The evolving HIV epidemic in Ontario, Canada: A retrospective analysis of new HIV diagnoses to identify subpopulations with persistent risk of HIV transmission.

Objective: The objective of this study was to characterize new HIV diagnoses in key Ontario cities, in order to understand current drivers of continued HIV transmission to inform HIV testing and prevention efforts.

Methods: Chart reviews were carried out at four clinical sites in Ontario, Canada. The study population included individuals who were diagnosed with HIV in Ottawa, Hamilton, and Toronto between January 1, 2018, and December 31, 2020, and had no previous evidence of HIV documented.

Results: The total number of persons in this analysis was 359, from Toronto (n = 201), Ottawa (n = 88), and Hamilton (n = 70). More than half of the diagnoses were among those who immigrated to Canada, and many were diagnosed (11%) during the year they arrived. Many participants experienced a late diagnosis (43.2%), and while 116 (32.3%) had HIV testing history in Ontario, 155 did not (43.2%). Many participants were men who have sex with men (MSM) and had a previously recorded diagnosis of gonorrhea or chlamydia (n = 27; 7.5%) or syphilis (n = 39; 10.9%). Among women and heterosexual men, a diagnosis of hepatitis C (n = 18; 5.0%) appeared to signal a risk of HIV diagnosis.

Conclusion: These data show that HIV testing and prevention strategies should be targeted to (1) MSM with a history of syphilis, gonorrhea, or chlamydia; (2) heterosexual men and women with a history of hepatitis C; and (3) immigrants within the first 5 years of migration. To address the evolving epidemic, it will be necessary to employ targeted HIV screening and prevention measures.