A Health Surveillance Update on Canadian Children and Youth

Chlamydia

Since 1991, chlamydia has been the most commonly reported bacterial sexually transmitted disease in Canada.

Chlamydia trachomatis is a bacterial pathogen that is increasingly recognized as an important cause of sexually transmitted diseases (STDs).⁽³⁾ Since 1991, chlamydia has been the most commonly reported bacterial sexually transmitted disease in Canada.⁽⁴⁾ In adolescent males and females, genital chlamydial infections are frequently asymptomatic.⁽⁵⁾ Yet, the sequelae of chlamydia cervicitis are substantial and include pelvic inflammatory disease (PID) and subsequent ectopic pregnancy or infertility.⁽⁵⁾ Genital Chlamydia trachomatis infections became nationally notifiable in 1990. The chlamydia rate presented is the number of reported genital chlamydia infections per 100,000 persons per year.

In 1996 in Canada, there were 34,399 cases of chlamydia reported from all age groups for a rate of 114.8 per 100,000.⁽⁴⁾ There were 9,752 cases reported in females in the 15-19 year age group for a reported chlamydia rate of 998.6 per 100,000, almost nine times higher than the overall reported chlamydia rate. There were 1,524 cases in adolescent males aged 15-19 years, for a rate of 148.5 per 100,000. The male to female case ratio has remained stable since 1991 at approximately 1:3 in the general population. However, in the 15-19 year age group, there is a much greater sex difference, reflected in a male to female case ratio of 1:6 since 1991. The greater number of cases among females may be due to screening of asymptomatic women and low rates of testing among males. Recently developed non-invasive urine testing for chlamydia infection may increase the number of diagnostic tests performed, particularly among males. This may increase the number of reported cases of chlamydia in the near future. As depicted in Figure 3, the reported chlamydia rate in 15-19 year olds has been decreasing since 1991.

Source: Bureau of HIV/AIDS, STD and TB, LCDC⁽⁴⁾

International comparisons of the chlamydia rate among 15-19 year olds are limited. As depicted in Figure 4, Canada has a considerably lower reported chlamydia rate among 15-19 year olds than the United States.⁽⁶⁾ Differences in chlamydia rates between Canada and the United States may be due to differences in reporting systems, access to health care and/or screening practices between the two countries.

Source: Bureau of HIV/AIDS, STD and TB, LCDC^(4,6)

Data limitations
The chlamydia rates presented likely underestimate the true chlamydia incidence among Canadian adolescents because of the high proportion who are asymptomatic and therefore do not seek medical attention. In addition, the reporting requirement of laboratory confirmation likely reduces the number of notifications. Furthermore, the introduction of new diagnostic tests or changes in screening practices may limit the interpretation of trends over time in reported chlamydia rates.

Summary
Despite a decreasing incidence of reported chlamydia in Canada, chlamydia remains the most commonly reported bacterial sexually transmitted disease, and youth is the group most affected by this STD. Control of chlamydia, as well as other STDs, is likely to improve if appropriate attention and resources are given to specific programs on screening, patient management, education, partner notification and social/sexual networking analysis. Ongoing surveillance is required to monitor the progress in attaining the national goals of reducing the burden of sexually transmitted diseases in Canada.

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