Prevalence and patterns of polydrug use
In total, 4,496 MSM participated in our study, and 1275 (28.4%) reported using RDs in the past 6 months. Of these, 82.4% (n = 1050, 23.4% of all participants) used one type of RD (one-type-RD-users, 1DUs), 12.2% (155, 3.4%) used two types of RDs (2DUs), and 5.5% (70, 1.6%) used ≥3 types of RDs (3DUs).
Among 1DUs, most used poppers (90.9%), followed by codeine (3.2%), and methamphetamine (2.8%). Among 2DUs, 91.6% used poppers, 57.4% used methamphetamines, and 23.9% used ecstasy. Among 3DUs, 95.7% used poppers, 74.3% used methamphetamines, and 71.4% used ecstasy. Among all participants, 5.0% (n = 225, 17.6% of RD users) used two or more types of RDs (i.e., polydrug use). These polydrug users commonly took poppers accompanied with one or more types of other RDs (e.g., methamphetamine) simultaneously or within the same time period (Figure 1).
Characteristics of polydrug users
MSM aged 26–30 years had the highest prevalence of RD use in the past 6 months for all types of RD use (i.e., 1DUs, 2DUs, and 3DUs). Except for between age and ≥3 types of RDs used (P = 0.594), there was a significant association between age and the different RD subgroups (P < 0.001 for all). Also, the proportion of MSM aged 26–30 years increased as the number of RDs used in the past 6 months increased (P < 0.001 for trend) (Table 1).
For all the other social demographics examined, participants who were internal migrants, had a monthly income ≥600 USD, used versatile positions during anal intercourse, and who had inadequate knowledge about prevention of HIV infection had the highest prevalence of for all types of RD use in the past 6 months. Also, the proportions of these demographics increased significantly as the number of RDs used in the past 6 months increased (P < 0.05 for trend). Although participants with educational attainment of junior school or below had the lowest prevalence for use of one type of RD in the past 6 months, the prevalence of use of two or more types of RDs in the past 6 months was significantly higher (P < 0.05 for all) (Table 1).
Characteristics of HIV high-risk behaviors
For almost all the HIV high-risk behaviors examined (e.g., seeking male sexual partners through the Internet in the past 6 months, having group sex in the past 6 months), the prevalence of HIV high-risk behavior was higher among those who used RDs in the past 6 months compared with those who did not, and there was a significant association between the HIV high-risk behavior and RD subgroup (P<0.05 for all). In general, the prevalence of HIV high-risk behaviors increased as the number of RDs used in the past 6 months increased (Table 2).
Prevalence and incidence of HIV based on RD use
The HIV prevalence (13.7%, 95%CI: 11.7–15.9 vs. 8.8%, 95%CI: 7.8–9.8) and HIV incidence [13.1 infections per 100 person- years (PY), 95%CI: 9.8–16.3 vs. 7.7 infections per 100 PY, 95% CI: 6.3–9.1] were higher among 1DUs compared with participants who did not use RDs in the past 6 months. In contrast, the HIV prevalence (8.4%, 95%CI: 4.5–13.9; 7.1%, 95%CI: 2.4–15.9) and HIV incidence (9.7 infections per 100 PY, 95%CI: 2.5–16.9; 2.4 infections per 100 PY, 95%CI: –2.3–7.0) of 2DUs and of 3DUs were not significantly higher than those who did not use RDs or of 1DUs in the past 6 months (Table 3a).
Association between RD use and HIV infection
After adjustment for social demographics, 1DUs had higher odds of established HIV infection (AOR = 2.1, 95%CI: 1.5–2.8) and higher odds of recent HIV infection (AOR = 2.2, 95%CI: 1.5–3.0) compared with those who did not use RDs. 2DUs also had higher odds of recent HIV infection (AOR = 2.3, 95%CI: 1.0–5.2) compared with those who did not use RDs. In contrast, 2DUs and 3DUs did not have significantly higher odds of established HIV infection compared with those who did not use RDs (Table 3b).
PAFs of high-risk behaviors for HIV infection
The PAFs of most HIV high-risk behaviors for recent HIV infection (except for men who had >2 male sexual partners in the past 6 months and those who had commercial sex in the past 6 months) were higher among polydrug users in the past 6 months compared with those who did not use RDs or among 1DUs. However, this relationship of higher PAFs of HIV high-risk behaviors as the number of RDs used in the past 6 months increased was not shown consistently in relation to established HIV infection. Finally, most of the PAFs of HIV high-risk behaviors for recent HIV infection were higher compared with the PAFs of the corresponding HIV high-risk behaviors for established HIV infection (Figure 2).