Prevalence and proportion of asymptomatic NG and/or CT infections
Between April 2018 and May 2018, 8,309 eligible individuals were invited to participate in this study. Of these, 7070 participants completed the questionnaire and provided the urine specimen for the molecular detection of NG and CT, so the survey response rate was 85.1%. In total, 769 (10.9%) participants screened positive for STIs (NG, CT, or both): 182 (2.6%) participants were positive for NG, 648 (9.2%) for CT, and 61 (0.8%) were co-infected with NG/CT. By symptomatology, urogenital NG was detected in 165 of 4199 symptomatic participants (3.9%) and in 17 of 2871 asymptomatic participants (0.6%); urogenital CT was detected in 441 of 4199 symptomatic participants (10.5%) and in 207 of 2871 asymptomatic participants (7.2%). The proportion of participants without symptoms was 2871/7070 (40.6%): 1120 (39.0%) males and 1751 (61.0%) females. Among males reporting no symptoms, the prevalence of NG and CT was 0.9% and 6.2%, respectively. Among females reporting no symptoms, the prevalence of NG and CT was 0.4% and 7.9%, respectively (Fig. 1). The proportion of asymptomatic urethral NG among males with urethral NG was 7.2%; for females, it was 16.3%. The proportion of asymptomatic urethral CT among males with urethral CT was 28.3%; for females, it was 34.2% (Table 1).
Table 1
Sexually Transmitted Infections (STIs) Detected Stratified by Sex and Presence of STI Symptoms
| STIs Detected Among Male, No. (%) | | STIs Detected Among Female, No. (%) |
| |
Type of STI | Total | Asymptomatic | | Total | Asymptomatic |
Gonorrhea | 139 (36.3) | 10 (7.2) | | 43 (9.6) | 7 (16.3) |
Chlamydia | 244 (63.7) | 69 (28.3) | | 404 (90.4) | 138 (34.2) |
Total | 383 (100) | 79 (20.6) | | 447 (100) | 145 (32.4) |
Characteristics of asymptomatic male participants
Of 1120 asymptomatic male participants included in this analysis, 60.0% were more than 30 years old; 54.1% had no children; 58.1% lived with their spouse; 73.7% were immigrants (unregistered residents of Shenzhen); 92.6% lived in Shenzhen for more than one year; 29.8% were workers and 50.9% had education at the senior high school level or higher (Table 2).
Table 2
Characteristics of asymptomatic male participants in Shenzhen, China
| | Asymptomatic Male Participants | |
| | No. Total (%) N = 1120 | No. Negative cases (%) N = 1046 | No. Positive cases (%) N = 74 | P value |
Variables | | |
Age, y | ≤ 30 | 448 (40.0) | 408 (39.0) | 40 (54.1) | 0.011 |
| > 30 | 672 (60.0) | 638 (61.0) | 34 (45.9) | |
Children | NO | 606 (54.1) | 568 (54.3) | 38 (51.4) | 0.788 |
| Yes | 510 (45.5) | 476 (45.5) | 34 (45.9) | |
Living arrangements status | Living alone | 144 (12.9) | 136 (13.0) | 8 (10.8) | 0.078 |
| Living with spouse | 651 (58.1) | 615 (58.8) | 36 (48.6) | |
Residence status | Local residents | 295 (26.3) | 279 (26.7) | 16 (21.6) | 0.340 |
| Migrants | 825 (73.7) | 767 (73.3) | 58 (78.4) | |
Local residence time | 0–12 months | 83 (7.4) | 77 (7.4) | 6 (8.1) | 0.813 |
| Over 1 year | 1037 (92.6) | 969 (92.6) | 68 (91.9) | |
Occupation | Staff | 330 (29.5) | 318 (30.4) | 12 (16.2) | 0.013 |
| Commercial services | 304 (27.1) | 276 (26.4) | 28 (37.8) | |
| Housework or unemployed | 12 (1.1) | 11 (1.0) | 1 (1.4) | |
| Worker | 334 (29.8) | 316 (30.2) | 18 (24.3) | |
Highest educational level | Lower than senior high school | 550 (49.1) | 508 (48.6) | 42 (56.8) | 0.175 |
| Senior high school and above | 570 (50.9) | 538 (51.4) | 32 (43.2) | |
Clinical settings | Dermatological department | 362 (32.3) | 344 (32.9) | 18 (24.3) | < 0.001 |
