Table 2

Comparison of primary with early latent infection: estimates and CIs for multinomial regression modelling*

Parameter	Estimate	SE (95% CI)	p Value
Intercept	−12.36	142.88 (−292.66 to 267.93)	0.466
Strategic Health Authority
East Midlands (baseline^*)
East of England	12.49	306.01 (−587.83 to 612.82)	0.484
London	0.04	1.13 (−2.18 to 2.26)	0.486
North West	0.65	1.04 (−1.38 to 2.68)	0.266
South Central	10.99	215.44 (−411.65 to 466.64)	0.480
South East Coast	−0.20	1.27 (−2.69 to 2.29)	0.437
South West	0.62	1.12 (−1.58 to 2.81)	0.291
West Midlands	0.26	1.18 (−2.05 to 2.56)	0.413
Yorkshire & The Humber	10.68	290.09 (−558.41 to 579.76)	0.485
Gender
Male (baseline^*)
Female	0.85	1.29 (−1.68 to 3.37)	0.255
Whether born in the UK
UK born (baseline^*)
Non-UK born	0.56	0.37 (−0.16 to 1.29)	0.064
Ethnicity
White
Black	−0.06	0.94 (−1.92 to 1.79)	0.473
Asian	−1.20	0.68 (−2.53 to 0.14)	0.039
Other ethnicity	0.02	0.92 (−1.79 to 1.82)	0.493
Sexual orientation
Heterosexual (baseline^*)
Men who have sex with men	0.31	0.66 (−0.97 to 1.60)	0.317
Reason for attending clinical services
Routine STI screen (baseline^*)
Symptoms	2.34	0.31 (1.74 to 2.94)	<0.001
Campaign	0.26	1.56 (−2.79 to 3.31)	0.433
Partner notification	0.77	0.47 (−0.15 to 1.70)	0.051
Antenatal screening	−14.78	717.42 (−1422.19 to 1392.64)	0.492
Other	−0.32	0.42 (−1.14 to 0.50)	0.224
HIV serostatus
HIV negative (baseline^*)
HIV positive	0.48	0.30 (−0.10 to 1.06)	0.052
Infection acquired through oral sex
No (baseline^*)
Yes	0.12	0.29 (−0.46 to 0.69)	0.346
Partner notification^†
Traceable	−0.01	0.04 (−0.08 to 0.06)	0.399
Untraceable	−0.02	0.01 (−0.03 to 0.00)	0.029
Location
London (baseline^*)
Brighton	−0.76	0.75 (−2.23 to 0.70)	0.153
Manchester	−0.97	0.56 (−2.08 to 0.14)	0.043
Elsewhere UK	0.36	0.56 (−0.74 to 1.46)	0.259
Overseas	−0.55	0.50 (−1.52 to 0.42)	0.134
Commercial sex worker
No (baseline^*)
Yes	0.32	0.76 (−1.17 to 1.80)	0.337
Social network
None (baseline^*)
Sauna	−0.95	0.31 (−1.56 to −0.34)	0.001
Bar	−1.02	0.30 (−1.61 to −0.44)	<0.001
Internet	−1.01	0.31 (−1.61 to −0.41)	0.001
Age
16–19 (baseline^*)
20–24	−1.24	1.23 (−3.66 to 1.17)	0.157
25–34	−1.15	1.21 (−3.52 to 1.23)	0.172
35–44	−0.92	1.23 (−3.32 to 1.49)	0.227
45+	−1.02	1.23 (−3.44 to 1.40)	0.204
Time
Year	0.01	0.07 (−0.13 to 0.15)	0.462

Interpretation: each estimated regression coefficient provides a measure of increased (if positive) or decreased (if negative) likelihood of presenting with primary, relative to early latent infection. For example, an HIV-positive individual would be expected to have a 1.62=exp{0.48} higher OR of presenting with primary syphilis infection (as opposed to early latent) compared with an HIV-negative patient.
↵* Baseline individual: white heterosexual, UK-born HIV-negative male, aged 16–19, who attended genitourinary medicine services in the East Midlands for a routine STI screen, likely to have acquired syphilis in London, but unlikely to have acquired infection through oral sex, not a commercial sex worker and with no stated social/sexual networks.
↵† No baseline is shown for partner notification because it is a discrete variable.
STI, sexually transmitted infection.