Increasing rates of Chlamydia trachomatis infection in Alberta, Saskatchewan, and Manitoba compared to Canada overall, between 1991 and 2022

• Chlamydia incidence has increased in different Canadian provinces, particularly Alberta, Saskatchewan and Manitoba. • Alberta, Saskatchewan and Manitoba incidence rates have been 1.5–2 times the national average. • Females and people aged 15–29 are the most severely affected groups. • Rising chlamydia incidence in adults aged 30–39 underscores gaps in current screening priorities. • While females are tested more often, males show higher positivity, suggesting a substantial number of hidden cases. • Limited reporting on LGV, equity indicators and coinfections hinders targeted interventions. Chlamydia trachomatis is the most commonly encountered sexually transmitted infection. Our objective was to describe the evolution of chlamydia incidence rates in Alberta, Saskatchewan, and Manitoba as compared to Canada overall, from 1991 to 2022. We conducted an ecological study, collecting data on chlamydia infection from publicly available reports throughout Canada, laying special emphasis on Alberta, Saskatchewan, and Manitoba. As variables, we used: Chlamydia incidence rate per 100,000 inhabitants, stratified by sex, age group, ethnicity, province, and year. In 1991, chlamydia incidence in Alberta (265.0/100,000), Saskatchewan (328.2/100,000), and Manitoba (410.2/100,000) largely exceeded the nationwide rate (164.0/100,000). Incidence subsequently increased dramatically, peaking between 2013 and 2019 (Canada overall: 335.1/100,000; Alberta: 399.9/100,000; Saskatchewan: 534.6/100,000; Manitoba: 604.5/100,000). Females aged 20–29 years accounted for 61.6% of the cases, while incidence in individuals aged 30–39 pronouncedly increased. Coinfection rates with Neisseria gonorrhoeae increased in Alberta (1998–2006) from 2.1% to 5.2% and decreased in Manitoba (2004–2012) from 14.8% to 9.8%. One case of lymphogranuloma venereum was reported in Canada in 2004, 36 in 2005, and 96 between 2004 and 2011. Data on other equity indicators are limited or nonexistent. Between 1991 and 2022, the incidence of chlamydia infection increased across Canada and, more particularly, in three provinces (Alberta, Saskatchewan, and Manitoba), which consistently reported chlamydia infection incidence rates 1.5 to 2 times the national average. Young people and females were the most severely affected groups. More complete and consistent epidemiological data, which would include incidence disaggregated by equity indicators, are crucial to addressing the increasing burden of chlamydia in Canada and, more particularly, the Prairie provinces