Section 3: Report on Sexually Transmitted Infections in Canada: 2012 – Infectious Syphilis (Treponema pallidum)

3. Infectious Syphilis (Treponema pallidum)

Syphilis, an infection caused by the bacterium Treponema pallidum, has been nationally notifiable since 1924. If left untreated, it progresses through primary, secondary, latent, and tertiary stages. While all stages of syphilis are nationally notifiable, only primary, secondary, and early latent syphilis (less than 1 year after the point of infection) are considered infectious and therefore are of major public health significance. As a result, only these stages are included in national reports.

After several years (or even decades), untreated syphilis can progress to tertiary syphilis, in which serious complications occur, causing damage to the central nervous system, cardiovascular system, eyes, skin, and other internal organs. It may even be fatal^{Footnote 46}. Individuals infected with syphilis are also at an increased risk of contracting HIV, and those co-infected with both pathogens are more likely to transmit HIV to their sexual partners^{Footnote 3}. In co-infected individuals, there is a greater chance of rapid progression to serious consequential conditions, such as neurosyphilis, often while those individuals are still infectious^{Footnote 47}-^{Footnote 49}.

3.1 National Trends

Trends over Time

From 1993 to 2001, rates of reported cases of infectious syphilis were very similar between males and females, with both sexes experiencing low rates over this time frame. In 2001, rates began to climb sharply, particularly among males; this trend continued through to 2012 (Figure 10). In 2012, 2003 cases of infectious syphilis were reported, corresponding to a rate of 5.8 per 100,000 and a 101.0% increase from the 2003 rate of 2.9 per 100,000. The majority of cases (94.9%) reported in 2012 were among men. Between 2003 and 2012, rates among males increased by 128.3% from 4.8 to 11.0 per 100,000; conversely, rates among females decreased by 40.9% from 0.9 to 0.5 per 100,000.

Trends by Age Group and Sex

As in previous years, in 2012, the majority (65.6%) of all reported cases of infectious syphilis were among men aged 30 years and older. The highest rates were among men aged 25 to 29 years, followed by men aged 20 to 24 years (21.5 and 21.2 per 100,000, respectively) (Figure 11). Among women, rates of reported cases of infectious syphilis were substantially lower; the highest rates among women were observed among those aged 20 to 24 years, followed by those aged 15 to 19 years (2.2 and 1.3 per 100,000, respectively).

Between 2003 and 2012, relative rate increases were observed in males of all age groups, with the exception of those the 10 to 14 age group where zero cases were reported in 2003 and 2012. The greatest relative rate increase occurred in males aged 15 to 19 years (731.2%, from 0.7 to 6.1 per 100,000), followed by males in the 20 to 24 age group (634.6%, from 2.9 to 21.2 per 100,000) (Figure 12). From 2003 to 2012, rates decreased among females of all ages, with the exception of those aged 0 to 14 where zero cases were reported and those in the 15 to 19 age group where rates increased by 12.1% from 1.2 to 1.3 per 100,000 (Figure 13). The greatest rate decrease among females was observed in those aged 25 to 29 years, whom experienced a relative decrease of 71.9%, from 3.3 to 0.9 per 100,000. Of note is that due to low number of infectious syphilis cases reported among females, rates are quite variable and thus relative rate changes should be interpreted with caution.

Trends by Province/Territory

In 2012, the rate of reported cases of infectious syphilis was highest in Quebec (8.4 per 100,000), followed by Nova Scotia (6.7 per 100,000) (Table 4).

The number of cases of infectious syphilis in Canada is low relative to other STIs and, as a result, population rates tend to be variable and unstable, thereby rendering it difficult to interpret changes over time. Between 2003 and 2012, rates of reported cases of infectious syphilis increased in all jurisdictions, with the exception of Yukon, British Columbia, Manitoba and Saskatchewan. Over this ten year period, outbreaks of infectious syphilis were reported across most jurisdictions in Canada.

3.2 Congenital Syphilis

Congenital syphilis is caused by the transmission of T. pallidum from an infected pregnant woman to her fetus. The majority of infants with congenital syphilis are infected in utero, but they can also be infected by contact with an active genital lesion at the time of delivery. The risk of transmission in untreated women varies with the stage of disease; the risk is 70-100% with primary or secondary syphilis, 40% with early latent syphilis and 10% in late latent stages in pregnancy^{Footnote 46}. Routine prenatal screening for syphilis and prompt treatment of infection is an important way to prevent congenital syphilis and associated sequelae. Lack of appropriate prenatal care is the primary factor in the failure to prevent congenital syphilis infection^{Footnote 50Footnote 51}.

