Table 1. Equation 1 parameters, values and sources.

Transmission probability was calculated based on Equation 1 (Eq. 1). The parameters VL, s, ρ, and q used in Eq. 1 are described together with values and their ranges. Sources are identified; either calculated in this study, taken from previously published data or estimated from experts familiar with practices employed by injecting drug users. IU, international units; HCV, hepatitis C virus; HDSS, high dead space syringe; LDSS, low dead space syringe; IQR, interquartile range (Q1-Q3).

Parameter	Description [units]	Value [Range]	Scenario	Source
n	Number [#] of transferred HCV RNA IUs by contaminated syringe	VL·ρ·s		Calculated as described in text and in Fig. 1
VL	Donor’s viral load in blood [RNA IU / mL]	Variable [0 to 6 log10 IU/mL]	Experimental	Values input for testing (Fig. 4 and Table 1)
		Time-dependent: 3 primary acute-phase viral kinetic patterns	Self-limiting, transient, chronic outcome (Figs. 5A, B and C)	InC3 Study (17–20)
		Time-dependent: 3 reinfection viral kinetic patterns	Self-limiting (Low and high titer) and chronic outcome (Figs. 5D, E and F)
s	Donor blood as a fraction of the mixture with illicit drugs [%]	25% [5%−50%]		Expert view
ρ	HCV RNA carry-over	0.6% [0.02 to 2.6%]	LDSS	Estimated in the current study (Fig. 2)
		3.1% [1.4 to 7.2%]	HDSS
		0.12% [0.003 to 0.8%]	LDSS + rinse
		0.38% [0.03 to 0.77%]	HDSS + rinse
q	Ratio of infectious doses to HCV RNA IU	17% [IQR 7–33%]		Table S2 based on published studies (8, 9, 11, 21, 22)