Participants and settings

Zhejiang Province is located in the Yangtze River Delta region on the southeast coast of China. It is between 118°01’~123°10’ east longitude and 27°02’~31°11’ north latitude. In 2019, the Zhejiang Provincial Department of Education and the Zhejiang Provincial Health Commission jointly issued a document requiring schools to include AIDS education in their health education plans, organize the implementation of preventive education, and encourage college students to take the initiative to receive voluntary AIDS counseling and testing services. A survey was conducted among students attending 13 colleges in 11 districts and cities in Zhejiang Province from October to November 2018, including 3 colleges/universities in Hangzhou and 1 college/university each in another 10 cities. The types of universities were chosen as university or vocational technical college, and the selection of universities was as recommended by the local CDC. A total of 31,674 students were surveyed, of which 14,320 were male students. The inclusion criterion for the study subjects resulting in the selection of 2734 male students was that they self-reported having sex, accounting for 19.1% of the total number of male students. This study complies with the Declaration of Helsinki, which was reviewed and approved by the Ethics Committee of the Zhejiang Provincial Center for Disease Control and Prevention as well, and for which the batch number is 2018–036. All survey participants provided signed informed consent.

Study variables and measurements

The questionnaire was formulated after reading the domestic and foreign literature, discussions with the research team, and conducting preliminary surveys of students. The main content of the questionnaire included general population sociological characteristics, knowledge of HIV and STDs, the occurrence of sexual behaviors, and the acceptance of interventions. There are 7 items about HIV/AIDS prevention and treatment knowledge, where answering 5 or more items correctly was defined as having HIV/AIDS prevention and treatment knowledge. These 7 items were as follows: Whether knowing AIDS is an incurable and serious infectious disease? (Item 1); Whether the main mode of HIV transmission among young Chinese students is male homosexual sex?(Item 2); Whether it can be judged by appearance that a person is infected with HIV?(Item 3); Whether daily life and contact spread HIV?(Item 4); Whether the correct use of condoms reduces the risk of infection and transmission of HIV?(Item 5); Whether there is a need to proactively seek HIV counseling and testing after high-risk sex?(Item 6); Whether knowing that the local government provides free antiretroviral treatment for people living with HIV/AIDS? (Item 7). Casual sexual behaviors means whether the participants ever had temporary sex (such as one-night stand / dating, sex with ordinary acquaintances) in the past year.

Data collection

Using the stratified cluster sampling method, a random number table was used to select 3 departments in each university, and then classes were selected from each department by grade. An electronic questionnaire was generated with the web link or QR code, and was distributed to each participant by WeChat. The investigators were composed of tutors who were responsible for tutoring these classes, and were trained by the research team before the investigation.

Quality control

Using the cross-sectional survey method, the students were organized by the teachers to fill in the online electronic questionnaires. Students who were currently not at school had the questionnaire network link sent to them, and they filled out the survey after being given the instructions. The measurement of condom use effectiveness included three questions as follows: Do you have confidence in discussing condom use with your partner before having sex? When the partner refuses to use a condom or does not carry a condom, is there any confidence not to have sex? Do you have the confidence to prepare condoms in advance before having sex? There were 5 options for answering these three questions: very confident, somewhat confident, confident, unconfident, and very unconfident, assigned scores of 3, 2, 1, 0, and −1, respectively. The measurement scores were divided into three groups, namely, unconfident, confident, and very confident, according to 1 point or less, 2–5 points and 6–9 points, respectively. The measured Cronbach’s alpha coefficient in this study was 0.852.

The investigators consisted of professionals from the local Center for Disease Control and Prevention and counselors from the middle classes selected by the universities. After unified training, a unified questionnaire was used to conduct an anonymous survey. The investigator explained the purpose, significance, investigation method, and privacy protection policy of the research before the survey and placed these descriptions in the opening remarks of the questionnaire. The research subjects were told that the purpose of the survey was to formulate strategies for protecting students from HIV and other STDs. The survey analyzed only data from this group, excluding personal data.

Statistical analysis

SPSS version 21.0 software (IBM, Armonk, NY, United States) were used for data analysis. Some variables such as age, grade, hometown, household registration, family relationship, and sexual behavior characteristics are expressed by the composition rate. The χ² test was used to compare the demographic characteristics of the male college students with different sexual behaviors. The measurement data are expressed by the mean ± standard deviation. Whether the participants engaged in casual sexual behavior was the dependent variable. Independent variables included demographic characteristics, sexual attitudes, acceptance of interventions, and self-efficacy of safe sexual behaviors. The single-factor logistic regression method was used to analyze the factors influencing casual sexual behavior among male college students. Variables with P<0.1 in the univariate analysis and demographic characteristics such as age, grade and hometown were included as independent variables in the multivariate logistic regression analysis model. P<0.05 was considered statistically significant.

