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Sexually Transmitted Diseases:
doi: 10.1097/OLQ.0b013e3181b617dc
Articles

Trends in Age Disparities Between Younger and Middle-Age Adults Among Reported Rates of Chlamydia, Gonorrhea, and Infectious Syphilis Infections in Canada: Findings From 1997 to 2007

Fang, Lily MHSc; Oliver, Allison BHSc; Jayaraman, Gayatri C. PhD, MPH; Wong, Tom MD, MPH

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Author Information

Public Health Agency of Canada, Ottawa, Canada.

The authors thank Maureen Perrin and Robert Lerch for their constructive comments on the manuscript, Dena Schanzer for her statistical assistance, and the provinces and territories for their continued efforts in ensuring the success of surveillance of STIs in Canada.

Correspondence: Lily Fang, MHSc, Public Health Agency of Canada, 100 Eglantine Driveway, Ottawa, Ontario, K1A 0K9, Canada. E-mail: Lily_Fang@phac-aspc.gc.ca.

Received for publication March 9, 2009, and accepted June 26, 2009.

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Abstract

Background: The objective was to determine trends in age disparities between reported rates of chlamydia, gonorrhea, and infectious syphilis among younger versus middle-age Canadians.

Methods: We examined age- and sex-specific reported rates of chlamydia, gonorrhea, and infectious syphilis between 1997 and 2007. Sexually transmitted infection (STI) rates in the younger age group (15–29 years) were compared to the middle-age group (40–59 years) over the 11-year period. We used Poisson regression to examine trends in age-specific (younger:middle-age) rate ratios.

Results: Between 1997 and 2007, both the number and rate of reported cases increased for all 3 nationally notifiable STIs. Although chlamydia and gonorrhea rates continued to be higher among younger adults, rates of all 3 STIs increased more dramatically among middle-age adults. Between 1997 and 2007, chlamydia rates increased by 86.8% among adults aged 15 to 29 (P <0.0001) and 165.9% among adults 40- to 59-years-old (P <0.0001). The corresponding increases for gonorrhea were 133.3% (P <0.0001) and 210.2% (P <0.0001) respectively. Infectious syphilis rates increased 5-fold among younger adults compared to an increase of 11-fold among middle-age adults (P <0.0001) since 1997. The reported rate ratios (younger:middle-age) decreased over time for chlamydia (P <0.0001), gonorrhea (P <0.0001), and syphilis (P = 0.005). Males were disproportionately represented among reported chlamydia, gonorrhea, and infectious syphilis cases, constituting 59.8%, 87.6%, and 93.0% of middle-age adult cases, respectively, in 2007.

Conclusions: Middle-age adults may be increasingly affected by chlamydia, gonorrhea and infectious syphilis. There is a need for sexual health information targeting Canada's middle-age adults and their health care providers.

Sexual health is an integral part of wellbeing and sexual activity has been shown to be positively associated with self-reported health and happiness of adults.1,2 Sexual activity does not cease as people grow older although aging brings about natural changes, both physically and mentally, which can affect sexual intimacy and response for many individuals.3,4 Middle-age adults represent a substantial portion of the population in Canada; in 2007, approximately 1 in 3 Canadians were between the ages of 40– and 59–years–old.5 Despite the fact that sexuality is seen as an important part of life for middle-age individuals, the sexual health needs of this population are often overlooked.1 Middle-age adults may not consider themselves to be at risk of contracting a sexually transmitted infection (STI), including HIV, 6–8 and studies suggest that these adults may be less likely to use a condom at their last sexual intercourse with a new partner.9,10

In Canada, the majority of reported STI cases occur among individuals under 25 years of age. However, since 1997, middle-age adults have represented an increasing proportion of nationally reportable STI cases. To this end, the objectives of this article are to determine whether there are age- and sex-specific disparities in the reported rates of chlamydia, gonorrhea, and infectious syphilis among younger versus middle-age Canadians and to determine any trends in the age disparities between 1997 and 2007.

