| City | Number of seeds | Recruitment procedure | Recruitment sample size N (%) | |||
|---|---|---|---|---|---|---|
| RDS | Select peer recruitment | Total recruited | Completed the survey | Eligible for data analysis | ||
| Hanoi | 23 | 105 | 97 | 225 | 179 | 168 (28.8) |
| Haiphong | 19 | 158 | 66 | 243 | 217 | 213 (36.5) |
| Ho Chi Minh City | 30 | 91 | 114 | 235 | 208 | 203 (34.8) |
| Total | 72 | 354 | 277 | 703 | 604 | 584 |