Can J Public Health. 2026 Jul 2. doi: 10.17269/s41997-026-01226-6. Online ahead of print.
ABSTRACT
OBJECTIVES: This study examined temporal trends in co-infection associated with sexually transmitted and blood-borne infections (STBBIs) in Ontario and assessed associations with behavioural, social, and structural determinants within a syndemic framework.
METHODS: A retrospective, population-based approach was used to analyse 269,814 positive test records for chlamydia, gonorrhea, syphilis, and HIV from Ontario’s public health notifiable diseases database across seven Public Health Units (PHUs) between 2013 and 2023. Co-infection was defined as ≥ 2 STBBIs diagnosed within 14 days. Descriptive statistics, Chi-square, and multivariable logistic regression were used to identify behavioural, social, and structural predictors of co-infection. Area-level marginalization was assessed using ON-Marg indices.
RESULTS: STBBI rates steadily increased across all PHUs over the study period, with Toronto, Northwestern, and Thunder Bay District showing the highest burden. Co-infections accounted for 5.71% of infection episodes and increased significantly over time, with a 10.20% annual increase estimated using negative binomial regression (p = 0.010). Male and transgender individuals had higher odds ratios of co-infection compared to females. Behavioural factors (anonymous sex, multiple partners, condomless sex, substance use) and social vulnerabilities (underhoused/homeless, survival sex, sex work) were associated with co-infection. ON-Marg dimensions in housing, material resources, and racialized populations were also associated with higher co-infection rates while age/labour force marginalization showed an inverse relationship.
CONCLUSION: The findings provide evidence consistent with syndemic patterns among STBBIs in Ontario, shaped by behavioural, social, and structural inequities. Integrated, equity-focused interventions and improved integration of co-infection data within disease surveillance systems may support more effective prevention strategies as co-infection rates rise.
PMID:42390728 | DOI:10.17269/s41997-026-01226-6
