| 
      OR: Odds ratio; CI: confidence interval.
        | Factors | Participants who    injected drugs in last 3 months | Unadjusted OR (95%    CI) | P- value | Adjusted OR (95%    CI) | P- value
 |  
        | N (%) |  
        | Age  |   10 (20.8) |   | 0.04 |   |   |  
        | ≤20    years old | 1 |   |   |   |  
        | >20 years old | 163 (35.8) | 2.1 (1.0, 4.4) |   |   |   |  
        | Sex |   53 (27.2) |   | <0.01 |   | <0.01 |  
        | Female | 1 |   | 1 |   |  
        | Male | 120 (38.8) | 1.7 ( 1.2, 2.5)  |   | 1.9 (1.2, 3.2) |   |  
        | Ethnicity |   |   | <0.01 |   |   |  
        | Han majority | 104 (44.6) | 1 |   |   |   |  
        | Yi orother minorities | 69 (25.5) | 0.4 (0.3, 0.6) |   |   |   |  
        | Year of schooling |   |   | <0.01 |   |   |  
        | ≤6    years | 72 (26.7) | 1 |   |   |   |  
        | >6 years | 101(43.2) | 2.0 (1.4, 3.0) |   |   |   |  
        | Currently employed |   |   |   | 0.11 |   |   |  
        | No  | 119 (32.3) | 1 |   |   |   |  
        | Yes  | 54 (40.0) | 1.4 (0.9, 2.1) |   |   |   |  
        | Marital status |   |   | 0.03 |   |   |  
        | Currently married | 42 (27.3) | 1 |   |   |   |  
        | Other | 131 (37.4) | 1.6 (1.1, 2.4) |   |   |   |  
        | Personal annual income    (US $)  |   |   | <0.01 |   |   |  
        | ≤1400 | 66 (26.9) | 1 |   |   |   |  
        | >1400 | 107 (41.3) | 1.9 (1.3, 2.8) |   |   |   |  
        | Duration of drug    use |   |   | <0.01 |   |   |  
        | < 6.0 years | 74 (25.4)  | 1  |   |   |   |  
        | ≥6.0 years | 99 (46.5) | 2.5 (1.7, 3.7) |   |   |   |  
        | Primary partner ever used drugs  |   |   | <0.01  |   | <0.01  |  
        | No  | 138 (31.2)  | 1 |   | 1 |   |  
        | Yes  | 35 (57.4)  | 3.0 (1.7, 5.1)  |   | 3.3 (1.7, 6.5)  |   |  
        | Frequency of orally    using heroin in last 3 months |   |   | <0.01 |   | <0.01 |  
        | <7 times/week | 91 (51.4) | 1 |   | 1 |   |  
        | ≥7 times/week | 82 (25.1) | 0.3 (0.2, 0.5) |   | 0.3 (0.2, 0.5) |   |  
        | Currently participating    in MMT |   |   | 0.97  |   |   |  
        | No | 164 (34.3) | 1 |   |   |   |  
        | Yes | 9 (34.6) | 1.0 (0.4, 2.3) |   |   |   |  
        | Ever had HIV test |   |   | <0.01 |   |   |  
        | No | 58 (25.6) | 1 |   |   |   |  
        | Yes | 115 (41.5) | 2.1 (1.4, 3.0) |   |   |   |  
        | Had unprotected sex    with a primary sex partner in last 30 days |   |   | <0.01 |   |   |  
        | No | 84 (28.9) | 1 |   |   |   |  
        | Yes | 89 (41.8) | 1.8 (1.2, 2.6) |   |   |   |  
        | Had unprotected sex    with non-primary sex partners in last 30 days |   |   | <0.01 |   | <0.01 |  
        | No |   | 1 |   | 1 |   |  
        | Yes | 55 (57.3) | 3.3 (2.1, 5.2) |   | 2.7 (1.6, 4.6)  |   |  
        | Paid money for sex    or exchanged sex for money in last 6 months |   |   | <0.01 |   |   |  
        | No | 127 (30.2) | 1 |   |   |   |  
        | Yes | 46 (55.4) | 2.9 (1.8, 4.7) |   |   |   |  
        | Ever had more than  one episode of detoxification |   |   | <0.01 |   | <0.01 |  
        | No | 50 (20.1) | 1 |   | 1 |   |  
        | Yes | 123 (48.2) | 3.7 (2.5, 5.5) |   | 3.7 (2.3, 6.0) |   |  
        | Ever participated in HIV prevention program |   |   | <0.01 |   | 0.06 |  
        | No | 68 (24.5)  | 1 |   | 1 |   |  
        | Yes | 105 (46.5) | 2.7 (1.8, 3.9) |   | 1.6 (1.0, 2.5) |   |  |