General characteristics

Among the 2734 subjects, 595 engaged in casual sexual behavior, accounting for 21.8%; 2139 engaged in no casual sexual behavior, accounting for 78.2%. Their ages were between 16 and 28 years old, with that of the casual sexual behavior group being 20.10±1.42 and that of the without casual sexual behavior group being 20.23±1.40. There were no significant differences in age, household registration, or family relationship between the two groups (P>0.05), but significant differences were found between the two groups for grade and hometown (P<0.05). The statistical analysis results are shown in Table 1.

Table 1

Demographic characteristics of 2734 male college students.

Variables	Casual sexual behavior group (n = 595)		Without casual sexual behavior group (n = 2139)		x2	P
	n	%	n	%
Age (years)
≤19	196	32.9	631	29.5	3.404	0.182
20–21	309	51.9	1135	53.1
≥22	90	15.2	373	17.4
Grades
Freshman	121	20.3	405	19.0	21.072	<0.001
Sophomore	200	33.6	642	30.0
Junior	206	34.6	674	31.5
Senior	68	11.5	418	19.5
Household registration*
Zhejiang Province	437	73.6	1492	69.8	3.262	0.075
Other Provinces	157	26.4	647	30.2
Hometown
City	166	27.9	518	24.2	14.821	0.001
Town	109	18.3	292	13.7
Rural area	320	53.8	1329	62.1
Family relationship
Harmonious	470	79.0	1639	76.6	1.479	0.224
General/disharmonious	125	21.0	500	23.4

*There is missing data for one participant.

Awareness rate of HIV prevention knowledge

Among the 2734 male college students, 2328 answered 5 questions correctly, accounting for 85.1%. Among them, the rate of correctly answering "Item 2" was higher in the casual sex group (49.41%) than in the noncasual sex group (43.43%), and there was a significant difference (P<0.05). The rate of correctly answering the other 6 questions in the two groups was between 63.19% and 97.34%. The rate of correctly answering "Item 3", "Item 4", "Item 5", and "Item 6" in the noncasual sexual behavior group was higher than that in the casual sexual behavior group, and the difference between the two groups was significant (P<0.05). The statistical analysis results are shown in Table 2.

Table 2

HIV/AIDS awareness rate among 2734 male college students.

Variables	Casual sexual behavior group (n = 595)						Without casual sexual behavior group (n = 2139)						x2	P
	Correct	%	Wrong	%	Don’t know	%	Correct	%	Wrong	%	Don’t know	%
Item 1	462	77.65	105	17.65	28	4.7	1608	75.18	469	21.92	62	2.9	9.055	0.011
Item 2	294	49.41	240	40.34	61	10.25	929	43.43	963	45.02	247	11.55	6.737	0.034
Item 3	444	74.62	87	14.62	64	10.76	1894	88.55	101	4.72	144	6.73	86.81	<0.001
Item 4	457	76.81	104	17.48	34	5.71	1930	90.23	129	6.03	80	3.74	85.55	<0.001
Item 5	548	92.1	25	4.2	22	3.7	2082	97.34	30	1.4	27	1.26	34.86	<0.001
Item 6	540	90.76	30	5.04	25	4.2	2056	96.12	44	2.06	39	1.82	27.98	<0.001
Item 7	376	63.19	104	17.48	115	19.33	1363	63.72	334	15.61	442	20.67	1.438	0.487
Answering 5 or more items correctly	477	80.17	118	19.83			1851	86.54	288	13.46			14.93	<0.001

Analysis of factors influencing casual sexual behavior

In the univariate analysis, the participants who had received the school’s HIV test promotion in the last year (Crude OR = 1.48), those who had received the self-assessment of AIDS risk conducted by the school (Crude OR = 1.98), those who were aware that the school had HIV self-test kits available (Crude OR = 3.04), those who had accepted a one-night stand (Crude OR = 4.29), those who had accepted commercial sex (Crude OR = 3.82), those who were MSM (Crude OR = 3.30), those who had heard of voluntary counseling and testing for AIDS (Crude OR = 1.49), and those who had accepted HIV voluntary counseling and testing services in the past year (Crude OR = 2.26) were more likely to engage in casual sexual behaviors. The participants who knew that the CDC provides HIV testing services (Crude OR = 0.63) and knew about HIV/AIDS prevention and treatment (Crude OR = 0.63) were more likely not to have casual sex. The statistical analysis results are shown in Table 3.

Table 3

Analysis of factors influencing casual sexual behavior among male college students.

