Independent associations with HIV-1 infection (multifactorial analysis) and associated population attributable fractions among 347 male injecting drug users in Bangkok, Thailand Characteristic Adjusted odds ratio (95% CI) Adjusted population attributable fraction (95% CI) Years of injecting (per year) 1.0 (0.99 to 1.1) 0.104 (0.09 to 0.26) Used methamphetamine one month before incarceration (injected v no use or not an intravenous drug user) 3.3 (1.01 to 10.7) 0.025 (0.004 to 0.05) Shared needles in holding cell (yes v no) 1.9 (1.2 to 3.0) 0.111 (0.02 to 0.19) Tattooed in prison (yes v no) 2.1 (1.3 to 3.4) 0.171 (0.06 to 0.27) Borrowed needles one month after incarceration (yes v no) 2.5 (1.3 to 4.4) 0.086 (0.03 to 0.14)