Syphilis can result in serious complications in pregnancy, such as spontaneous abortion, stillbirth, or perinatal death. Live-born infected children can suffer serious consequences, usually within the first 3 months of life. Consequences include cerebral palsy, hydrocephalus, sensorineural hearing loss, and musculoskeletal deformity, all of which may be prevented with timely treatment during pregnancy^{Footnote 52}. However, some manifestations develop much later. Only early congenital syphilis cases (diagnosed in infants less than 2 years of age) are currently reported nationally.

Rates of reported cases of congenital syphilis were less than 1 per 100,000 live births before 2005, after which a significant increase in rates was observed; an apex of 2.6 per 100,000 live births was observed in 2009. Data suggest that the increase in reported congenital syphilis cases observed over this time frame was linked to outbreaks of infectious syphilis among heterosexuals in corresponding regions across Canada^{Footnote 53}. Since 2009, occurrences of congenital syphilis have declined, reaching a rate of 0.8 per 100,000 live births in 2011; in 2012, three cases of congenital syphilis were reported nationally, however, due to the unavailability of live birth data at the time of publication, a rate could not be calculated (Table 5).

3.3 Summary

After years of near-zero incidence of infectious syphilis, in 2001, rates of reported cases of infectious syphilis began to increase dramatically and continue to do so. This resurgence may be due largely to transmission among some MSM who engage in high-risk sexual practices. These include the use of "club drugs" and other substances that decrease inhibitions and impair decision making during sexual activity, as well as the practice of seeking sex partners on the Internet and in venues such as bathhouses, which are associated with higher-risk sexual activity^{Footnote 39 Footnote 54 Footnote 56}. Increasing STI rates among MSM have also been observed in the United States and Europe; the causes for these increases are complex and include demographic shifts, as well as changing sexual attitudes and social contexts related to increased risky sexual behaviour^{Footnote 54}.

In HIV-positive MSM, co-infection with syphilis is common and of considerable concern. In some studies, increased rates of syphilis and other STIs among MSM have been associated with the practice of serosorting, i.e. the choosing of sexual partners whose HIV status is the same as one's own^{Footnote 57}-^{Footnote 59}. Serosorting in HIV-positive MSM may contribute to the rapid increases in infectious syphilis rates observed among males in Canada. HIV accelerates the progression of syphilis infection and increases the likelihood of neurological manifestations, particularly in the early stages of infection. Increases in early neurosyphilis have been noted in HIV-positive MSM^{Footnote 60Footnote 61}.

Heterosexual outbreaks of syphilis have been observed mainly among sex workers and their clients, and street-involved people ^{Footnote 56Footnote 62Footnote 63}. Syphilis in women of childbearing age is of particular concern because of the potential for vertical transmission leading to congenital syphilis in infants exposed in utero to T. pallidum. Prenatal screening for syphilis in all pregnant women is a standard of care across Canada^{Footnote 46}. Currently, congenital syphilis rates appear to be reaching pre-2005 levels, an encouraging trend that will continue to be monitored over time.

Making comparisons in infectious syphilis rates internationally is complicated by differences in surveillance practices. In the United States, only cases of primary and secondary infection are included in annual rates. In Australia, England and Canada, early latent cases are also included in reporting. Furthermore, there are notable differences in the definition of early latent syphilis among these four countries. In England and Australia, early latent syphilis is defined as an asymptomatic individual with syphilis who has acquired the infection in the past 2 years; in Canada and the United States, the individual must have acquired the infection in the last 1 year to be considered early latent.

Overall rates of infectious syphilis were lowest in the United States (5.0 per 100,000)^{Footnote 22},^{Footnote 23}, although this estimate does not include early latent cases. For countries that included early latent syphilis cases, Australia had the highest rate (6.7 per 100,000)^{Footnote 24}, while in England the rate was 5.6 per 100,000^{Footnote 25} compared to Canada's rate of 5.8 per 100,000. Due to differences in reporting practices, differences in annual rates of infectious syphilis across countries should be interpreted with caution.

Figure 10: Overall and sex-specific rates of reported infectious syphilis, 1993 to 2012, Canada

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Figure 11: Rates of reported infectious syphilis by sex and age group, 2012, Canada

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Figure 12: Rates of reported infectious syphilis in males by age group, 2003 to 2012, Canada

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Figure 13: Rates of reported infectious syphilis in females by age group, 2003 to 2012, Canada

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