Demographic characteristics
A total of 21,596 FSWs were recruited in this study over nine years. The demographic characteristics were shown in Table 1. Among all the participants, 19,873 (92.0%) were LCFSWs and 1,723 (8.0%) were CMFSWs. It is worth noting that all of the CMFSWs in our study were from Vietnam. Additionally, results showed that CMFSWs were more likely to be unmarried, divorced or widowed, receiving primary school or illiterate of education, working in low-tier venues, reporting a shorter time of staying in current residence, a shorter length time as a commercial sex worker and a younger age at commercial sexual debut than LCFSWs.
Prevalence of HIV-1, syphilis and HCV infection
The overall prevalence of HIV-1 and syphilis infection among all the participants was 0.91% (197/21596) and 5.14% (1109/21596), respectively, and remained relatively stable during the study period. However, as shown in Figure 1, the HIV-1 prevalence among LCFSWs significantly decreased from 2010 to 2018 (OR=0.922, 95% CI: 0.859-0.989; p for trend=0.024), but this trend was not found among CMFSWs. Furthermore, higher HIV-1 and HCV prevalence was observed among CMFSWs than LCFSWs (HIV-1: 3.13% versus 0.72%, p<0.001; HCV: 2.09% versus 1.05%, p<0.001), though HCV prevalence significantly decreased among CMFSWs from 2010 to 2018 (OR=0.845, 95% CI: 0.726-0.983; p for trend=0.029). There was no statistical difference in the prevalence of syphilis infection between LCFSWs and CMFSWs (5.15% versus 4.93%, p=0.838), and there was no significant change in the trend of syphilis infection of the two groups.
Behavioural characteristics and self-reporting of STIs
As shown in Table 2, compared to LCFSWs, CMFSWs were more likely to use illicit drugs, sex with regular commercial sexual partners in the past month, but less likely to use condoms in last commercial sex and in the last month, have steady non-paying sexual partners and sex with commercial male clients who used aphrodisiac drugs. The proportion of participants who insisted on using condoms in last commercial sex and in last month were both gradually increased among LCFSWs (OR=1.364, 95% CI: 1.315-1.415; OR=1.344, 95% CI: 1.319-1.369) and CMFSWs (OR=1.242, 95% CI: 1.122-1.375; OR=1.123, 95% CI: 1.061-1.188). Illicit drugs use in lifetime was gradually increased among LCFSWs (OR=1.075, 95% CI: 1.020-1.134), while it was gradually decreased among CMFSWs (OR=0.771, 95% CI: 0.666-0.892). Downward trends were also found in the number of male clients in the past month (OR=0.915, 95% CI: 0.847-0.987), sexing with regular commercial sexual partners in the past month (OR=0.892, 95% CI: 0.830-0.959) and having steady non-paying sexual partners (OR=0.837, 95% CI: 0.752-0.932) among LCFSWs. CMFSWs also reported a decreasing trend of sexing with regular commercial sexual partners in the past month in the study period (OR=0.375, 95% CI: 0.301-0.467). The difference of Self-reporting of STIs in the last year between LCFSWs and CMFSWs was not statistically significant, but gradually increased among the LCFSWs (OR=1.052, 95% CI: 1.021-1.084).
HIV-/AIDS-related knowledge and intervention services
As shown in Table 2, during the nine-year period, the awareness rate of HIV/AIDS-related knowledge among LCFSWs was statistically higher than that of CMFSWs (93.71% versus 86.76%, p<0.001), with an increasing trend among LCFSWs (OR=1.239, 95% CI: 1.208-1.272), while there was no significant change among CMFSWs. A higher proportion of receiving free condom distribution programme could be found among LCFSWs than CMFSWs (96.12% versus 89.61%, p<0.001). However, CMFSWs were more likely to receive methadone maintenance therapy or needle exchange and peer education programmes. There was a significant increase in the utilization of free condom distribution (OR=1.116, 95% CI: 1.082-1.151), methadone maintenance therapy or needle exchange programmes (OR=1.076, 95% CI: 1.015-1.140) and peer education programmes (OR=1.048, 95% CI: 1.036-1.061) among LCFSWs. Increasing trend was also found in peer education programme (OR=1.078, 95% CI: 1.031-1.127) among CMFSWs, however, the trend of receiving methadone maintenance therapy or needle exchange programme among CMFSWs was decreased (OR=0.657, 95% CI:0.546 -0.790).
Risk factors associated with HIV-1 infection
From 2010 to 2015, as shown in Figure 2, there were four common risk factors for HIV-1 infection among both LCFSWs and CMFSWs: age >35 years old, unmarried/divorced/widowed, staying in current residence >12 months and self-reporting of STIs in the last year. Beyond that, primary school or illiterate education background (OR=4.304, 95% CI: 1.294-14.316), illicit drugs use (OR=6.476, 95% CI: 1.840-22.793) and syphilis infection (OR=2.625, 95% CI: 1.541-4.473) were significantly associated with HIV-1 infection among LCFSWs. However, LCFSWs had lower odds to be HIV-1 infected if they had been staying in current residence for 6~12 months (OR=0.395, 95% CI: 0.164-0.949). From 2016 to 2018, the risk factors for HIV-1 infection among LCFSWs and CMFSWs were different. For CMFSWs, self-reporting of STIs in the last year (OR=18.975, 95% CI: 2.403-149.805), inconsistent condoms use in commercial sex in the past month (OR=4.827, 95% CI: 1.271-18.331) and HCV infection (OR=13.799, 95% CI: 1.560-122.020) were significantly associated with HIV-1 infection, while receiving peer education programme in the past year (OR=0.131, 95% CI: 0.030-0.564) presented a protective effect for HIV-1 infection. Regarding to LCFSWs, an unmarried/divorced/widowed status (OR=2.989, 95% CI: 1.298-6.884) and engaging in commercial sex with male clients who used aphrodisiac drugs (OR=4.369, 95% CI: 1.746-10.937) were significantly associated factors for HIV-1 infection.
Risk factors associated with syphilis infection
As shown in Figure 2, self-reporting of STIs in the last year and HCV infection were both related to syphilis infection among LCFSWs and CMFSWs from 2010 to 2015. Staying in current residence for 6~12 months and over 12 months were associated with syphilis infection in CMFSWs and LCFSWs, respectively. In addition, inconsistent condoms use in commercial sex in the past month (OR=2.635, 95% CI: 1.285-5.400) was significant risk factor for syphilis infection among CMFSWs, while low-tier working venues, age >35 years old, primary school or illiterate and junior middle school education background, inadequate HIV/AIDS-related knowledge, illicit drug use and HIV infection were risk factors for syphilis infection among LCFSWs. The marital status of unmarried/divorced/widowed presented a protective effect for syphilis infection among LCFSWs. During 2016-2018 period, low-tier working venues and self-reporting of STIs in the last year were both related to syphilis infection among LCFSWs and CMFSWs. Engaging in commercial sex with male clients who used aphrodisiac drugs (OR=20.813, 95% CI: 4.708-92.018) was significantly associated factor for syphilis infection among CMFSWs. Regarding to LCFSWs, working as commercial sex worker >5 years (OR=1.443, 95% CI: 1.086-1.917) and HCV infection (OR=7.182, 95% CI: 3.244-15.897) were associated with syphilis infection.