.2857399.799122.76
 > 7.2–15.3859403.144110.17
 > 15.3–25.0856331.85226.63
 > 25.0857287.82144.86
Cocaine injection, past mo
 No2088886.91525.861.00 (Ref.)1.00 (Ref.)
 Yes1341535.6911621.653.17 (2.28–4.40)2.85 (2.04–3.99)
Unstable housing, past mo
 No25791075.58888.181.00 (Ref.)1.00 (Ref.)
 Yes850347.018023.052.34 (1.72–3.17)2.14 (1.54–2.96)
Incarceration, past 3 or 6 mo
 No30681245.821219.711.00 (Ref.)1.00 (Ref.)
 Yes361176.784726.592.32 (1.65–3.27)1.80 (1.26–2.56)
Previous HCV infection
 No2148972.5913814.191.00 (Ref.)1.00 (Ref.)
 Yes1281450306.670.43 (0.29–0.64)0.73 (0.46–1.15)
Follow-up wave
 2004–2011912551.269617.411.00 (Ref.)
 2011–20172517871.34728.260.64 (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.