People who are incarcerated (PWAI) and correctional staff face a higher risk of communicable diseases. This study assessed the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and sexually transmitted bloodborne infections (STBBIs) in British Columbia (BC) Provincial Correctional Centres (PCCs). A multicentre cross-sectional serosurvey was conducted from January 4 to February 14, 2021, among PWAI and staff. Antibody and molecular screening assessed pathogen prevalence, with Pearson’s chi-squared tests for group comparisons. Mixed-effects logistic regression explored clinical and sociodemographic factors associated with SARS-CoV-2 or STBBIs. Among PWAI (n=299), seroprevalence was 5.5% for SARS-CoV-2, 14.6% for hepatitis C virus, and 1.3% for syphilis. Among staff (n=505), seroprevalence was 2.9% for SARS-CoV-2, 1.7% for hepatitis B virus, and 0.6% for syphilis. Among PWAI, lower education (adjusted odds ratio [aOR]=2.38, 95% confidence interval [CI]: 1.02-5.56), unstable employment (aOR=2.86, 95% CI: 1.16-6.67), and opioid use (aOR=3.56, 95% CI: 1.15-12.65) were associated with STBBI acquisition. Among staff, working in a PCC with a SARS-CoV-2 outbreak was associated with infection acquisition (aOR=7.97, 95% CI: 2.28-27.97). The ongoing presence of SARS-CoV-2 and STBBIs in correctional facilities highlights the need for balanced public health interventions addressing both transmissions, ensuring timely prevention, testing, and treatment for all individuals.