Table 1.

Published studies investigating the association between HCV seroconversion and sharing of drug preparation equipment

Reference	Setting	Year subjects recruited	Design, recruitment setting, sample size, testing, total follow-up time	Sample HCV prevalence (%)	Sample HCV incidence (per 100 person-years)	Multivariate results		Definition of IDU	Adjustment for confounders	Study objectives and review comments
						Syringes	Nonsyringe equipment
Hagan et al. [19]	Seattle, USA	1994–97	Prospective cohort n = 317 (of 507 eligible) Drug treatment and street-recruited Age ≥ 14 years Serologic testing Seroconversion: 53 subjects Follow-up: 12 months	–	16.7	–	RR: cooker or cotton (among syringe sharers) (past year): (not sig.; results not shown) Cooker or cotton (among syringe nonsharers) (past year): 5.9 (1.1–31.7)** Rinse water (among syringe nonsharers) (past year): 0.6 (0.1–2.7)	Injected in past year	Stratified by syringe sharing status Frequency of injecting at baseline	Objective: to assess drug equipment sharing as risk for HCV Follow-up at 1 year (questionnaire + blood at baseline and 12 months) 53 seroconversions observed, with 11 among syringe sharers Behaviours prior to cohort entry (including sharing behaviours) were not included in analysis as potential confounders Large number of eligible subjects not accounted for Information bias (errors in questionnaire data) is well discussed (esp. concerning rinse water and backloading) Discussion of impact of losses to follow-up not well supported Sharing prevalence (lifetime): Syringes: 77% Cooker or cotton: 17% (when no syringes shared)
Hahn et al. [22]	San Francisco, USA	2000–01	Prospective cohort n = 195 (of 291 eligible and 776 in cohort) Age < 30 years (median = 22) Recruitment by outreach and word of mouth seronegative at Baseline Serologic testing seroconversion: 48 subjects Follow-up: at least one extra visit after baseline	37 (of entire cohort)	25.1	HR: syringe (borrowed past 3 months from nonsex partner): 2.6 (1.2–5.6)** Syringe (borrowed past 3 months from HCV+ sex partner): 2.2 (0.8–5.7) Syringe (borrowed past 3 months from HCV− or unknown status sex partner): 0.7 (0.3–1.5)	HR: Cooker, cotton and water: 2.0 (1.0–3.8)**	Injected in past month	#Persons with whom pooled money to buy drugs (past 3 months) #Persons exchanged sex for money (past 3 months) Other variables in model	Objective: to assess risk factors for HCV seronversion from equipment sharing, backloading, injecting others and being injected and other partner characteristics Follow-up every 3 months (questionnaire + blood) Sample of young IDUs only, whose sharing behaviour may differ from older IDUs High proportion of equipment sharing drug preparation equipment defined as cooker, cotton, rinse water, injecting residue from cooker or cotton Excluded periods of no injecting risk The result for borrowing needle from HCV-positive sex partner (past 3 months) became 3.3 (1.4–7.9) when sharing nonsterile drug prep equipment was excluded from model Sharing prevalence: Syringe: 67% Cooker, cotton, water: 85%
Kapadia et al. [24]	Baltimore, Chicago, Los Angeles, New Orleans, NY, USA	1997–99	Matched case–control (5:1 matching) n = 468 (78 cases, 390 matched controls) Age = 18–30 years Community-based Serologic testing Follow-up: 12 months	36 (of entire cohort of 2198)	–	OR: Syringe (past 6 months): 1.49 (0.87–2.57)	OR: Drug prep materials (lifetime): 0.98 (0.59–1.73) Drug prep materials (past 4 months): 0.91 (0.59–1.42)	Injected in past 6 months	Stratified by syringe disinfection Others unspecified	Objective: to assess effect of bleach disinfection of syringes on risk of HCV seroconversion associated with nonsyringe materials Follow-up every 6 months (questionnaire + blood at baseline and every 6 months) With syringe disinfection, HCV risk from nonsyringe materials was significantly reduced, suggesting a strong risk of HCV with syringes Multivariate analysis of syringe sharing with adjustment or exclusion of drug prep materials was not assessed Estimate varies according to various models presented by the authors, but all consistent with 0.42 Sharing prevalence: Syringes: 27% Cooker: 41% Cotton: 33% Rinse water: 30%
Lucidarme et al. [20]	North/East, France	1999–2000	Prospective cohort n = 165 Mean age = 26.5 years Recruited from drug treatment Saliva and serologic testing Seroconversion: 16 subjects Follow-up: 12 months	–	9.0	RR: Syringe (past 3 months): 6.82 (1.25–37.26)	RR: Any syringe and drug prep equipment (container, filter and water) (past 3 months): 2.50 (0.29–21.62)	Injected once in lifetime	Gender Geographical regions Substitutive treatment Use of condoms Daily cocaine injection Duration of injecting Other variables in model	Objective: to assess incidence and risk factors for HCV from drug equipment sharing among persons who injected at least once in their lifetime Follow-up every 3 months (questionnaire + saliva) Large confidence intervals for all risk estimates leads to uncertainty of risk measure