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MATERIALS AND METHODS

Data Source

For the analyses, we used routine surveillance data collected between 1997 and 2007 for all 3 nationally reportable bacterial STIs, chlamydia, gonorrhea, and infectious syphilis. Infectious syphilis includes primary, secondary, and early latent stages. National surveillance data for these 3 STIs is based upon reports of laboratory-confirmed cases in all 10 provinces and 3 territories. Reporting at the provincial/territorial level is mandated under the respective public health legislations. Notification to the federal level is voluntary and jurisdictions provide data through mutual agreements with the Public Health Agency of Canada. Routine data elements that are submitted to the Public Health Agency of Canada include infection, sex, age, and province/territory of residence.

When comparing rate ratios between middle-age and younger adults, cases aged 40 to 59 years were considered middle-age adults and younger adults included those aged 15- to 29–years–old. Much of the published STI data focuses on younger adults, but because of the lack of published data on middle-age adults, we chose to capture this age group in our analyses. As a result, in depth analysis was not performed with the 30- to 39-year age group.

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Data Analysis

To calculate the reported age-specific and sex- and age-specific rates, we used intercensal and postcensal population estimates provided by Statistics Canada.5 We performed trend analysis for the reported age-specific and sex- and age-specific rates of infection using Poisson regression (log linear model) with population as an offset. To account for any lack of fit, a scale parameter was applied. The Cochran-Armitage test was used to test the trend for proportions of reported cases by age group and sex. To compare the disparity of reported rates of STIs between middle-age and younger adults, the annual reported age-specific rate ratio (YMRR) was calculated using the formula R15 to 29/R40 to 59 as previously described by Chesson et al.11 Two-sided P-values <0.05 were considered statistically significant. Analysis was performed using SAS Enterprise Guide 4.1 (Cary, NC).

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RESULTS

Chlamydia

Nationally, the majority of reported chlamydia cases are consistently among 15– to 29–year–olds. However, over time, an increasing proportion of the reported cases were attributable to middle-age adults. Between 1997 and 2007, reported age-specific rates increased by 86.8%, from 466.6 to 871.6 cases per 100,000 (28,778 to 58,771 cases) among young adults aged 15 to 29 (P <0.0001), compared to an increase of 165.9%, from 12.9 per 100,000 to 34.6 per 100,000 (997 to 3387 cases) among adults 40- to 59-years-old (P <0.0001) (Table 1). In comparison, reported age-specific rates increased 164.8% from 71.1 per 100,000 to 188.3 per 100,000 (3662 to 8656 cases) among adults aged 30 to 39 during the same observation period (P <0.0001). Furthermore, the difference in reported rate ratios between younger and middle-age Canadians is decreasing. The YMRR decreased from 36.3:1 in 1997 to 25.5:1 in 2007 (P <0.0001) (Fig. 1) and this decrease was observed in both males (P <0.0001) and females (P = 0.0002) (Figs. 2, 3).

Table 1
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Figure 2
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While younger females continue to be disproportionately affected by chlamydia, with 15- to 29-year-old females accounting for over half of reported infections, in 2007, males accounted for 59.8% of reported cases among adults 40- to 59- years-old compared to 48.5% in 1997 (P <0.0001) (Fig. 4). Among middle-age Canadians, increases in reported cases among both males and females were observed over time, but larger increases were reported among middle-age males compared to their female counterparts (Table 1).