| Urological department | 536 (47.9) | 486 (46.5) | 50 (67.6) | |
| Family planning department | 220 (19.6) | 215 (20.6) | 5 (6.8) | |
Insurance | Private/Medicaid | 724 (64.6) | 682 (65.2) | 42 (56.8) | 0.144 |
| Uninsured | 396 (35.4) | 364 (34.8) | 32 (43.2) | |
Sex with anonymous partner last 3 months | Yes | 554 (49.5) | 511 (48.9) | 43 (58.1) | 0.126 |
| No | 566 (50.5) | 535 (51.1) | 31 (41.9) | |
History of STI infection | No | 980 (87.5) | 916 (87.6) | 64 (86.5) | 0.361 |
| Yes | 63 (5.7) | 57 (5.4) | 6 (8.1) | |
History of STI test | No | 1021 (91.2) | 952 (91.0) | 69 (93.2) | 0.515 |
| Yes | 99 (8.8) | 94 (9.0) | 5 (6.8) | |
STI-related knowledge | Low | 869 (77.6) | 813 (77.7) | 56 (75.7) | 0.683 |
| High | 251 (22.4) | 233 (22.3) | 18 (24.3) | |
Partner notification | No | 92 (8.2) | 86 (8.2) | 6 (8.1) | 0.933 |
| Yes | 1007 (89.9) | 939 (89.8) | 68 (91.9) | |
Because of the low prevalence of NG in our study, we decided to integrate the number of cases of NG and CT for final analyses. Overall, the prevalence of STIs among males reporting no symptoms was 74/1120 (6.6%). When compared with asymptomatic males not infected with STIs, there were more asymptomatic males infected with STIs aged less than 30 years (54.1% vs 39.0%), being employed in commercial service work (37.8% vs 26.4%) and being recruited through the urological department (67.6% vs 46.5%) (Table 2).
Factors associated with asymptomatic NG and/or CT infections among male participants
Based on the univariate linear regression results, the following variables: age, occupation, highest educational level, clinical settings, insurance and sex with anonymous partner last 3 months were selected for the multivariate analysis. Risk factors associated with urethral STIs among male participants with having no symptoms included males aged less than 30 years (OR, 1.75; 95% CI, 1.07–2.84), being employed in commercial service work (2.69; 1.33–5.45) and being recruited through urological department (vs dermatological department, 2.18; 1.24–3.83) (Table 3).
Table 3
Factors associated with asymptomatic NG and/or CT infections among male participants
Variables | Univariate analysis | Multivariate analysis |
OR (95%CI) | P value | aOR (95%CI) | P value |
Age, y | | | | |
> 30 | 1 | | 1 | |
≤ 30 | 1.84 (1.15–2.96) | 0.012 | 1.745 (1.07–2.84) | 0.025 |
Occupation | | | | |
Staff | 1 | | 1 | |
Commercial services | 2.69 (1.34–5.39) | 0.005 | 2.69 (1.33–5.45) | 0.006 |
Housework or unemployed | 2.41 (0.29–20.21) | 0.418 | ― | ― |
Worker | 1.51 (0.72–3.19) | 0.280 | ― | ― |
Highest educational level | | | | |
Lower than senior high school | 1 | | 1 | |
Senior high school and above | 0.72 (0.45–1.16) | 0.175 | 0.95 (0.74–1.21) | 0.672 |
Clinical settings | | | | |
Dermatological department | 1 | | 1 | |
Urological department | 1.97 (1.13–3.43) | 0.017 | 2.18 (1.24–3.83) | 0.007 |
Family planning department | 0.44 (0.164–1.22) | 0.144 | 0.50 (0.18–1.38) | 0.179 |
Insurance | | | | |
Private/Medicaid | 1 | | 1 | |
Uninsured | 1.43 (0.89–2.30) | 0.144 | 0.96 (0.55–1.66) | 0.874 |
Sex with anonymous partner last 3 months | | | | |
Yes | 1 | | 1 | |
No | 0.69 (0.43–1.11) | 0.126 | 0.85 (0.51–1.42) | 0.526 |
Characteristics of asymptomatic female participants
Of 1751 asymptomatic female participants included in this analysis, 59.0% were more than 30 years old; 64.4% had children; 75.7% lived with their spouse; 70.0% were immigrants (unregistered residents of Shenzhen); 90.6% lived in Shenzhen for more than one year; 28.1% were staffs and 70.5% had education at the senior high school level or higher (Table 4).
