Table 1 Descriptive studies of treatment utilization/entry

Altice, 2003, US (New Haven) [31]

Cohort study

HIV-positive PWID at an SSP (N = 13)

(a) Viral load and CD4 count; (b) entry into SUD treatment

(a) 85% had undetectable viral load at 6 months, 77% at 9 months and 54% at 12 months. Net increase in CD4 count = 150 cells/ml

(b) 69% entered SUD treatment: 8 methadone,1 long-term residential program

Carvell, 1990, UK (London) [23]

Cross-sectional

SSP participants (N = 133)

Characteristics of SSP participants receiving and completing referrals to SUD treatment and medical services (n = 93) vs. not receiving referrals (n = 43)

Receiving and completing referrals vs. non-referred:

mean age 17.3 vs. 18.9 (p < 0.05)

age at 1st time injecting: 17.6 vs. 19.4 (p < 0.03)

age daily injecting began: 18.8 vs. 21.2 (p < 0.003)

Deering, 2011, Canada (Vancouver) [30]

Cohort study

Female sex workers (N = 242)

(a) SUD treatment service utilization

(b) Association between using peer-led mobile outreach program (including syringe services) (n = 97) vs. not using (n = 145) and SUD treatment utilization

(a) Of 479 observations over 18 months (N = 242):

-Medically managed withdrawal: 7.5%

-Residential SUD treatment: 4%

-Methadone treatment: 28.8%

-Outpatient SUD counseling: 9.6%

(b) Using vs. not using the mobile program [AOR (95% CI)]:Used inpatient SUD treatment [4.2 (2.1–8.1)]

Used outpatient SUD counseling [6.1 (2.6–14.2)]

Gervasoni, 2012, Switzerland [25]

Cross-sectional

SSP participants (N = 921)

Differences between those receiving methadone (n = 525) vs. not receiving (n = 386)

Receiving vs. not receiving methadone [AOR (95% CI)]: Female sex [1.6 (1.1–2.32)]; Age [1.38 (1.19–1.61)]; Lifetime injection [2.26 (1.52–3.36); HIV positive [2.69 (1.48–4.87)]; HCV positive [1.96 (1.49–2.60)]; Daily SSP visits [0.54 (0.41–0.72)]

Hagan, 2000, US (Seattle) [26]

Cohort study

PWID recruited from methadone and other SUD treatment programs, a correctional facility, and a street outreach and social service agency (N = 2879)

Differences between Ex-, Current, New, and Never SSP-users in:

(a) Change in injection frequency

(b) Entry into methadone treatment

(a) Reduced injection risk by 75% or more:

Ex-SSP-users vs. Never SSP-users [ARR 2.85 (1.47–5.51)]; Ex-SSP users vs. Never SSP-users who inject daily or more [ARR 3.44 (1.46–8.09)]

Stop injecting altogether: Ex-SSP users vs. Never SSP users (ARR 3.5, 95% CL 2.1–5.9))

(b) New vs. Never SSP users (ARR 5.05 [1.44–17.7)]

Heimer, 1998, US (New Haven) [28]

Cohort study

SSP participants (N = 1905)

(a) SSP participant characteristics associated with requesting treatment (all types) (n = 409) vs. not requesting treatment (n = 1496)

(b) Factors associated with entering SUD treatment

(a) Treatment requesters vs. non-requesters:

Female: 29.3% vs. 21.6% (p < 0.01)

Race/ethnicity (p < 0.001)

African American: 46.5% vs. 36.2%

Latino: 26.7% vs. 20%

White: 20.3% vs. 42.8%

(b) 442 appointments made with 60% resulting in treatment entry. Barriers to entry include: treatment delays (< p = 0.01), no insurance

(p < 0.01), cocaine use (p < 0.01)

Hudoba, 2004 Australia (New South Wales) [72]

Pre-Post

SSP workers (N = 6)

(a) Changes in referrals after

staff training in counseling and harm reduction

(b) Change in staff knowledge and confidence

(a) Referral rates (pre- to post-) for:

Drug treatment: 44% to 49% (p < 0.01)

Health and medical services: 23% to 28% (p < 0.01)

(b) Changes (pre- to post-) in:

Staff knowledge (p < 0.01) Confidence (p = 0.05)

Kidorf, 2010, US (Baltimore) [73]

Analysis of RCT data

Newly registered SSP participants who inject opioids (N = 281)

Association between psychiatric symptoms (global severity index (GSI) on the psychiatric Symptom Checklist-90) and treatment entry

High vs. low GSI scores predicted more treatment enrollment: AOR 2.15 (1.10–4.23)

Latkin, 2006, US (Baltimore) [27]

Cohort study

Out-of-treatment PWID (N = 440)

Characteristics associated with treatment entry (n = 166) vs. no treatment entry (n = 274)

Type of SUD treatment received:

Medically managed withdrawal: 28.9%;

Methadone treatment: 74.7%; Residential treatment: 22.3%; Outpatient program: 25.3%

Characteristics associated with treatment entry:

Recent SSP use [AOR 1.71, (1.12–2.62)]; Female sex [AOR: 1.77 (1.13–2.75)]; Recent intranasal cocaine use [AOR: 0.44, 0.21–0.91)]

Riley, 2002, US (Baltimore) [24]

1) Cohort study

2) Cross-

Sectional study

1) SSP participants from a single SSP (N = requesting methadone treatment referral (N = 2659)

2) Survey respondents from 6 SSPs (N = 102)

1) Characteristics associated with requesting referral to SUD treatment (n = 139) vs. not requesting referral (n = 2520); Characteristics of referred patients who entered methadone treatment (n = 39) vs. did not enter methadone treatment (n = 100)

2) Patient reported barriers to entering treatment

1) AORs for requesting SUD treatment: Age > 38 [1.96 (1.63–2.37)]; Female sex [2.02 (1.63–2.37)]; Use speedballs in past 6 months [3.83 (3.14–4.66)]; > 20 years old at first injection [1.59 (1.31–1.94)]

AORs for entering methadone treatment:

Male [2.45 (1.04–5.78)]

2) Common barriers included: lack of health insurance, lack of treatment slots, residing too far from treatment facility, employment schedule conflicts, incarceration, expectation of overwhelming or difficult paperwork

Strathdee, 1999, US (Baltimore) [29]

Cohort study

PWID (N = 1483)

1) Predictors of entry into medically managed withdrawal by HIV status, including SSP attendance

AORs for entry into medically managed withdrawal (among HIV negative and HIV positive): Injecting > once/day [2.03 (1.48–2.78) and 2.98 (1.66–5.35)]; Injecting speedballs or heroin [2.22 (1.3–3.77)] (HIV positive only); Admitted to hospital [4.0 (3.08–5.19) and 2.82 (1.28–4.38)]; Visited physician [1.92 (1.28–2.89)] (HIV positive only); Health insurance [1.51 (1.01–2.28)] (HIV positive only); Attended SSP [1.38 (1.02–1.87) and 3.2 (1.38–7.53)]

Surratt, 2020 US (Appalachian Kentucky) [32]

Cross-sectional

PWID from 3 SSPs (N = 186)

Characteristics of SSP participants associated with current treatment participation

Uptake of the SSP: 44.6% had 6 + visits over the past 6 months

AORs for current treatment participation: 6 + SSP visits/6 months [1.368 (0.557–3.362)] (NS); Confident in reducing substance use [2.241 (1.002–5.009)]; Primary injection drug methamphetamine [0.341 (0.146–0.798)]