HIV and HCV seroincidence, associated factors and drug use in people who inject drugs, SurvUDI network, eastern central Canada, 1995–2020

•HIV seroincidence decreased significantly between 1995 and 2018.•HCV seroincidence decreased significantly (1998–2011), but remains worryingly high since then.•The use of syringes already used by someone else decreased from 43.4 % in 1995 to 12.4 % in 2019.•Cocaine/crack injection decreased while opioids other than heroin injection and daily injection increased. The SurvUDI network is a biobehavioural survey among people who inject drugs (PWID) in Eastern Central Canada. The objectives were to describe HIV and HCV seroincidence trends, associated factors and changes in drug use behaviours. The network was initiated in 1995 and targets hard-to-reach, mostly out-of- treatment PWID. Participants were recruited mostly in harm reduction programs, completed an interviewer-administered questionnaire, provided a sample of gingival exudate for HIV and HCV antibody testing and were identified using an encrypted code allowing identification of multiple participations. Time trends were examined for HIV and HCV seroincidence, selected characteristics and behaviours. Cox proportional hazard regression was used to examine factors associated to HIV and HCV seroincidence. Between January 1995 and March 2020, 15,907 individuals have completed 31,051 questionnaires. HIV seroincidence decreased significantly from 5.0 per 100 person-years (p-y) in 1995 to 0.4 per 100 p-y in 2018. HCV seroincidence also decreased significantly between 1998 and 2011. The use of syringes already used by someone else decreased significantly, from 43.4 % in 1995 to 12.4 % in 2019, as well as the use of equipment other than syringe already used by someone else. Cocaine/crack injection decreased significantly while “opioids other than heroin” injection increased, concomitant to daily injection. Injection with syringes already used by someone else and cocaine as the most often injected drug were significantly associated with HIV seroincidence (1995–2020). Injected opioid other than heroin, injected cocaine/crack, injected 100 or more times in the past month, injected for less than 3 years, injected with syringes or equipment already used by someone else, injected with someone else and reported client sex partners were significantly associated with HCV seroincidence (2004–2020). HIV seroincidence and syringe/equipment sharing behaviour trends are encouraging, but HCV seroincidence remains high.