Main findings of this study
In this cross-selectional study, the overall utilization rate of HCT services was 7.7%, which was higher than the rates reported by other authors [7,8,9,10,11], but lower than the level (14.9%) calculated by Qin, Gao, Zhu, Zhang, Kong and Chen . Similar to previous studies’ findings, a vast majority of students expressed their willingness to use HCT services [7, 14] and felt the necessity of providing HCT services on college campuses . However, feeling no necessity of being tested (67.3%) and not knowing where to get an HIV test (18.1%) were cited as major reasons for non- participation. Furthermore, our study also added to the growing body of evidence that the discordance existed between self-perceived and reported HIV risk [23,24,25]. Based on the analysis of Pringle et al. (2013), this discordance might be caused by optimistic bias (the belief that negative events are less likely to befall on oneself than others), denial and distancing (refusal to accept an unpleasant truth), and downward comparison (when a person compares oneself to those less fortunate) . This underscores the urgent need for promoting self-realization of HIV risk [8, 10, 24] when launching a large-scale testing campaign among college student in order to achieve the ambitious “95–95-95″ targets by 2030  and the final goal of three Zeros.
Based on the Andersen’s behavioral model, this study revealed that HCT uptake was inequitably distributed, since it was mainly influenced by predisposing and enabling factors rather than need factors of undergraduates. More specifically, HCT uptake was significantly related to six predisposing factors (sexual orientation, major, grade, HIV-related knowledge, willingness to utilize HTC services and recognition of the necessity to provide HCT), one enabling factors (knowledge of local AIDS service organization) and two need factors (condomless sex and perception of HIV risk).
The effects of sexual orientation were consistent with a meta analysis conducted by Shi et al. in 2018 in which non-heterosexuals men were more likely to utilize HCT services . This phenomenon could be explained by the following two factors. First, previous HIV educational campaigns focused primarily on individuals at high risk for HIV infection such as men who have sex with men and sex workers, which might perpetuate the belief that participants’ social identities, rather than their risky sexual behaviors were closely correlated with HIV risk. Second, condomless anal intercourse is considered the highest-risk sexual behavior and male-male sexual contact remains the predominant mode of HIV transmission among Chinese young students.
Older students (i.e., non-freshmen) were found to be more likely to utilize HCT services than younger individuals, possibly due to the fact that the chances of being exposed to HIV infection and subsequent risk perception increases with age. As with our previous study , medical students and those who knew about free HIV testing centers were more likely to utilize HCT services. These findings support the idea that exposure to accurate levels of HIV and AIDS information through the media, health education and access to HCT services may improve the knowledge about risks for HIV infection and dispel the stigma associated with HIV infection, which can help to a certain extent to reduce optimistic bias and finally contribute to accurate risk perception and actual use of HCT services.
Compared to their respective counterparts, students with more knowledge of HIV transmission and those who expressed their willingness to use HCT services and felt the necessity of providing HCT services on college campuses were found to be less likely to utilize HCT services. This finding is not surprising as it fits knowledge- attitude-belief-practice model. Meanwhile, our data also indicated that those with higher levels of knowledge were more likely to have positive attitudes and practices towards preventive health measures, and were consequently less likely to engage in risky sexual activities (See Table 2), and certainly less likely to use HCT services.
The emergence of condomless sex and self-perceived risk of HIV infection as having a strong positive association with utilization of HCT services was consistent with previous findings in which those who perceived themselves to be at risk of HIV infection  and engaged in risky sexual behaviors  were more likely to utilize the services than their counterparts. This finding supports the notion that undergraduates with higher risk perception and those who had engaged in condomless sex are more likely to require and consequently utilize HCT services.
