This study found that in the year of 2018, the percentage of identified PLWHAs reported to be transmitted through CMNCHC is 12.54% higher than through CHC in non-marital heterosexual transmission in China. The enhanced proportion of transmission through NMNCHC implicated to a certain extent that HIV is spreading gradually from the high-risk population to the general. Moreover, there were significant differences in the socio-demographic characteristics of cases transmitted through NMNCHC and CHC.
In the transmission of CHC, the proportion of males was 13.33 times higher than that of females, in contrast, the distribution ratio of males and females in NMNCHC was much more balanced, with males being only 1.52 times that of females. After controlling for other factors, the odds of females to be transmitted through NMNCHC was 8.39 times that of males. All of this suggests that males were more likely to be infected through CHC, while females had a much higher proportion to be infected through NMNCHC. Some studies suggested that clients of female sex workers (FSWs) were important bridges to spread HIV from high-risk groups to the general population through heterosexual behavior, making them a key target for intervention(15, 16). The chain of transmission is such that the clients of FSWs become infected with HIV through CHC, which is transmitted to the general females through NMNCHC, and the infected general females continued to transmit other males through NMNCHC, and HIV then began to spread among the general population.
This study found that younger people were more likely to be infected through NMNCHC, while older people were more likely to be infected through CHC. People over 50 years old are still sexually active, and they may seek sex with FSWs or casual partners, especially those who do not have spouses or stable sexual partners(17, 18). The aphrodisiac usage promoted this behavior and enhanced the risk(19). Furthermore, since HIV prevalence among low-tier FSWs was high and older people were more likely to be engaged in sexual behavior with the low-tier FSWs, hence they were at high risk for HIV infection through this channel(20). All these factors could contribute to the enhanced possibility of older people being transmitted through CHC. By contrast, the higher possibility of young people infected through NMNCHC was probably due to that they were more likely to be engaged in casual sex and the growth of social networking platforms had made casual sex more accessible. A study of 735 male bachelors found that 16.5 percent of the sample had experienced causal sex with someone they met online, and they were more inclined to engage in high-risk sex when having sex with those partners, and more likely to be 28 ~ 35 years old(21).
The odds of being transmitted through NMNCHC among minorities were 94% higher than Han Chinese. It was common for some ethnic minorities in China to have multiple casual sexual partners due to their traditional beliefs on marriage and open attitude towards sex. For instance, casual sex had already become the predominant risk factor for HIV transmission now in Liangshan, where feature populations composed primarily of ethnic minorities(22). One study interviewed 108 Yi villagers aged 15 ~ 35 in Liangshan Yi ethnic minority region, they found that 82.4% of the young people had casual sex behaviors, 54.9% of which never used condoms(23).
Those who live in the different city of the same province had higher odds to be reported as infected through NMNCHC compared with the resident in the same county. Studies found that migrants were vulnerable to risky sexual behaviors(24). Rural-to-urban migrant males were significantly less likely to report condom use at first sex and consistent contraceptive use with first partner compared to non-migrants and urban-to-urban migrants(25). The reasons why migrants of different provinces were more likely to be transmitted through CHC while migrants of different city in the same province were more likely to be reported to be transmitted through NMNCHC still need further study. This may be due to the higher proportion of rural-to-urban migrants in different cities within the same province, or the greater availability of commercial services in provinces with more migrations from other provinces.
PLWHAs with higher levels of education and occupations other than farming were more likely to report infection through NMNCHC. It was probably due to their relatively higher socioeconomic status and stronger competence to obtain more non-marital non-commercial sexual partners. By contrast, people of relatively low socioeconomic status are more likely to patronize low-end FSWs, significantly increasing the likelihood of infection through CHC. Moreover, in multivariate analysis, there was little difference in marital status between the two types of heterosexual transmission routes. Further research is needed to explore the reasons behind these phenomena.
Limitations
For reasons such as stigmatization or social desirability, some MSM might report to be transmitted through heterosexual transmission, either CHC or NMNCHC, while some females may be sex workers but reported to be transmitted through NMNCHC. Furthermore, it is possible for both genders to be reported as sexual transmission, while they were actually infected through drug abuse. Although the data collectors on the front line would have some control and judgment to avoid misreport, the proportion of heterosexual transmission could still be overestimated to some extent. Because the data is self-reported, the possibility of these misstatements is difficult to eliminate, and further research is required to determine the extent to which false reports of transmission routes exist and how much they affect the overall transmission routes distribution.
Although China had made great achievements in the HIV prevention of high-risk groups, transmission through CHC still accounts for a high proportion, suggesting that there are still blind spots in the prevention and control of commercial sex transmission. On the other hand, for NMNCHC, a transmission route that is most widespread and hidden, as well as the most difficult to control, effective prevention strategy shall be developed according the features of this population, so as to realize early prevention.