Descriptive characteristics of included studies and participants
| Study | Study design | World region (country) | Study population | No. of participants | Mean or median age | Syphilis prevalence (baseline) | Syphilis confirm test | Length of time between tests for HIV (1≤6 months or 2>6) | Follow-up rate | HIV acquisition | NOS* |
| Prevalent | |||||||||||
| Desai et al 14 | Cohort study | Europe (UK) | MSM | 9309 | 34 | 1.9 | NR | 1 | NR | 2.00 | 7 |
| van Griensven et al 15 | Cohort study | Asia (Thailand) | MSM | 3750 | 26 | 4.7 | RPR & IC | 1 | 76.1% | 5.90 | 7 |
| Riedner et al 26 | Cohort study | Africa (Tanzania) | Other high-risk groups (female bar workers) | 360 | 25 | 17.5 | RPR & TPPA | 1 | 74.5% | NR | 6 |
| Jin et al 16 | Cohort study | Oceania (Australia) | MSM | 5084 | 35 | 2.9 | RPR & TTs | 2 | 81.0% | 0.78 | 6 |
| Ferrer et al 17 | Cohort study | Europe (Spain) | MSM | 2876 | 33 | 0.6 | RPR & TPPA | 2 | 63.4% | 2.40 | 6 |
| Lee and Ho27 | Case-control study | Asia (China-Hong Kong) | Other high-risk groups (STD clinic attendees) | 392 | NR | 3.4 | VDRL & TPPA TPPA | NR | NR | NR | 7 |
| Beymer et al 18 | Case-control study | America (USA) | MSM | 15 107 | 32 | 1.1 | RPR | 2 | 88.3% | 2.18 | 6 |
| Beymer et al 19 | Cohort study | America (USA) | MSM | 2593 | NR | 1.5 | RPR | 1 | 88.1% | 5.40 | 6 |
| Mehta et al 28 | Cohort study | America (USA) | Other high-risk groups (STD clinic attendees) | 13 693 | 25 | 2.8 | NTT & TT | 1 | NR | 0.91 | 6 |
| Guy et al 20 | Cohort study | Oceania (Australia) | MSM | 4488 | 32 | 2.0 | NR | 2 | NR | 1.24 | 8 |
| Ruzagira et al 29 | Cohort study | Africa (Uganda) | Other high-risk groups (HIV discordant couples) | 787 | 36 | 5.2 | RPR & TPHA TPHA | 1 | 97.4% | 4.30 | 8 |
| Su et al 30 | Cohort study | Asia (China) | Other high-risk groups (female sex workers) | 3106 | 27 | 7.4 | RPR & TPPA | 1 | NR | 1.06 | 8 |
| Xu et al 22 | Cohort study | Asia (China) | MSM | 313 | 28 | 5.8 | RPR & TPPA | 1 | 70.1% | 3.50 | 7 |
| Xu et al 23 | Cohort study | Asia (China) | MSM | 122 | 27 | 25.4 | RPR & TPPA | 1 | 56.0% | 5.40 | 7 |
| Yang et al 24 | Cohort study | Asia (China) | MSM | 286 | NR | 12.6 | RPR & TPPA | 1 | 72.0% | 5.12 | 5 |
| Yang et al 25 | Case-control study | Asia (China) | MSM | 303 | 28 | 12.2 | TRUST | NR | NR | NR | 6 |
| Incident | |||||||||||
| Li et al 31 | Cohort study | Asia (China) | MSM | 425 | 26 | 16.9 | RPR & TPPA | 1 | 86.2% | 2.60 | 7 |
| Li et al 32 | Cohort study | Asia (China) | MSM | 593 | 28 | 16.4 | RPR & TPPA | 1 | 86.8% | 8.09 | 8 |
| Braunstein et al 35 | Cohort study | Africa (Rwanda) | Other high-risk groups (female sex workers) | 373 | 24 | 7.3 | RPR & TPPA | 1 | 85.0% | 5.60 | 8 |
| Tang et al 33 | Cohort study | Asia (China) | MSM | 359 | NR | 12.6 | RPR & TPPA | 1 | 51.2% | 3.60 | 6 |
| Wang et al 34 | Cohort study | Asia (China) | MSM | 557 | 36 | 30.9 | TRUST & TPPA TPPA | 1 | 60.3% | 6.78 | 7 |
IC, immunochromatography; MSM, men who have sex with men; NOS, Newcastle-Ottawa Scale (for assessing the quality of non-randomised studies in meta-analyses); NR, not reported; NTT, non-treponemal test; RPR, rapid plasma regain; TPHA, Treponema pallidum haemagglutination assay; TPPA, T. pallidum passive particle agglutination; TRUST, toluidine red unheated serum test; TT, treponemal test.