Table 3

Direct and indirect (mediated) effects of PrEP use on any recent bacterial STI diagnosis via CAS, oral sex (OS) and number of anal sex partners (NSPs); baseline data, Engage cohort study (n=2009)

Predictor	Outcome	β	95% CI	P value
Direct effect
PrEP use	STI	0.04	−0.12 to 0.21	0.62
OS	STI	0.50	0.21 to 0.79	0.001
CAS	STI	0.22	0.07 to 0.37	0.003
PrEP use	OS	0.06	−0.17 to 0.30	0.59
NSPs	OS	0.001	−0.15 to 0.15	0.98
PrEP use	CAS	0.12	0.01 to 0.23	0.03
NSPs	CAS	0.53	0.47 to 0.59	<0.001
PrEP use	NSPs	0.30	0.24 to 0.35	<0.001
Indirect effect
PrEP use–OS	STI	0.033	−0.08 to 0.14	0.57
PrEP use–CAS	STI	0.027	−0.01 to 0.06	0.11
PrEP use–NSPs–OS	STI	0.000	−0.02 to 0.02	0.98
PrEP use–NSPs–CAS	STI	0.035	0.01 to 0.06	0.003
Total effect		0.137	0.03 to −0.24	0.01

The estimated coefficients are standardised coefficients.
CAS, condomless anal sex; PrEP, pre-exposure prophylaxis.