[Table of Contents]

Volume: 26S6 - October 2000

1998/1999 Canadian Sexually Transmitted Diseases (STD) Surveillance Report

Genital Chlamydia (Chlamydia trachomatis)

Although the number of reported chlamydia cases in Canada steadily declined from 1992 (when it first became nationally notifiable) to 1997 inclusive, this trend seems to have stopped (Appendix 1.1A and Figure 2) The overall increase in the number of chlamydia cases from 1997 to 1998 was 14%; the proportion among males increased by 27% and among females by 10% over this period. The introduction of NAAT is believed to be a factor in these increases, especially for the males. The overall rate among both sexes increased from 112.7 per 100,000 in 1997 to 128.8 per 100,000 in 1998, making the national goal, of less than 80 cases per 100,000 population by the year 2000⁽²⁾, less attainable.

Age group distribution

The number of cases within each age group as a proportion of the total number of cases changed little from 1992 to 1998, even with the recent increases in chlamydia. Rather, the increase in chlamydial infections in 1998 was spread fairly evenly among all age groups in both sexes, as shown in Figures 3 and 4. However, the 1998 increase among males in each age group was substantially larger than the increase among females in each age group. Among males, the highest rates in 1998 were in the 20-24 year age group (394.1/100,000), representing 37% of all male cases, while among females the rates in the 15-19 age group represented 38% of all female cases (1063.4/100,000). Since chlamydia became nationally notifiable, females have traditionally accounted for approximately 75% of all reported cases, which is attributed at least in part to better screening and case-finding among females rather than reflecting a true female:male distribution.

FIGURE 2 Reported Genital Chlamydia Rates¹ in Canada, 1991 to 1999²

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.
² 1999 numbers are preliminary and changes are anticipated.

Source: Health Canada, Bureau of HIV/AIDS, STD and TB, 2000

FIGURE 3 Reported Male Genital Chlamydia Rates¹ in Canada by Age Group, 1997 to 1999²

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.
² 1999 numbers are preliminary and changes are anticipated.

Source: Health Canada, Bureau of HIV/AIDS, STD and TB, 2000

FIGURE 4 Reported Female Genital Chlamydia Rates¹ in Canada by Age Group, 1997 to 1999²

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.
² 1999 numbers are preliminary and changes are anticipated.

Source: Health Canada, Bureau of HIV/AIDS, STD and TB, 2000

Geographic distribution

Similar to the age group distribution, the regional distribution of the 1998 increase in chlamydia cases is fairly even. Figures 5 and 6 show the provincial/territorial distribution of reported chlamydia rates per 100,000 population from 1997 to 1999 among males and females respectively. Among males, there was an increase in all provinces/territories in 1998, with the exception of Prince Edward Island. Prince Edward Island, having initiated the use of NAAT exclusively for chlamydia in 1996, reported a subsequent increase in the number of cases in 1997, which tapered off in 1998. Proportionately, New Brunswick had the highest increase among females (18% from 1997 to 1998, 625 to 735 cases), and the Yukon Territory had the highest increase among males from 1997 to 1998 (56%, 34 and 53 cases respectively). The latter is particularly interesting as Yukon Territory is the only region that has never introduced NAAT for chlamydia; however, the numbers are too low to draw any conclusions. Almost every province that has introduced NAAT to test for chlamydia has shown a subsequent increase in the number of cases within the following year.

Chlamydia and pelvic inflammatory disease

The many cases of genital chlamydia in females that remain undetected also, for the most part, remain untreated. Untreated chlamydial infections in women can progress to pelvic inflammatory disease (PID) - a painful, sometimes even debilitating, syndrome. It is estimated that 20% to 40% of chlamydia infections progress to PID⁽³⁾. National data on PID incidence are currently limited to hospitalization separation data. Table 1 presents data on known hospitalizations of women of child-bearing age for PID from 1983/84 to 1996/97. It is believed these data represent an underestimation of the true number of cases of PID, most of which are treated on an ambulatory basis.

FIGURE 5 Reported Male Genital Chlamydia Rates¹ in Canada by Province/Territory, 1997 to 1999²

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.
² 1999 numbers are preliminary and changes are anticipated. ^* Nunavut STD data in 1999 are from April 1, 1999

Source: Health Canada, Bureau of HIV/AIDS, STD and TB, 2000

Discussion

Of real concern is the unknown number of asymptomatic cases of chlamydia. Estimates of asymptomatic chlamydial infection range from 40% to 70%, indicating that the true number of chlamydia cases may be much higher than reported. We have seen an increase in cases due partly to the use of newer, non-invasive technology (NAAT); this test is much more acceptable to males than its predecessor, the penile swab. At the same time, NAAT is both more specific and more sensitive than culture. It follows that even more cases will be found if this technology is implemented in widespread screening initiatives. The next step is to broadly promote screening using NAAT among not only high-risk females but asymptomatic high-risk males as well. With widespread testing, we will move towards a clearer picture of the true incidence of genital chlamydia in Canada. Increased screening for both males and females, especially in high-risk groups, is the most efficient way of finding cases in both asymptomatic and high-risk groups.

Table 1 Hospitalizations for Pelvic Inflammatory Disease (PID) in Canada: Cases and Rates^* from 1983/84 to 1996/97

FIGURE 6 Reported Female Genital Chlamydia Rates¹ in Canada by Province/Territory, 1997 to 1999²

¹ Rate per 100,000 population. Population estimates provided by Statistics Canada.
² 1999 numbers are preliminary and changes are anticipated.

^* Nunavut STD data in 1999 are from April 1, 1999

Source: Health Canada, Bureau of HIV/AIDS, STD and TB, 2000

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