A prospective cohort study of risk behaviours, retention and loss to follow-up over 5 years among women and men in a needle exchange program in Stockholm, Sweden

•Injection and sexual risk behaviours varied between women and men subgroups.•Intimate relationships display high-risk behaviours, linked to HIV and HCV-infection.•Women were more likely than men to remain in the needle exchange program over time.•Determinants associated with being lost to follow-up differed between men and women. Needle exchange programs (NEP) are important in reducing risk behaviours among people who inject drugs (PWID), also exposed to HIV and hepatitis C (HCV) through injecting drug use (IDU). Women (WWID) compared to men who inject drugs (MWID), are particularly vulnerable with complex needs, however less is known about their risk determinants and NEP outcomes. In an open prospective NEP cohort, 697 WWID and 2122 MWID were followed, 2013–2018. Self-reported socio/drug-related determinants for receptive injection (needle/syringe and paraphernalia) and sexual risk behaviours at enrolment, lost to follow-up (LTFU) and probability of retention, were assessed for both groups. Multivariable logistic regression (adjusted odds ratios, aOR) for enrolment and Poisson regression (adjusted incidence rate ratios, aIRR) for LTFU, were used. Cumulative NEP-retention probability was analysed using a six- and 12-month scenario. At NEP enrolment, injection risk behaviours among WWID were associated with: younger age; homelessness; amphetamine-IDU; non-participation in opioid substitution therapy (OST); history of custody and among MWID: lower education level; cohabitation; homelessness, being a tenant; amphetamine-IDU; non-participation in OST; history of being sectioned, HIV-negative and HCV-positive. Condomless sex among WWID was associated with: younger age; lower education-level; cohabitation; having a partner; amphetamine-IDU; non-participation in OST; being HIV-negative and HCV-positive and among MWID: younger age; married; cohabitation; having a partner; amphetamine-IDU; non-participation in OST; history of custody, prison and being HIV-negative. WWID had higher NEP-retention levels compared to MWID over time. Being LTFU among WWID was associated with being HIV-negative and reporting injection risk behaviours and among MWID, younger age, non-participation in OST, being HIV-negative and having protected sex. Despite better NEP compliance among WWID, high injection and sexual risk behaviours in both gender-subgroups, especially in intimate relationships, suggests ongoing HCV and HIV-infection risks. Subgroup-variation in the NEP continuum of care