Sexually transmitted infections (STIs) such as chlamydia, gonorrhea and syphilis may not seem like major health issues anymore, but more and more Canadians every year are suffering from these infections. Although reportable STIs besides HIV seemed to be on the decline in the early 1990s, the rates of these STIs are steadily increasing since 1997. The Public Health Agency of Canada (PHAC) reports that chlamydia, the most common

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bacterial STI, has seen a 16.7% increase between 2010 and 2015 (278.5 to 325.0 cases per 100,000), with the greatest rise seen in Quebec and Ontario. In the same time frame, gonorrhea rates rose by 65.4% (33.5 to 55.4 cases per 100,000) and infectious syphilis rates increased by 85.6% (5.0 to 9.3 cases per 100,000). HIV rates in Canada have also seen a marked increase, with an 8.2% rise in 2018 compared to the previous year. It can be hard to explain this trend in a high-income country like Canada, where new prevention and treatment options are becoming increasingly available. In fact, there is both a rise due to new clinical practices and “true rise” in STI rates.

STI screenings were traditionally carried out using bacterial culture-based methods. In the late 90s, Canadian public health units began using nucleic acid amplification testing (NAAT) to screen for STIs, which is now used to diagnose more than 70% of all suspected chlamydia and gonorrhea cases. The use of NAAT has likely contributed to the rise of reported STI cases. For one, NAAT is highly sensitive compared to culture-based tests. It can be performed on urine and using self-collected samples, making it less invasive and more accessible, yet this ease of use comes with a disadvantage. NAAT is less specific than culture-based tests and more likely to produce false positives. The advantages of NAAT mean that more cases of STIs that may have gone undetected using older STI screening tools are now able to be identified, which contributes to the overall increasing trends in STIs. In addition, STI clinics are now testing for oropharyngeal and rectal infections more often, which may also increase the number of cases detected. While new clinical practices play a part in the rise in STI cases over the past two decades, these practices alone do not fully explain the trend.  

Data from the PHAC and the World Health Organization (WHO) shows factors like age, gender and sexual practices make some populations more susceptible to STIs than others. Recent trends in infection rates can identify these key and high-risk populations. When looking at STI cases by age, female cases are younger than males on average. For both males and females, most cases are reported in the younger age groups of 15 to 24 for chlamydia, 20 to 29 for gonorrhea, and 25 to 39 for infectious syphilis. STIs may be more common in younger Canadians due to a number of barriers such as poor knowledge of STIs and risk-reduction behaviours, lack of health care services, confidentiality concerns, embarrassment tied to seeking STI services, and the method of sample collection. Younger women are more biologically susceptible to chlamydia infections, especially when conditions like cervical ectropion co-occur. Women are also more likely to seek health care services and are more often referred to STI prevention and treatment services by physicians than men. Young women are considered a key population for STI surveillance, as chlamydial infections in this demographic are frequently asymptomatic and can lead to serious complications such as pelvic inflammation and infertility.

However, there are also indications that older people are experiencing outbreaks of STIs. Between 2013 and 2017, the largest relative increase in STI rates (62%) was in people aged 60 and older (4.9 to 7.9 cases per 100,000). This can be attributed to a variety of factors such as increases in risky sexual behaviour (loss of fear of pregnancy), psychosocial changes (loss of a spouse), and physiological changes (vaginal drying). These behaviour and biological effects of aging cause older adults to be more susceptible to STIs.

The dramatic increase in gonorrhea and syphilis cases can be partially explained by the increase in cases among men who have sex with men (MSM). It is thought that changes to sexual behaviour among MSM to reduce risk of HIV infection may raise the risk of acquiring other STIs. For example, some MSM choose partners who have the same HIV status (seroconcordant) to allow for unprotected sex and to reduce the risk of transmitting or acquiring HIV. However, other STIs can often spread freely between men who do so. Similarly, serosorting with one or more partners taking pre-exposure prophylaxis (PrEP) as a preventative measure for HIV infection may also provide a false sense of security and reduce condom usage, increasing the risk of contracting other STIs. Another concern is the use of social media and mobile apps that are used to find sexual partners. These may promote multiple casual partnerships, more frequent new partners, and more rapid partner turnover, all of which are risk factors for STI acquisition.

Another issue that plays a significant role in the spread of bacterial STIs is antibiotic resistance. More than half of Neisseria gonorrhoeae strains isolated in 2017 were resistant to at least one antibiotic used to treat gonorrhea infections. This resistance can lead to ineffective treatment and further transmission of resistant strains. Failure to adhere to treatment guidelines also contributes to the spread of these strains.

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It is unclear how the coronavirus pandemic will impact STI trends in Canada. It is likely that STI screening will decrease as hospital resources are diverted and Canadians stay home. Many questions are left unanswered as to whether the true incidence of STIs will increase or decrease in response to the pandemic.

STIs are not a uniquely Canadian problem, as many other high-income nations such as the United States, the United Kingdom, and Australia report similar infection statistics. STIs are no longer the deadly plagues they once were, but they are still a major public health concern and further measures must be taken to control the spread of these diseases. New diagnostic tools such as NAAT have proven crucial in understanding the full scope of the epidemic. Further research and surveillance of this silent epidemic is needed to understand the many reasons why STI rates are increasing in key populations. With more data, public health centers will know how to best direct prevention and treatment resources in order to slow the spread of STIs.


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Choudhri, Y., Miller, J., Sandhu, J., Leon, A. & Aho, J. Chlamydia in Canada, 2010–2015. Canada Communicable Disease Report 44, 49–54 (2018).

Choudhri, Y., Miller, J., Sandhu, J., Leon, A. & Aho, J. Gonorrhea in Canada, 2010–2015. Canada Communicable Disease Report 44, 37–42 (2018).

Choudhri, Y., Miller, J., Sandhu, J., Leon, A. & Aho, J. Infectious and congenital syphilis in Canada, 2010–2015. Canada Communicable Disease Report 44, 43–48 (2018).

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Patrick, D., Wong, D., & Jordan, R., Sexually Transmitted Infections In Canada: Recent Resurgence Threatens National Goals. Canadian Journal of Human Sexuality. 9, 149-168 (2000).

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Rekart, M. L. & Brunham, R. C. Epidemiology of chlamydial infection: are we losing ground? Sexually Transmitted Infections 84, 87–91 (2008).

WHO. Report on global sexually transmitted infection surveillance. (2018).

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