Variables	Casual sexual behavior group (n = 595)		Without casual sexual behavior group (n = 2139)		Univariate analysis		Multivariate analysis
	n	%	n	%	Crude OR (95%CI)	P	Ajusted OR (95%CI)	P
Age (years)
≤19	196	32.9	631	29.5	1.0		1.0
20–21	309	51.9	1135	53.1	1.14(0.93–1.40)	0.205	1.11(0.84–1.47)	0.481
≥22	90	19.4	373	17.4	1.29(0.97–1.70)	0.078	1.33(0.90–1.95)	0.152
Hometown
City	166	27.9	518	24.2	1.0		1.0
Town	109	18.3	292	13.7	0.75(0.61–0.93)	0.009	1.27(0.93–1.73)	0.131
Rural area	320	53.8	1329	62.1	0.65(0.50–0.83)	0.001	0.86(0.68–1.09)	0.201
Grades
Freshman	121	20.3	405	18.9	1.0		1.0
Sophomore	200	33.6	642	30	1.04(0.81–1.35)	0.75	0.87(0.65–1.18)	0.371
Junior	206	34.6	674	31.5	1.02(0.79–1.32)	0.862	0.81(0.57–1.15)	0.24
Senior	68	11.4	418	19.5	0.55(0.39–0.76)	<0.001	0.46(0.30–0.71)	<0.001
Whether had known about HIV/AIDS prevention and treatment
No	118	19.8	288	13.5	1.0		1.0
Yes	477	80.2	1851	86.5	0.63(0.50–0.80)	<0.001	0.66 (0.51–0.86)	<0.001
Whether received a school lecture on HIV/AIDS in the past year
No	178	29.9	713	33.3	1.0		——
Yes	417	70.1	1426	66.7	1.17(0.96–1.43)	0.116
Whether had received the school’s HIV test promotion in the last year
No	185	31.1	855	40	1.0		1.0
Yes	410	68.9	1284	60	1.48(1.22–1.79)	<0.001	1.09(0.86–1.39)	0.465
Whether had received the self-assessment of AIDS risk conducted by the school
No	296	49.7	1417	66.2	1.0		1.0
Yes	299	50.3	722	33.8	1.98(1.65–2.38)	<0.001	1.45(1.14–1.84)	0.003
Whether had awared that the school had HIV self-test kits available
No	392	65.9	1828	85.5	1.0		1.0
Yes	203	34.1	311	14.5	3.04(2.47–3.75)	<0.001	2.02(1.56–2.62)	<0.001
Whether had accepted a one-night stand
No	135	22.7	1192	55.7	1.0		1.0
Yes	460	77.3	947	44.3	4.29(3.48–5.29)	<0.001	2.82(2.18–3.66)	<0.001
Whether had accepted commercial sex
No	260	43.7	1599	74.8	1.0		1.0
Yes	335	56.3	540	25.2	3.82(3.16–4.61)	<0.001	1.95(1.53–2.48)	<0.001
Whether had accepted homosexual sex between MSM
No	456	76.6	1958	91.5	1.0		1.0
Yes	139	23.4	181	8.5	3.30(2.59–4.21)	<0.001	1.81(1.37–2.39)	<0.001
Whether had heard of voluntary counseling and testing for AIDS
No	238	40	1067	49.9	1.0		1.0
Yes	357	60	1072	50.1	1.49(1.24–1.80)	<0.001	1.14(0.90–1.43)	0.276
Whether had known that the CDC provides HIV testing services
No	85	14.3	202	9.4	1.0		1.0
Yes	510	85.7	1937	90.6	0.63(0.48–0.82)	0.001	0.56(0.41–0.77)	<0.001
Whether had accepted HIV voluntary counseling and testing services in the past year
No	534	89.7	2036	95.2	1.0		1.0
Yes	61	10.3	103	4.8	2.26(1.62–3.14)	<0.001	1.34(0.91–1.97)	0.14
Condom use self-efficacy measurement*
No confidence	26	4.7	90	4.3	1.0		——
Have confidence	147	26.5	724	34.9	0.70(0.44–1.13)	0.142
Very confident	381	68.8	1260	60.8	1.05(0.67–1.64)	0.843
Whether had sex with a regular partner in the past year*
Yes	400	70.4	1381	67.4	1.0		——
No	168	29.6	668	32.6	1.15(0.94–1.41)	0.172
Whether had condom use during sex with a fixed partner*
Never use	117	29.3	67	4.9	1.0		——
Sometimes/frequently used	154	38.6	510	37.2	0.17(0.12–0.25)	<0.001
Always use	128	32.1	795	57.9	0.09(0.07–0.13)	<0.001

*There is missing data.

In the multivariate analysis, there were no significant differences in the two demographic characteristics of age and hometown (P>0.05). The participants who had received a self-assessment of HIV risk conducted by the school (Ajusted OR = 1.45, 95% CI = 1.14–1.84), those who were aware HIV self-test kits were available at school (Ajusted OR = 2.02, 95% CI = 1.56–2.62), those who had accepted a one-night stand (Ajusted OR = 2.82, 95% CI = 2.18–3.66), those who had accepted commercial sex (Ajusted OR = 1.95, 95% CI = 1.53–2.48), and those who were MSM (Ajusted OR = 1.81, 95% CI = 1.37–2.39) were more inclined to have casual sex. The participants who were seniors (Ajusted OR = 0.46, 95% CI = 0.30–0.71), those who had awareness of HIV/AIDS prevention and treatment (Ajusted OR = 0.66, 95% CI = 0.51–0.86), and those who knew that the CDC provides HIV testing services (Ajusted OR = 0.56, 95% CI = 0.41–0.77) were not inclined to engage in casual sexual behaviors.