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ARCHIVED - Report on Sexually Transmitted Infections in Canada: 2008

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Chlamydia (Chlamydia trachomatis)

Chlamydia, an infection caused by Chlamydia trachomatis, has been notifiable nationally since 1990 and remains the most commonly reported bacterial sexually transmitted infection (STI) in Canada. Since asymptomatic infections are common in men and women, affected individuals unaware of their status in the absence of screening could contribute to the spread of infection. Complications associated with untreated infections are also of concern because chlamydia disproportionately affects a younger population, particularly women. A serious, common complication affecting women is pelvic inflammatory disease, which can lead to chronic pelvic pain, ectopic pregnancy, and infertility. Untreated chlamydia in pregnant women can be transmitted to their infants during childbirth, resulting in outcomes such as neonatal conjunctivitis or pneumonia. Less frequently, complications also develop in men, which include epididymoorchitis and other less common conditions1a. As with other non-ulcerative STIs, chlamydia may increase the risk of HIV acquisition and transmission by recruiting HIV susceptible inflammatory cells to the genital tract and by increasing the shedding of HIV-infected cells2a.

Reported rates of chlamydia infections in Canada increased consistently over time.

  • Though chlamydia became reportable in 1990, regular national reporting commenced in 1991. Reported rates decreased steadily until 1997, when this trend reversed (Figure 1).
  • In 2008, 82,919 cases of chlamydia infections were reported, corresponding to a rate of 248.9 per 100,000 (Figure 1). The overall rate in 2008 increased by 80.2% since 1999 (138.2 per 100,000).
  • On average, over the past decade, nationally reported chlamydia rates have increased by 6.8% per year. The change from 2007 to 2008 was sharper than previous years with an increase of 11.1%.
  • Reported rates of chlamydia infections increased consistently over time in both sexes. Between 1999 and 2008, rates in males increased by 107.4% from 81.4 to 168.7 per 100,000, and rates in females increased by 69.1% from 193.6 to 327.4 per 100,000 (Figure 1).
  • Consistent with historical trends, the reported rate in women was almost twice as high as that in men in 2008 (Figure 1).

Figure 1: Reported Rates of Chlamydia by Sex and Overall, 1991 to 2008, Canada

During 2008, reported rates of chlamydia infections continue to be highest in the younger population, particularly females.

  • In 2008, the majority of reported chlamydia infections (82.6%) were among the young population under 30 years of age. This is in contrast to infectious syphilis in which the same age group accounted for only 26.3% of reported cases.
  • In both women and men, the highest reported rates of chlamydia infections were in 20 to 24 year olds, although the rate in women (1,824.3 per 100,000) was more than twice as high as that in men (884.2 per 100,000) (Figure 2).
  • The ratio of female to male rates decreased with age. In the 40 and older age groups, rates were higher in men than in women. (Figure 2).

Figure 2: Reported Rates of Chlamydia by Sex and Age Group, 2008, Canada

Reported rates of chlamydia infections increased across age groups in both males and females aged 15 and older.

  • Over the past decade, among males, the greatest absolute increase in reported rates of chlamydia infections was seen in 20 to 24 year olds. The rate increased from 446.3 per 100,000 in 1999 to 884.2 per 100,000 in 2008 (Figure 3).

Figure 3: Reported Rates of Chlamydia in Males by Age Group, 1999 to 2008, Canada

  • In females, between 1999 and 2008, the greatest absolute increase in reported rates of chlamydia infections was seen in 20 to 24 year olds (Figure 4). The rate increased from 1064.6 to 1824.3 per 100,000.

Figure 4: Reported Rates of Chlamydia in Females by Age Group, 1999 to 2008, Canada

  • Although reported rates in older women remained low compared to other age groups, substantial increases were seen since 1999, especially in 30 to 59 year old women. Between 1999 and 2008, reported rates in 30 to 39 year olds increased by 157.5% (from 94.8 to 244.1 per 100,000) and by 133.9% in 40 to 59 year olds (from 14.8 to 34.7 per 100,000) (Figure 4).

The majority of cases in 2008 occurred in the most populated provinces in Canada, while reported rates of chlamydia infections were highest in the Northern territories.

  • Reported chlamydia rates continue to be highest in Nunavut, the Northwest Territories and Yukon (Table 1).
  • Between 1999 and 2008, the greatest increase in reported chlamydia rates occurred in Manitoba, with an increase of 122.0% (Table 1).
  • In 2008, the national female-to-male chlamydia rate ratio was 2.0:1.0, reflecting that more women than men were reported with chlamydia. Across the country, the ratio ranged from highest in Newfoundland and Labrador (2.9:1.0) to lowest in the Northwest Territories (1.5:1.0).
Table 1: Reported Cases and Rates1 of Chlamydia by Province/Territory, 1999 and 2008, Canada
Jurisdiction Number of Cases Rates per 100,0003 Rate Change (%)
1999 2008 1999 2008 1999–2008
Canada 42,141 82,919 138.2 248.9 80.2
BC 5,402 10,766 134.1 245.7 83.2
AB 5,416 12,047 183.0 336.0 83.6
SK 2,656 5,203 259.0 512.1 97.7
MB 2,967 6,965 259.7 576.6 122.0
ON 13,256 26,245 115.0 203.0 76.5
QC 7,968 15,043 108.4 194.1 79.0
NB 1,136 1,389 150.6 185.9 23.4
NS 1,364 2,033 145.1 216.7 49.3
PE 148 193 107.6 138.0 28.3
NL 433 596 80.1 117.3 46.5
YT 176 232 567.0 700.0 23.4
NT 1,219 870 1,796.4 2,010.0 N/A
NU2 N/A 1,337 N/A 4,251.5 N/A

1 Rate change calculated using unrounded values.

2 Nunavut did not officially become a territory until 1999; prior to 1999, data for Nunavut was combined with Northwest Territories. Rate change for NT was not calculated since 1999 rates are not comparable with 2008 rates due to the creation of Nunavut.

3 Bolded values indicate rates above the national average.

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