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Gonorrhea

Like chlamydia, although the majority of reported gonorrhea cases continue to be among younger adults, over time, a greater proportion was attributable to middle-age adults. Between 1997 and 2007, reported age-specific rates increased 133.3%, from 49.2 to 114.7 per 100,000 (3033 to 7737 cases) among young adults 15– to 29–years–old (P <0.0001), compared to an increase of 210.2%, from 4.9 to 15.2 per 100,000 (379 to 1502 cases) among adults aged 40 to 59 years (P <0.0001) (Table 1). Among adults aged 30 to 39, reported age-specific rates increased 139.5% from 18.5 to 44.3 per 100,000 (951 to 2036 cases) (P <0.0001). Although the reported rates of gonorrhea increased for both young adults 15 to 29 years and middle-age adults 40 to 59 years, the difference in the YMRR decreased over time, from 10.1:1 in 1997 to 7.6:1 in 2007 (P <0.0001) (Fig. 1). This decrease was observed among both males (P = 0.0002) (Fig. 2) and females (P <0.0001) (Fig. 3) although a more marked decrease was observed among males.

Unlike reported cases of chlamydia, the distribution of reported gonorrhea cases among younger adults was similar between males and females (data not shown).

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Infectious Syphilis

Between 1997 and 2007, reported rates of infectious syphilis increased nearly 8-fold across all age groups (data not shown).12 Although increases were noted for both age groups, age-specific rates in adults 40 to 59 years were 11 times higher in 2007 than in 1997, from 0.4 to 5.3 cases per 100,000 (34 to 527 cases) (P <0.0001), compared to a 5-fold increase among adults 15 to 29 years, from 0.6 to 3.7 per 100,000 (36 to 248 cases) (P <0.0001) (Table 1). A dramatic increase in the reported age-specific rates was also observed for 30 to 39 year olds, with an 8-fold increase from 0.8 to 7.6 per 100,000 (43 to 351 cases) (P <0.0001). Unlike chlamydia and gonorrhea, infectious syphilis is not predominantly reported among younger adults.

Reported rates of infectious syphilis increased among both young adults 15 to 29 years of age and adults aged 40 to 59 years, but the YMRR decreased from 1.3:1 in 1997 to 0.7:1 in 2007 (P = 0.005). The decreases in reported YMRR were not significant for males (P = 0.3) (Fig. 2) or females (P = 0.6) (Fig. 3).

Like chlamydia and gonorrhea, reported age-specific rates and cases of infectious syphilis increased for both males and females between 1997 and 2007 among adults 40- to 59- years-old (Table 1). However, males were disproportionately represented in this age group compared to females, accounting for 93.0% of reported syphilis cases in 2007 compared to 76.5% in 1997 (P <0.0001) (Fig. 4). Reported cases among males aged 15 to 29 years increased over time; during 1997, they represented 33.3% of cases in this age group compared to 71.0% in 2007 (P <0.0001).

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DISCUSSION

From 1997 to 2007, nationally reported rates of all 3 notifiable bacterial STIs have increased steadily across all age groups. Although the majority of reported cases of chlamydia and gonorrhea were among younger males and females, reported rates of chlamydia, gonorrhea, and infectious syphilis have increased more among adults 40 to 59 years in the past decade than among younger adults. Furthermore, larger increases in reported rates were observed among males for chlamydia and infectious syphilis compared to their female counterparts. Additionally, for all 3 STIs, males were disproportionately represented among 40- to 59-year-olds, accounting for 59.8% of reported chlamydia cases, 87.6% of reported gonorrhea cases, and 93.0% of reported infectious syphilis cases in this age group in 2007. The reported rate of infectious syphilis among middle-age males increased 14 times between 1997 and 2007. Outbreaks of syphilis among men who have sex with men (MSM) reported across Canada13,14 and internationally15,16 concentrated among 30- to 49-year-olds could partially explain these increases.