Table 4
Characteristics of asymptomatic female participants
| | Asymptomatic Female Participants | |
| | No. Total (%) N = 1751 | No. Negative cases (%) N = 1609 | No. Positive cases (%) N = 142 | P value |
Variables | | |
Age, y | ≤ 30 | 718 (41.0) | 638 (39.7) | 80 (56.3) | < 0.001 |
| > 30 | 1033 (59.0) | 971 (60.3) | 62 (43.7) | |
Children | NO | 609 (34.8) | 546 (33.9) | 63 (44.4) | 0.026 |
| Yes | 1128 (64.4) | 1051 (65.3) | 77 (54.2) | |
Living arrangements status | Living alone | 114 (6.5) | 104 (6.5) | 10 (7.0) | 0.250 |
| Living with spouse | 1325 (75.7) | 1245 (77.4) | 80 (56.3) | |
Residence status | Local residents | 525 (30.0) | 498 (41.0) | 27 (19.0) | 0.003 |
| Migrants | 1226 (70.0) | 1111 (69.0) | 115 (81.0) | |
Local residence time | 0–12 months | 165 (9.4) | 147 (9.1) | 18 (12.7) | 0.166 |
| Over 1 year | 1586 (90.6) | 1462 (90.9) | 124 (87.3) | |
Occupation | Staff | 492 (28.1) | 460 (28.6) | 32 (22.5) | 0.013 |
| Commercial services | 336 (19.2) | 299 (18.6) | 37 (26.1) | |
| Housework or unemployed | 375 (21.4) | 349 (21.7) | 26 (18.3) | |
| Worker | 279 (15.9) | 247 (15.4) | 32 (22.5) | |
Highest educational level | Lower than senior high school | 516 (29.5) | 465 (28.9) | 51 (35.9) | 0.320 |
| Senior high school and above | 1235 (70.5) | 1144 (71.1) | 91 (64.1) | |
Clinical settings | dermatological department | 75 (4.3) | 62 (3.9) | 13 (9.2) | 0.026 |
| gynecological department | 1367 (78.1) | 1258 (78.2) | 109 (76.8) | |
| Family planning department | 276 (15.8) | 259 (16.1) | 17 (12.0) | |
Insurance | Private/Medicaid | 1140 (65.1) | 1060 (65.9) | 80 (56.3) | 0.022 |
| Uninsured | 611 (34.9) | 549 (34.1) | 62 (43.7) | |
Sex with anonymous partner last 3 months | Yes | 463 (26.4) | 422 (26.2) | 41 (28.9) | 0.493 |
| No | 1288 (73.6) | 1187 (73.8) | 101 (71.1) | |
History of STI infection | No | 1497 (85.5) | 1374 (85.4) | 123 (86.6) | 0.871 |
| Yes | 76 (4.3) | 71 (4.4) | 5 (35.5) | |
History of STI test | No | 1599 (91.3) | 1463 (90.9) | 136 (95.8) | 0.049 |
| Yes | 152 (8.7) | 146 (9.1) | 6 (4.2) | |
STI-related knowledge | Low | 1407 (80.4) | 1282 (79.7) | 125 (88.0) | 0.016 |
| High | 344 (19.6) | 327 (20.3) | 17 (12.0) | |
Partner notification | No | 88 (5.0) | 77 (4.8) | 11 (7.7) | 0.165 |
| Yes | 1594 (91.0) | 1466 (91.1) | 128 (90.1) | |
Overall, the prevalence of STIs among females reporting no symptoms was 142/1751 (8.1%). When compared with asymptomatic females not infected with STIs, there were more asymptomatic females infected with STIs aged less than 30 years (56.3% vs 39.7%), who had no children (44.4% vs 33.9%), who were migrants (81.0% vs 69.0), and uninsured (43.7% vs 34.1%). In addition, most females with STIs were employed in commercial service work (26.1% vs 18.6%), recruited through dermatological department (9.2% vs 3.9%), having no history of STI testing (95.8% vs 90.9%) and having low STI-related knowledge (88.0% vs 79.7%) (Table 4).
