HIV incidence by baseline characteristics
| Characteristic | Participants, n (%) | Total PY | HIV infections | Incidence rate (per 100 PY) | 95% CI | Rate ratio | 95% CI | P value* | |
| Total | 268 (100.0) | 239.3 | 21 | 8.8 | 5.4 to 13.4 | – | – | – | |
| Age (years) | 18–24 | 27 (10.1) | 24.6 | 3 | 12.2 | 2.5 to 35.7 | 1.4 | 0.3 to 4.8 | 0.26 |
| 25–34 | 104 (38.8) | 94.5 | 9 | 9.5 | 4.4 to 18.1 | 1.1 | 0.4 to 2.8 | ||
| 35–49 | 116 (43.3) | 101.0 | 9 | 8.9 | 4.1 to 16.9 | 1.0 | – | ||
| 50+ | 21 (7.8) | 19.1 | 0 | 0 | 0 to 19.3† | 0.4 | 0 to 2.1† | ||
| University degree | No | 101 (38.0) | 90.6 | 6 | 6.6 | 2.4 to 14.4 | 1.0 | – | 0.38 |
| Yes | 165 (62.0) | 146.7 | 15 | 10.2 | 5.7 to 16.9 | 1.5 | 0.6 to 4.3 | ||
| Full-time employment | No | 68 (25.8) | 63.1 | 3 | 4.8 | 1.0 to 13.9 | 1.0 | – | 0.20 |
| Yes | 196 (74.2) | 173.0 | 18 | 10.4 | 6.2 to 16.4 | 2.2 | 0.7 to 9.3 | ||
| Born in UK | No | 107 (40.2) | 96.6 | 9 | 9.3 | 4.3 to 17.7 | 1.0 | – | 0.84 |
| Yes | 159 (59.8) | 140.7 | 12 | 8.5 | 4.4 to 14.9 | 0.9 | 0.4 to 2.3 | ||
| Ethnicity | White | 218 (82.6) | 192.3 | 19 | 9.9 | 5.9 to 15.4 | 1.0 | – | 0.32 |
| Black, Asian and minority | 46 (17.4) | 42.8 | 2 | 4.7 | 0.6 to 16.9 | 0.5 | 0.07 to 1.8 | ||
| London site | No | 81 (30.2) | 71.8 | 6 | 8.4 | 3.1 to 18.2 | 1.0 | – | 0.91 |
| Yes | 187 (69.8) | 167.4 | 15 | 9.0 | 5.0 to 14.8 | 1.1 | 0.4 to 3.0 | ||
| Circumcised | No | 185 (70.1) | 166.2 | 17 | 10.2 | 6.0 to 16.4 | 1.0 | – | 0.30 |
| Yes | 79 (29.9) | 69.8 | 4 | 5.7 | 1.6 to 14.7 | 0.6 | 0.2 to 1.6 | ||
| Relationship status | Living with partner | 73 (27.5) | 66.9 | 6 | 9.0 | 3.3 to 19.5 | 0.9 | 0.3 to 2.3 | 0.32 |
| Not living with partner | 46 (17.4) | 42.1 | 2 | 4.7 | 0.6 to 17.2 | 0.5 | 0.07 to 1.8 | ||
| Single | 146 (55.1) | 127.3 | 13 | 10.2 | 5.4 to 17.5 | 1.0 | – | ||
| High depression score‡ | No | 233 (92.1) | 205.1 | 19 | 9.3 | 5.6 to 14.5 | 1.0 | – | 0.68 |
| Yes | 20 (7.9) | 18.5 | 1 | 5.4 | 0.1 to 30.2 | 0.6 | 0.03 to 3.2 | ||
| Number of HIV tests§ | 0–2 | 91 (35.5) | 82.4 | 5 | 6.1 | 2.0 to 14.2 | 0.7 | 0.2 to 2.1 | 0.13 |
| 3–4 | 122 (47.7) | 106.1 | 9 | 8.5 | 3.9 to 16.1 | 1.0 | – | ||
| 5+ | 43 (16.8) | 38.1 | 6 | 15.7 | 5.8 to 34.2 | 1.9 | 0.6 to 5.3 | ||
| Key STI§ | No | 155 (60.5) | 140.4 | 5 | 3.6 | 1.2 to 8.3 | 1.0 | – | 0.001 |
| Rectal CT/GC or syphilis | 101 (39.5) | 87.0 | 15 | 17.2 | 9.7 to 28.5 | 4.8 | 1.8 to 14.9 | ||
| PEP use§ | No | 159 (63.3) | 142.3 | 11 | 7.7 | 3.9 to 13.8 | 1.0 | – | 0.41 |
| Yes | 92 (36.7) | 80.3 | 9 | 11.2 | 5.1 to 21.3 | 1.4 | 0.6 to 3.6 | ||
| Number of ncRAI partners¶ | 0 | 32 (12.5) | 29.8 | 1 | 3.4 | 0.08 to 18.7 | 1.2 | 0.04 to 16.0 | 0.01 |
| 1 | 78 (30.5) | 72.5 | 2 | 2.8 | 0.3 to 10.0 | 1.0 | – | ||
| 2–4 | 81 (31.6) | 68.7 | 8 | 11.6 | 5.0 to 22.9 | 4.2 | 1.0 to 29.1 | ||
| 5–9 | 35 (13.7) | 30.9 | 5 | 16.2 | 5.3 to 37.8 | 5.9 | 1.2 to 43.7 | ||
| 10+ | 30 (11.7) | 25.7 | 4 | 15.6 | 4.2 to 39.9 | 5.7 | 1.0 to 44.1 | ||
| Drug use associated with chemsex¶** | No | 135 (52.3) | 121.9 | 7 | 5.7 | 2.3 to 11.8 | 1.0 | – | 0.17 |
| Yes | 123 (47.7) | 108.1 | 12 | 11.1 | 5.7 to 19.4 | 1.9 | 0.8 to 5.2 | ||
| Poppers¶ | No | 129 (50.0) | 117.9 | 10 | 8.5 | 4.1 to 15.6 | 1.0 | – | 0.91 |
| Yes | 129 (50.0) | 112.1 | 9 | 8.0 | 3.7 to 15.2 | 0.9 | 0.4 to 2.4 |
Missing data (total, events lost due to missing exposure data) for education (2, 0); employment status (4, 0); born in UK (2, 0); ethnicity (4, 0); circumcised (4, 0); relationship (3, 0); depression (15, 1); number of HIV tests (12, 1); key STI (12, 1); PEP (17, 1); ncRAI (12, 1); chemsex (10, 2); poppers (10, 2).
Quantitative variables were grouped according to clinical considerations.
Key STIs (rectal chlamydia [CT], rectal gonorrhoea [GC] or syphilis).
*P value for trend calculated for ordered categorical variables: ncRAI partners, anal intercourse (AI) partners, age and HIV tests. P value for relationship status compares single versus not living with partner. P value for ethnicity compares white against all other categories combined.
†One sided, 97.5% CI.
‡Defined by the Patient Health Questionnaire-9 (PHQ-9) score, high score ≥10.
§Occurred in 12 months prior to baseline visit.
¶Occurred in the 90 days prior to baseline visit.
**Chemsex-associated drugs defined as the use of methamphetamine, gamma hydroxybutyrate (GHB), mephedrone or ketamine.
PEP, postexposure prophylaxis; PY, person-years; ncRAI, receptive anal intercourse without a condom.