Maher et al. [8]	New South Wales, Australia	1999–2002	Prospective cohort n = 368 Age ≥15 years (80% under 30 years) Street and treatment recruited PCR testing Follow-up: 3–6 months	17–36	30.8	HR: Syringe (past 6 months): 0.95 (0.49–1.85)	HR: Shared filter (past 6 months): 2.21 (1.15–4.23)	Injected in past 6 months	Age Gender Duration Injecting Drugs injected Recruitment location Ethnic minority status	Objective: to report on incidence of and identify risk factors for HCV seroconversion Follow-up every 3 to 6 months (questionnaire + blood at baseline and every 3–6 months) Relatively minimal losses to follow-up Equal number of subjects reporting syringe, container, filter, water sharing No multivariate results provided for container, filter, water
Miller et al. [21]	Vancouver, Canada	1996–2001	Prospective cohort n = 232 Age = 13–24 years (median = 21) Street-recruited Serologic testing Seroconversion:  37 subjects Follow-up:  unspecified	46	37.3	RR: Syringe (past 6 months): 1.13 (0.47–2.73)	Baseline unadjusted OR: cooker, cotton and/or rinse water (past 6 months): 1.0 (0.6–2.0)	Injected in past month	unspecified	Objective: to assess prevalence, incidence and risk factors for HCV among young IDUs Follow-up every 6 months (questionnaire + blood) Sample of young IDUs only, whose sharing behaviour differ from older IDUs
Rezza et al. [25]	Naples, Italy	1991–93	Nested case-control n = 106 (21 cases, 85 controls) Age = unspecified in-treatment Serologic testing Follow-up: 0.69 year (mean)	63 (of entire cohort of 713)	28.6	OR: Syringe (past 6 months): 3.7 (0.1–129.1)	OR: Nonsyringe materials (past 6 months): 1.2 (0.4–4.0)	Heroin user (not further specified)	Unspecified	Objective: to assess prevalence, incidence and risk factors for HCV and HIV seroconversion among IDUs in drug treatment Follow-up every 6 months (questionnaire + blood at baseline and one more time) Statistical power limited by small number of seroconversions and sample size Small proportion of needle sharers but not other drug paraphernalia Several of the eligible subjects were not followed-up Adjustment variables for logistic model are not provided Behaviours prior to cohort entry (including sharing behaviours) were not included in analysis as potential confounders Information bias (errors in ques tionnaire data) is well discussed
Roy et al. [23]	Quebec province and city of Ottawa, Canada	1997–2003	Retrospective cohort n = 543 Mean age = 31.8 years Street-recruited Saliva testing Follow-up:  ≥6 months	60.4	27.1	HR: Syringe borrowed (past 6 months): 1.82 (1.19–2.78)	HR: Not significant (results not shown)	Injected in past 6 months	Age injecting experience Borrowed used syringe Drug injected Prostitution District of recruitment	Objective: to report on prevalence and incidence of HCV Follow-up every 6–12 months (questionnaire + saliva) Intervals for re-assessment may be too long as cases could be re-tested at up to 12 months Mostly cocaine injecting IDUs No details about other injecting equipment considered
Thorpe et al. [18]	Chicago, USA	1997–99	Prospective cohort n = 353 (of 510 eligible in 702 in cohort) Age = 18–30 years Street-recruited Serologic testing Seroconversion: 48 subjects Follow-up: 12 months	27 (of entire cohort)	10.0	HR: Syringe (borrowed past 6 months): 2.10 (0.90–4.90)	HR: Cooker: 4.07 (1.41–11.78)** Cotton: 2.38 (1.14–4.98)** Rinse water: 2.68 (0.86–8.35) HR (adjusted for syringe sharing): Cooker: 3.54 (1.26–9.94)** Cotton: 1.98 (0.88–4.46) Rinse water: 2.29 (1.01–5.20)**	Injected in past 6 months	Education Homelessness Place of residence Frequency of injecting Cocaine injecting Syringe use Drug prep equipment use	Objective: to assess risk factors for HCV seroconversion from equipment sharing Follow-up every 6 months (questionnaire + blood) Sharing defined as injecting with previously equipment when injecting at same time as another IDU Sample of young IDUs only, whose sharing behaviour may differ from older IDUs Adjusting for syringe sharing shows effects of each of other equipment, not done in most other studies Follow-up time inconsistently reported Adjusted Sharing prevalence: Syringe: 50% Cooker: 62% Cotton: 45% Rinse Water: 54%
Villano et al. [4]	Baltimore, USA	1988–96	Matched case–control (4:1 matching) n = 142 (43 cases, 99 controls) Age ≥ 18 years Street-recruited Serologic testing Follow-up:  6.5 years median (range 2.4–7.8 years)	91.1 (of entire cohort of 1593)	6.4	OR: Syringe (past 6 months, compared with no drug use): 5.7 (2.2–14.4)** Syringe (past 6 months, no sharing of syringes: 3.0 (1.2–7.1) Similar results when adjusted for age	OR: Cookers (past 6 months compared with no drug use): 4.7 (2.0–11.1)** No sharing of cookers (past 6 months compared with no drug use): 2.9 (1.1–7.5)**	Injected in past 10 years	Age at enrolment	Objective: to assess incidence and risk factors for HCV among persons with a history of injection drug use in past 10 years Follow-up every 6 months (questionnaire + blood) Multivariate analysis only adjusted for age at enrolment and matched by time of visit, with no positive finding for syringe or container sharing Positive trend in risk estimate for sharing any equipment Crude statistical analysis (no multivariable adjustments other than for age and the matching variables) Potential confounding due to behaviours other than those occurring during the previous 6 months (including sharing behaviours) not taken into account

OR, odds ratio; HR, hazard ratio; RR, relative risk.

^**P < 0.05.