Factors associated with asymptomatic NG and/or CT infections among female participants
Based on the univariate linear regression results, the following variables: age, children, residence status, local residence time, occupation, clinical settings, insurance, history of STI test, STI-related knowledge and partner notification were selected for the multivariate analysis. Risk factors associated with urethral STIs among female participants with having no symptoms included females aged less than 30 years (OR, 1.80; 95% CI, 1.25–2.58) and being recruited through the dermatological department (vs gynecological department, 2.83; 1.46–5.46) (Table 5).
Table 5
Factors associated with asymptomatic NG and/or CT infections among female participants
Variables | Univariate analysis | Multivariate analysis |
OR (95%CI) | P value | aOR (95%CI) | P value |
Age, y | | | | |
> 30 | 1 | | 1 | |
≤ 30 | 1.96 (1.39–2.78) | 0.000 | 1.80 (1.25–2.58) | 0.001 |
Children | | | | |
NO | 1 | | 1 | |
Yes | 0.64 (0.45–0.90) | 0.011 | 0.77 (0.50–1.19) | 0.238 |
Residence status | | | | |
Local residents | 1 | | 1 | |
Migrants | 1.91 (1.24–2.94) | 0.003 | 1.48 (0.93–2.34) | 0.100 |
Local residence time | | | | |
0–12 months | 1 | | 1 | |
Over 1 year | 0.83 (0.64–1.08) | 0.168 | 0.91 (0.69–1.19) | 0.494 |
Occupation | | |
Staff | 1 | | | |
Commercial services | 1.78 (1.08–2.92) | 0.023 | 1.48 (0.88–2.48) | 0.140 |
Housework or unemployed | 1.07 (0.63–1.83) | 0.802 | ― | ― |
Worker | 1.86 (1.11–3.11) | 0.018 | 1.50 (0.87–2.57) | 0.141 |
Clinical settings | | | | |
Gynecological department | 1 | | 1 | |
Dermatological department | 2.42 (1.29–4.54) | 0.006 | 2.83 (1.46–5.46) | 0.002 |
Family planning department | 0.76 (0.45–1.29) | 0.303 | ― | ― |
Insurance | | | | |
Private/Medicaid | 1 | | 1 | |
Uninsured | 1.50 (1.06–2.12) | 0.023 | 1.07 (0.72–1.60) | 0.730 |
History of STI test | | | | |
No | 1 | | 1 | |
Yes | 0.44 (0.19–1.02) | 0.055 | 0.53 (0.23–1.26) | 0.154 |
STI-related knowledge | | | | |
Low | 1 | | 1 | |
High | 0.53 (0.32–0.90) | 0.018 | 0.59 (0.34–1.02) | 0.058 |
Partner notification | | | | |
No | 1 | | 1 | |
Yes | 0.59 (0.34–1.02) | 0.057 | 0.76 (0.39–1.51) | 0.436 |