Table 1. Model parameters and their distributions.
Distribution ranges: Uniform: minimum, maximum; Beta: alpha, beta; Lognormal: shape, scale. DC: decompensated cirrhosis; HCC: Hepatocellular carcinoma; OAT: Opiate agonist therapy; HCNSP: High coverage needle and syringe program.
| Definition | Mean sampled value (95% CI) | Sample distribution | Unit | Reference |
|---|---|---|---|---|
| Rate of new PWID initiations | Fit to 10,000 PWID | - | Individuals per year | -- |
| Rate of infection | Fit to HCV chronic prevalence among current PWID | Per year | ||
| HCV seroprevalence among current PWID | 0.90 (0.85–0.95) | Beta (alpha= 141.74, Beta=14.48); | -- | (Fleiz-Bautista et al., 2019) |
| Proportion of infections that spontaneously clear | 0.26 (0.22–0.30) | Uniform (min=0.22, max=0.30) | -- | (Micallef, Kaldor, & Dore, 2006) |
| Sustained viral response | 0.95 (0.91–0.99) | Uniform (min=0.903, max=0.998) | -- | (Dore et al., 2016; Grebely et al., 2018) |
| Average duration of injecting until permanent cessation | 17.5 | Uniform (min=11, max=24) | Years | Weighted average assumed (15% female; 85% male) (Bórquez et al., 2018; Strathdee et al., 2008) |
| Mortality rate among PWID | 0.02 (0.016, 0.024) | Uniform (min=0.016, max=0.024) | Per year | (Bórquez et al., 2018) |
| OAT recruitment rate | Varied to fit to target proportion PWID on OAT | - | Per year | -- |
| Leaving rate from OAT | 1.5 | Uniform (min=1, max=2) | Per year | (Cornish, Macleod, Strang, Vickerman, & Hickman, 2010; Martin, Hickman, Hutchinson, Goldberg, & Vickerman, 2013; Vickerman, Martin, Turner, & Hickman, 2012) |
| HCNSP recruitment | Varied to fit to target proportion on HCNSP | - | Per year | -- |
| Leaving rate from HCNSP | Assumed to be the same as OAT (1.5) | Uniform (min=1, max=2) | Per year | Assumed same as OAT (Martin, Vickerman, et al., 2013) |
| Relative risk of HCV transmission on OAT only compared to no OAT | 0.50 (0.39, 0.64) | Lognormal (ln( 0.50), 95%CI: 0.40–0.63) | -- | (Platt et al., 2018) |
| Relative risk of HCV transmission on HCNSP only compared to no HCNSP | 0.79 (0.38, 1.60) | Lognormal (ln(0.79), 95% CI: 0.39–1.61) | -- | (Platt et al., 2018) |
| Relative risk of HCV acquisition on OAT and HCNSP compared to none | 0.23 (0.09, 0.62) | Lognormal (ln(0.24), 95% CI: 0.09–0.62) | -- | (Platt et al., 2018) |
| Relative risk of HCV transmission on involuntary CAP compared to not on involuntary CAP | 1.14 (1–1.3) | Lognormal (mean 1.14, 95% CI: 1.0–1.3) | -- | Implemented through a relative change in syringe sharing as in (Brquez et al., 2018) |
| Disease transition probabilities | ||||
| Chronic – DC | 0.016 (0.013, 0.019) | Uniform (min=0.0128, max=0.0192) | Per year | Calculated from fibrosis progression rates in (Thein, Yi, Dore, & Krahn, 2008) |
| Chronic—HCC | 0.009 (0.007, 0.01) | Uniform (min=0.0072, max=0.0108) | Per year | Calculated from fibrosis progression rates in (Thein, Yi, Dore, & Krahn, 2008) |
| DC – HCC | 0.012 (0.002, 0.04) | Beta (alpha=1.193, beta=136.107) | Per year | (Shepherd et al., 2007) |
| Excess HCV-related mortality rate from DC | 0.14 (0.11, 0.17) | Uniform (min=0.11, max=0.17) | Per year | (Shepherd et al., 2007) |
| Excess HCV-related mortality rate from HCC | 0.55 (0.31, 0.79) | Uniform (min=0.3, max=0.8) | Per year | (El-Serag et al., 2006; Shepherd et al., 2007) |