The first limitation of this study is the cross-sectional design, which limits its ability to confirm causal relationships. Thus, more studies need to be conducted based on a prospective and longitudinal design. Second, a combination of convenience and snowball sampling was applied to recruit students mainly from HUST and thus our sample was not fully representative. It was therefore difficult to generalize the findings to undergraduates from other universities and colleges in mainland China. Third, this study relied mainly on self-reported measurements and might be prone to social desirability bias due to the sensitivity of sexual topics. However, this type of bias might be minimized via anonymous online survey. Fourth, according to the Chinese nominal age system, a person is counted as 1 year old instead of zero year old on the day of his birth and becomes 1 year older each year on the day when the Chinese New Year is celebrated. Thus, he would be 2 years old at the turn of the Chinese New Year, if his birth happens on the last day of the Lunar Year. In other words, the nominal age is usually exaggerated by one to 2 years as compared with the actual age. When asked about their age, some students might report their nominal age instead of their actual age, thus resulting in inaccurate statistics. Given the fact the majority of students come to HUST to pursue a three-, four- or five-year degree at around the age of 18 years, which means that their ages range between 18 and 23 years. However, some university students might upgrade from junior college students or enroll later than the compulsory school attendance, the age range in this study was thus widened to be 18–25 years. Therefore, the respondents in this study were simply asked to select their age from one of four categories (younger than 18 years old = 1; 18–25 years old = 2; 26–29 years old = 3; and 30 years or older = 4) to determine whether they meet our eligibility criteria to be considered for such an analysis. In addition, because Chinese university students in the same grade almost fall into the same category, age in this study was crudely estimated with the students’ grade. Fifth, with the wide use of mobile phones and internet, the web-based survey was easier to participate, especially when the students were allowed to complete during regular class time. Therefore, the participation rate (86.9%) in this study was higher that (75%) reported by Elicker et al. (2010) . However, due to the lack of intrinsic motivation and weak extrinsic incentives such as failure to require participation, low values of extra credit or cash incentives , some students did not participate at all. In order to improve the representativeness of research samples and the quality of the survey research, greater effort should be made to increase students’ interest and enthusiasm by communicating the intrinsic value of scientific research and research participation. Finally, some factors potentially associated with HCT uptake, including individual behaviours such as drug use [7, 8] and having an STD history, HIV status of sexual partners, college characteristics (e.g., vocation school or college) , were not investigated in the present study and merited further research.
Implications of the study
In spite of the above-mentioned limitations, the findings from our study have several implications for the design and implementation of HIV testing programs on college campuses. To the best of our knowledge, this is the first publication that employs the Andersen’s behavioral model as a theoretical framework, together with hierarchical Logistic regression model, to examine equitable distribution of HCT services among a large and diverse undergraduate sample. Our findings suggested that HCT utilization was inequitably distributed and participants who had ever utilized HCT services were mainly those with a higher need for HCT services (i.e., engaging in condomless sex and perceived themselves to be at high risk of acquiring HIV infection) and those with more enabling resources (i.e., being knowledgeable of local AIDS service organization). Furthermore, non-heterosexual men, medical students and non-freshmen and those with lower knowledge of HIV and taking a negative attitude towards HCT services (i.e, expressing unwillingness to utilize HTC service and feeling no necessity of providing HCT on college campuses) were also found to be more likely to use HCT services. In order to increase the utilization rate of HCT services and simultaneously reduce the remaining inequities, three main types of intervention are recommended.
First, target non-heterosexual men, non-freshmen and those with a higher need for HCT services. The tendency for non-heterosexual men, non-freshmen and those with a higher need (i.e., engaging in condomless sex and perceiving themselves to be at higher risk of acquiring HIV) to utilize HCT services would be labeled as equitable and immutable. Therefore, free routine opt-out HIV testing should be immediately implemented among students exhibiting these characteristics , while our long- term goals should be set to recommend such testing option to all undergraduates.
Second, conduct health education: Health education should be conducted to improve undergraduates’ knowledge about HIV transmission and prevention, enhance their willingness to utilize HCT services and raise their awareness of local AIDS service organization. Furthermore, it should be emphasized that HIV risk is dependent on exposure to risky behaviors such as the sharing of HIV-contaminated needles and unprotected sex, rather than participants’ social identities.
Third, improve the availability and accessibility of HIV testing services. Our results indicated that a vast majority of undergraduates expressed willingness to utilize HTC services (83.4%) and recognized the necessity to provide HTC services in the local university (93.4%), and not knowing where to get an HIV test was identified as one of the key barriers for undergraduates to utilization of HTC services. Therefore, continued effort should be needed to recruit and train peer volunteers to provide free HCT services in college campus. However, due to the existence of heterogeneous HIV testing preferences [28,29,30], a variety of HIV testing options should be provided to achieve the ambitious “95–95-95” targets by 2030  and the final goal of three Zeros.