Table 2.
Bivariate analysis of factors associated with heroin–methamphetamine co-injection in the past 6 months among persons who inject drugs in San Diego and Tijuana (N = 1,311)
| Variable | Overall (N = 1,311) | Co-injected (n = 522) | Did not co-inject (n = 773) | p |
| Background | ||||
| Female, n (%) | 428 (32.7%) | 179 (34.3%) | 244 (31.6%) | .232 |
| Completed high school or preparatoria, n (%) | 294 (22.5%) | 91 (17.4%) | 198 (25.5%) | <.001 |
| Homeless/unstable housing, n (%) | 499 (38.1%) | 193 (37.0%) | 296 (38.3%) | .631 |
| Born in city of residence, n (%) | 467 (35.7%) | 181 (34.7%) | 282 (36.5%) | .544 |
| Age, Mdn (IQR) | 39 (32, 48) | 38 (31, 45) | 42 (32, 50) | <.001 |
| Years in region, Mdn (IQR) | 24(11, 36) | 21 (10, 34) | 25 (12, 37) | <.001 |
| Age at first injection, Mdn (IQR) | 20(17, 25) | 19(16, 24) | 20(17, 27) | .002 |
| Years since first injected, Mdn (IQR) | 17 (9, 27) | 16(8, 24) | 18(9, 29) | <.001 |
| Cohort (ref.: San Diego), n (%) | 735 (56.1%) | 411 (78.7%) | 324 (41.9%) | <.001 |
| Injection risk behavior, past 6 months, n (%) | ||||
| Receptive syringe sharing | 814(64.3%) | 393 (76.3%) | 412 (55.8%) | <.001 |
| Distributive syringe sharing | 822 (65.8%) | 394 (77.0%) | 418 (54.2%) | <.001 |
| Cooker, cotton, water sharing | 855 (53.8%) | 391 (75.5%) | 454 (60.9%) | <.001 |
| Shared unbleached syringe | 681 (58.5%) | 347 (67.4%) | 325 (44.0%) | <.001 |
| Divided drugs with syringe | 727 (58.5%) | 347 (68.5%) | 371 (51.2%) | <.001 |
| Purchased prefilled syringe | 135 (10.3%) | 87(16.3%) | 50 (6.5%) | <.001 |
| Sex risk behavior, past 6 months, n (%) | ||||
| ≥2 casual partners | 424 (32.5%) | 183 (35.0%) | 239 (31.1%) | .111 |
| Unprotected sex with casual partner | 421 (32.3%) | 182 (35.1%) | 236 (30.7%) | .095 |
| Exchanged sex | 266(21.4%) | 146 (29.1%) | 119(16.3%) | <.001 |
| Drug use before or during sex | 972 (74.8%) | 406 (78.4%) | 556 (72.4%) | .015 |
| HIV and overdose, n (%) | ||||
| Ever overdose | 639 (48.9%) | 312(59.8%) | 320 (41.5%) | <.001 |
| Past-6-month overdose | 119(9.1%) | 66 (12.6%) | 49 (6.4%) | <.001 |
| Tested HIV positive | 78(6.1%) | 19 (3.7%) | 58 (7.7%) | .003 |
| Need for harm-reduction services, n (%) | ||||
| Hard to obtain sterile syringes | 229(17.5%) | 115 (22.1%) | 110(14.3%) | <.001 |
| Great/urgent need for help for drug use | 594 (45.6%) | 274 (52.8%) | 311 (40.4%) | <.001 |
Notes: IQR = interquartile range; ref. = reference.