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Table 1 List of parameters, distributions, and sources

From: Economic evaluation of the effect of needle and syringe programs on skin, soft tissue, and vascular infections in people who inject drugs: a microsimulation modelling approach

Parameters

Values

Distribution

Source

Number of cyclesa

260 weeks

  

Cycle length

1 week

  

Annual discount rate (costs)

1.5%

Sensitivity analysis (0–3%)

[56]

Annual discount rate (utilities)

1.5%

Sensitivity analysis (0–3%)

[56]

Number of PSA samples

1000

  

Weekly incidence proportion of SSTVI (median)

0.001452

5%: 0.00097

95%: 0.00296

Administrative data

Weekly probability of SSTVI (median)

0.001458

5%: 0.00097

95%: 0.00302

Administrative data

PWID Characteristics

 % PWID who used needles/syringes used by someone else

19.6

Beta (1709, 7009)

[46]

 % PWID reusing their own needles

29.7

Beta (77, 182)

[72]

 % of injections that involved use of needles-syringes that someone else used

  

[46]

  None

85.0

6410 out of 7546

 

  1–20%

10.1

766 out of 7546

 

  21–100%

4.9

370 out of 7546

 

 % Male

62

 

Administrative data

 Years of injection drug use (%)

  

Administrative data

  < 2 years

40.12

  

  2- < 5 years

35.55

  

  5- < 8 years

18.16

  

  8 or more years

6.16

  

 Injection frequency in the past month (%)

  

[46]

  Never

12.9

1136 out of 8787

 

  Not every week

22.2

1949 out of 8787

 

  1–2 days a week

15.6

1366 out of 8787

 

  3–6 days a week

14.4

1270 out of 8787

 

  Every day

34.9

3066 out of 8787

 

 Number of injections in the past month (%)

  

[46]

  1–4

16.9

1268 out of 7519

 

  5–10

14.2

1067 out of 7519

 

  11–20

12.3

925 out of 7519

 

  21–40

10.0

750 out of 7519

 

  41–60

9.4

704 out of 7519

 

  61–100

11.1

833 out of 7519

 

  101–200

15.0

1125 out of 7519

 

  201–9000

11.3

847 out of 7519

 

Risk of SSTVI

 Male (versus Female)

1.14

95% CI = 1.08–1.19

Administrative data

 Age

  

Administrative data

  < 25

REF

  

  25–44

1.19

95% CI = 1.15–1.23

 

  45+

1.07

95% CI = 1.03–1.11

 

 Needle sharing

3.31 (IRR)

95% CI = 2.04–5.37

[18]

 Reusing needles/syringes

2.1 (OR)

95% CI = 1.2–3.7

[16]

 Injection frequency

  

[16]

  Once per week

REF

  

  2–7 times a week

2.1 (OR)

95% CI = 1.1–4.0

 

  More than once a day

3.1 (OR)

95% CI = 1.7–5.5

 

 Number of attempts to achieve injection

  

[16]

  1

REF

  

  2

2.6 (OR)

95% CI = 2.0–3.5

 

  3

3.7 (OR)

95% CI = 2.7–5.2

 

  4+

3.8 (OR)

95% CI = 2.8–5.1

 

 Years of injection drug useb

  

[19]

  < 1 year

REF

  

  2–4 years

2.49 (OR)

95% CI = 1.16–5.34

 

  5–7 years

3.95 (OR)

95% CI = 1.73–9.02

 

  8–10 years

4.84 (OR)

95% CI = 2.14–10.92

 

Needle and syringe program

 Risk of sharing injection equipment

0.42 (RR)

95% CI = 0.25–0.72

[34]

 Risk of reusing syringes

0.79 (RR)

95% CI = 0.66–0.95

[34]

Costs

 NSP

$322.07

Annual cost of NSP per person in 2022 CAD

[61]

 Purulent SSTVI

  

Administrative data

  Outpatient

$100.78

Scale = 76.28

Shape = 1.32

 

  ED

$1135.70

Scale = 91.54

Shape = 12.41

 

  Inpatient

$6022.35

Scale = 5994.01

Shape = 1.00

 

  Inpatient complications

$42,526.40

Scale = 70,215.26

Shape = 0.61

 

 Non-purulent SSTVI

  

Administrative data

  Outpatient

$93.73

Scale = 72.40

Shape = 1.29

 

  ED

$1144.64

Scale = 100.93

Shape = 11.34

 

  Inpatient

$6821.06

Scale = 6119.28

Shape = 1.11

 

  Inpatient complications

$41,016.23

Scale = 66,790.89

Shape = 0.61

 

Utilities

 PWID multiplicative factor

0.9

 

[73]

Ambulatory Care

 Cellulitis

0.97607

 

[52, 53]

 Abscess

0.97607

 

[52, 53]

Hospitalization

 Abscess

0.642

 

[52]

 Cellulitis

0.642

 

[52]

  1. CAD Canadian dollar, IRR Incidence rate ratio, NSP Needle and syringe program, OR Odds ratio, PSA Probabilistic sensitivity analysis, PWID People who inject drugs, QALY Quality-adjusted life-year, REF Reference, RR Risk ratio, SSTVI Skin, soft tissue, and vascular infections
  2. aThe time horizon for this study was 5 years, and we assumed that each year had 52 weeks
  3. bDue to the nature of administrative data, there remained uncertainty in capturing the duration of injection drug use among individuals identified as PWID. We assumed that PWID identified in the administrative databases had initiated injection drug use 6 months before being captured in the data. This resulted in small percentage of individuals in the ‘ < 1 year of injection drug use’ category. To account for this, we set ‘ < 2 years’ of injection drug use as the reference category. Based on patient information from the administrative data, we created the remaining categories of duration of injection drug use as ‘2–5 years’, ‘5–8 years’, and ‘> 8 years’ for the analysis
  4. Note: The results in this Table, whose source is ‘administrative data’, were compiled using data from the © Government of Québec (Research file publication date: 2009–2019; Data use approval date: 20 September 2021)
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