Table 3 Crude and adjusted odds ratios and confidence limits of association between HIV prevalence, and city by year of cross sectional study and years since first injection. Young heroin users who had ever injected in two cross sectional studies carried out in Barcelona, Madrid and Seville in 1995 and 2001–03.

Years since first injection	City	1995		2001–03
		Crude OR	Adjusted OR	Crude OR	Adjusted OR
		(95% CI)	(95% CI)	(95% CI)	(95% CI)
⩽5	Barcelona	1	1	1	1
	Madrid	0.6 (0.2 to 2.0)	0.9 (0.1 to 6.5)	1.0 (0.5 to 2.0)	1.3 (0.5 to 3.5)
	Seville	0.7 (0.3 to 1.6)	0.2 (0.0 to 1.2)	0.9 (0.2 to 3.2)	0.7 (0.1 to 4.3)
>5	Barcelona	1	1	1	1
	Madrid	0.8 (0.4 to 1.3)	1.2 (0.5 to 2.8)	2.3 (1.4 to 3.7)	3.1 (1.5 to 6.2)
	Seville	1 (0.5 to 1.8)	1.3 (0.6 to 2.3)	1.0 (0.5 to 2.3)	1.5 (0.5 to 4.8)

Adjusted for the following variables (included and retained in the model): sex, employment status, educational level, prison, first drug injected, drug most frequently injected, sexual relation without condoms, sexual relations for money, injected in past 30 days, ever borrowed, and borrowed in past 30 days.