Similar to Canada, the reported age-specific rates of STIs are also increasing among adults in the United Kingdom (UK)17,18 and the United States (US).19,20 To perform international comparisons, rates of STIs in the UK were calculated using population estimates from 1998 and 2007.21,22 In the UK, between 1998 and 2007, the reported rate of chlamydia increased by 178.2% among adults 45- to 64-years-old while in the US the reported rate of chlamydia increased by 181.4% in adults of the same age group between 1997 and 2007. Similarly, the reported rate of gonorrhea in both the UK and the US has increased among adults aged 45 to 64. The UK has seen an increase of 95.9% in the reported rate of gonorrhea from 1998 to 2007 while the rate in the US has increased by 20.3% from 1997 to 2007. The syphilis rate in adults has also increased in the past decade in both countries. Between 1998 and 2007, the UK has seen the syphilis rate increase by 2838.3% in individuals 45 to 64 years of age while in the US, the rate has increased by 45.7% between 1997 and 2007. Similar to Canada, middle-age males in the UK and the US were disproportionately affected and accounted for a greater proportion of both rates and cases than their female counterparts for all 3 reportable STIs (although in the US, the reported rates and cases of chlamydia were similar for males and females).

The number of reported cases of STIs in Canada among those over 60 years of age was small. Any increases in the reported age-specific rates among the 60 years and older age group were driven largely by male cases. In contrast, cases of chlamydia and gonorrhea among people under 15 years are predominantly among females (data not shown due to small sample size). Reported age-specific rates for chlamydia, gonorrhea, and infectious syphilis increased among 30- to 39-year-old males and females between 1997 and 2007, with percent increases similar to those of the 40- to 59-year-old age group.

As the Canadian population ages STI trends may change. More reported cases of STIs may be attributable to middle-age adults since they will constitute a greater proportion of the population. However, the shift in disease trends toward greater numbers of reported cases in middle-age adults does not explain the increasing reported age-specific rates and the observed decreases in reported rate ratios between younger versus middle-age Canadians. Changes in social patterns may in part be contributing to escalating reported rates of STIs. There may be more single, middle-age adults as a result of relationship changes including divorce.11 Also, with the availability of drugs to combat erectile dysfunction or to increase sexual pleasure with other drug use such as “crystal meth,” the sexual behaviors of middle-age adults may have shifted.23

This article is based upon national STI surveillance data and as a result, there are limitations associated with its analysis and interpretation. The number of reported cases is not likely indicative of the true prevalence or incidence of infection and is likely an underestimate of the true burden of infection. Reported cases are laboratory-confirmed and do not include infected individuals who may have been treated based on presenting symptoms and who were not tested. In addition, due to the asymptomatic nature of most STIs, there are likely many infected individuals who are unaware of their infection and who have not come forward for testing. Recommendations in the Canadian Guidelines on Sexually Transmitted Infections advise chlamydia screening for all sexually active youth under the age of 25, pregnant women and older individuals at high risk of infection.24 For gonorrhea and syphilis, the national recommendation is to screen all pregnant women and others at high risk of infection. Another confounding factor in interpreting the trends in reported rates for chlamydia may be the improvements in diagnostic testing methods, which include the introduction of nucleic acid amplification testing (NAAT), which are more sensitive than the previous diagnostic tests.25,26 Furthermore, testing may be becoming increasingly acceptable for men with the introduction of urine-based testing, which can be used with these newer testing methods. In Canada, NAAT is a widely used testing method for chlamydia (for urine, urethral, or cervical specimens). Increasingly, NAAT is also widely used for detecting gonorrhea.

STIs affect people of all ages. Although younger adults in Canada account for higher reported rates of chlamydia and gonorrhea, middle-age adults appear to be increasingly affected, with males aged 40 to 59 being disproportionately affected. Research with middle-age adults has also shown that the topic of sexual health is rarely brought up during visits with their health care provider and they may in turn find it difficult to initiate discussions about sexual health.27 Although individuals have sexual health concerns they wish to discuss with their physician, shame, fear, and embarrassment often prevent them from doing so.27,28 As a result, there is a need for targeted sexual health information for Canada's aging population and targeted continuing medical education for health care providers so that they are able to adequately assess their patients and provide appropriate (age, sex, sexual orientation) sexual health counselling and services.

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