Table 3.

Modification of the effect of chemsex at baseline on time to first STI diagnosis among pre-exposure prophylaxis (PrEP) users by age, education or income

	No chemsex reported		Chemsex reported		HR (95% CI) for chemsex within strata
	n	HR	n	HR
Effect modification by age
18–35	750	1.57 (1.17 to 2.10)	290	2.69 (1.96 to 3.68)	1.71 (1.36 to 2.15)
36–50	575	1.30 (0.97 to 1.74)	164	1.00 (0.67 to 1.48)	0.77 (0.55 to 1.07)
>50	254	1.00 (ref.)	53	1.53 (0.90 to 2.60)	1.53 (0.90 to 2.60)
Effect modification by education
Secondary or under	230	1.00 (ref.)	87	1.61 (0.98 to 2.64)	1.61 (0.98 to 2.64)
Post-secondary	1349	1.16 (0.81 to 1.65)	420	1.47 (1.03 to 2.11)	1.27 (1.04 to 1.55)
Effect modification by income ($C)
≤35 000	449	1.00 (ref.)	162	1.71 (1.23 to 2.36)	1.71 (1.23 to 2.36)
35 001–75 000	668	1.01 (0.76 to 1.34)	238	1.26 (0.92 to 1.71)	1.25 (0.96 to 1.63)
>75 000	462	1.18 (0.88 to 1.57)	107	1.24 (0.82 to 1.86)	1.05 (0.72 to 1.54)

Created by the authors.

Models adjusted for age, education, income, PrEP regimen at baseline and year of entry into the cohort (all categorical).

For education and income, the group size n in each cell is the average group size from the imputed datasets.