Chlamydia (Chlamydia trachomatis)

[Table of Contents]

Volume: 25S1 - May 1999

Sexually Transmitted Diseases in Canada: 1996 Surveillance Report
(with Preliminary 1997 Data)

While genital chlamydia is still the most commonly reported bacterial STD in Canada, there has been a steady decline in the number of reported cases since it became nationally notifiable in 1990, from 48,284 cases (171.7 per 100,000) in 1991 to 34,399 cases (114.8 per 100,000) in 1996 (Figure 2). However, the incidence of chlamydia infection still remains high, especially among young women (998.6 per 100,000 and 941.2 per 100,000 for 15-19 year old and 20-24 year old women respectively in 1996) (Figure 3). The male to female case ratio since 1991 has remained remarkably stable at approximately 1:3. Additionally, estimates of asymptomatic cases of chlamydia in women have been as high as 85%^(2-4), thus the actual incidence of the disease may be much greater than reported. The higher rate of infection among females is deemed to be a reflection of a combination of screening of asymptomatic females and low rates of testing in men. Males have been deterred from testing because of the discomfort associated with obtaining the urethral specimen for culture. Recently introduced non-invasive (urine) tests may increase the number of tests done in both females and males, especially the latter. This, in turn, may increase the reported incidence of chlamydia among both sexes.

FIGURE 2 Reported Genital Chlamydia Rates¹ in Canada, All Ages, 1991-1997²

FIGURE 2 Reported Genital Chlamydia Rates1 in Canada, All Ages, 1991-1997

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada. ² 1997 num bers are preliminary and are expected to change.

FIGURE 3 Reported Genital Chlamydia Rates¹ in Canada by Age Group and Sex, 1996

FIGURE 3 Reported Genital Chlamydia Rates1 in Canada by Age Group and Sex, 1996

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.

The sequelae of untreated (which includes undetected or asymptomatic) chlamydial infections can be severe: it has been estimated that in 20-25% of infected, untreated women the condition will progress to pelvic inflammatory disease (PID)⁽⁵⁾, and subsequently these women will be exposed to the complications of ectopic pregnancies (see Sequelae of STD: Pelvic Inflammatory Disease and Ectopic Pregnancy) and/or tubal infertility.

The regional distribution of chlamydia in Canada has remained relatively constant since the disease became nationally notifiable. The north - the Yukon Territory and the Northwest Territories - has traditionally had the highest incidence of chlamydia with a range of 3 to 14 times the national rate respectively, and Newfoundland has had the lowest (48.8 per 100,000 in 1996) incidence rate (Figure 4, Appendices 1.1 - 1.2).

Of great concern is the incidence rate of STD among children as an indicator of sexual abuse. Figure 5shows the incidence rate of chlamydia among children <10 years old from 1991 to 1997, by sex of child.

The national goal for chlamydia is 80 cases per 100,000 for the year 2000. The 1996 incidence rate of 114.8 per 100,000 indicates that this goal has been partially achieved to date. For women in the 15 to 24 year age group, the goal is 500 per 100,000 (1996 rate is 968.9 per 100,000 among women in this age group)⁽⁶⁾. These goals are ambitious but emphasize the need to further reduce STD levels in Canada.

FIGURE 4 Reported Genital Chlamydia Rates¹ in Canada by Province/Territory and Sex, 1996

FIGURE 4 Reported Genital Chlamydia Rates1 in Canada by Province/Territory and Sex, 1996

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.

FIGURE 5 Reported Genital Chlamydia Rates¹ Among Children <10 years, Canada, 1991-1997²

FIGURE 5 Reported Genital Chlamydia Rates1 Among Children <10 years, Canada, 1991-1997

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada. ² 1997 numbers are preliminary and are expected to change.

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	Last Updated: 2002-11-08		Important Notices