The Canadian Journal of Human SexualityVolume 6 - Number 2 1997 The Control of Sexually Transmitted Diseases in Canada: A Cautiously Optimistic OverviewDavid M. Patrick Abstract:Canada has made substantial progress in the control of some sexually transmitted diseases. Rates of gonorrhea and syphilis have declined significantly. Rates of chlamydia are also declining, but to a lesser extent. Although there are less precise data on the incidence of viral STDs (HIV, HPV, genital herpes), it is likely that rates of these STDs have not fallen significantly. Successful interventions aimed at curable STDs have included screening, curative therapy, and partner notification/treatment. The absence of cures for viral STDs indicates a need for enhanced behavioural interventions and greater focus on subgroups of the population with high levels of infection. With proper planning and implementation, STD control and prevention programs can dramatically reduce STD morbidity in Canada. Keywords:
Acknowledgements:The author wishes to acknowledge Ms. Dorothy Rachar and Ms. April Accola for assistance in manuscript preparation, and the staff of the Division of STD Prevention and Control, Laboratory Centre for Disease Control, Bureau of HIV/AIDS and STD, for provision of data and organizing the meeting on national goals for STD, Health Canada. Correspondence concerning this paper should be addressed to David M. Patrick, Associate Director, Division of STD/AIDS Control, British Columbia Centre for Disease Control, 828 West 10 Avenue, Vancouver, BC V5Z 1L8. Tel: 604-660-6161; Fax: 604-775-0808; email: dmpatric@bcsc02.gov.bc.ca IntroductionSexually transmitted diseases (STDs) are caused by a daunting menagerie of microbial pathogens including bacteria, viruses, protozoa and ectoparasites (Table 1). Despite the stigma attached to the sexual transmission of such agents, the importance of sexual transmission may be a strategic common pathway for dealing with related issues in reproductive health, including cancer of the cervix, family planning and unwanted pregnancy (Wasserheit, 1996). Papers presented at a recent meeting to establish national goals for sexually transmitted diseases and sexual risk behaviour *** demonstrated that Canada has made significant progress in reducing the incidence of some STDs. This issue of the Canadian Journal of Human Sexuality (CJHS) features expanded versions of a number of these papers (Alary, 1997; Patrick, 1997; Maticka-Tyndale, 1997; Romanowski, 1997; Lytwyn & Sellors, 1997; MacDonald & Brunham, 1997; Steben & Sacks, 1997), plus others on related topics (Fisher, 1997; Tepper & Gully, 1997). In a subsequent issue of CJHS, Rekart (1997, in press) offers a critical analysis of the key policy and practice issues facing the frontline STD control programs that are mandated to implement many of the recommendations in these papers. This paper offers a review of the achievements, opportunities and shortcomings of our national approach to prevention of STDs. Some of the general and specific goals for STD control identified by the authors of this issue of CJHS are discussed, and it is suggested that health professionals, educators, policy makers, and governments in Canada have an unprecedented window of opportunity to make a major impact on the burden of STDs and their sequelae in Canada. *** Meeting of the Expert Working Group to Establish Goals for STD and Sexual Risk Behaviour, November, 1996. Sponsored by the Division of STD Prevention and Control, Bureau of HIV/AIDS and STD, Health Canada Overview of the Epidemiology of Bacterial STDsChlamydia TrachomatisChlamydia is the most frequently reported of all communicable diseases in North America (CDC, 1996; CDC, 1993; Gully, 1992). In Canada, the reported rate fell from 162 per 100,000 in 1992 to 123 per 100,000 in 1995 (Bureau of HIV/AIDS and STD, 1996). A number of studies indicate that incidence may be declining in settings where control measures are in place (Crowley, Horner, & Nelki, 1994; Hillis et al., 1994; Garland, Gertig, & McInnes, 1993; Patrick & Bowie, 1994). However, even in populations where there has been an overall decline in reporting, rates remain unacceptably high among sexually active young women under the age of 25 years. Reported infections exceed 1% annually for these women who, as a group, are most affected by the complications arising from infection (Gully, 1992). Because many new infections go undetected and untreated, prevalence rates as high as 5-10% are common in women 15-24 (CDC, 1993; Garland, 1993). Among other vulnerable populations, such as male and female street youth, cumulative incidence as measured by serological survey is as high as 22% (Ram et al., 1996). An appropriately focused public health approach to genial chlamydia could reduce the overall rate to 80 per 100,000 by the year 2000 (about a 30% reduction), and the rate in women aged 15-24 to 500 per 100,000 (about one half the 1995 rate) (Patrick, 1997). This kind of reduction, if sustained, would have a major impact in reducing the future reproductive health problems and costs associated with asymptomatic (and hence untreated) infection. GonorrheaBetween 1980 and 1995, the reported rate of Neisseria gonorrhea plummeted over ten-fold from 216.6 per 100,000 population to 18.6 per 100,000 (Alary, 1997). Not surprisingly, rates in 1995 for 15-24 year olds of both sexes were three to four times higher than the overall average. Rates also varied considerably between provinces in 1995. For example, Quebec and Eastern Canada were below the national average of 18.6 per 100,000; whereas, Manitoba was 3 times, and the Northwest Territories 9 times, the national average (Alary, 1997). In contrast to Chlamydia trachomatis, Neisseria gonorrhoeae has demonstrated a remarkable ability to acquire antimicrobial resistance by a variety of genetic mechanisms. Plasmid-mediated penicillin resistance emerged rapidly in the 1980s and peaked at 1,136 isolates across Canada during 1990. By 1994, a decline in the number of penicillinase-producing strains was noted. This may be because selective pressure was removed by the replacement of ampicillin with other drugs in many parts of the country. However, in 1994, as many as 21.3% of isolates (1,313 in all) still carried some form of plasmid-mediated resistance (mostly high-level tetracycline resistance) and 318 strains had chromosomally mediated resistance patterns. Further progress against gonorrhea will require due attention to antimicrobial susceptibility, partner networks and core groups in whom the infection is still endemic. Given current trends in Canada, and the evidence for successful reduction of gonorrhea rates in Northern Europe, Alary (1997) views the elimination of locally transmitted N. gonorrhoeae in Canada by the year 2010 to be an attainable goal. Pelvic Inflammatory Disease (PID) and Tubal InfertilityBoth gonorrhea and chlamydia are a source of considerable costs to the health care system, most of which are associated with pelvic inflammatory disease (PID) and its complications (Institute of Medicine, 1996). One in ten American women report at least one episode of PID during their reproductive years (Aral, Mosher, & Cates, 1991) and 6.5% of women attending a contraception service in Calgary reported a history of PID (MacDonald & Brunham, 1997). However, many women with tubal infertility, scarring, and/or positive chlamydia serology give no history of symptoms or PID diagnosis. The Laboratory Centre for Disease Controls (LCDC) tracking of Statistics Canada hospital morbidity for PID in ten provinces from fiscal 1983/84 to 1993/94, showed that the rates in 15-44 year old women declined from 281.8 to 125.5 per 100,000 women over that period (MacDonald & Brunham, 1997). Findings from such studies are limited by the fact that 80-85% of PID is managed outside of hospitals; indeed economic pressure may continue to reduce the likelihood of hospitalization for PID. Fortunately, a Manitoba study has confirmed that outpatient visits for PID were also down 33% and hospital visits down 48% between 1981-1990 (Orr et al., 1994). Because Chlamydia trachomatis and Neisseria gonorrhoeae account for a large proportion of preventable PID, and because there are numerous shortcomings in the clinical diagnosis of that syndrome, MacDonald and Brunham (1997) link their national goal of a 50% reduction in PID by the year 2007 to the parallel goals of eradication of endemic gonorrhea by 2002 and a 50% reduction in chlamydia by 2007. Since PID is a syndrome frequently caused by organisms other than STD pathogens, it can be markedly reduced, but not eliminated, by control of STDs. Infectious SyphilisThe decline of infectious syphilis in Canada has paralleled that of gonorrhea with a ten-fold decrease between 1984 and 1994 to a national rate in 1995 of 0.5 per 100,000 (Romanowski, 1997). With so few new infections, imported cases have become an importat means by which existing rates are sustained. Control efforts have necessarily become more outbreak-focused, and rely on effective partner notification and treatment more than ever. Romanowski (1997) recommends continued vigilance, however, to maintain the current overall low rate and to identify and treat pockets of infection. Overview of the Epidemiology of Viral STDsHIV/AIDSAlthough Acquired Immune Deficiency Syndrome (AIDS) has been reportable in Canada since the early 1980s, we are only now obtaining information on the extent of HIV infection on a national level. It is estimated that 33,520 positive tests for HIV had been recorded to December 31, 1994 across Canada, and that 3,093 people tested positive for the first time during 1995 (personal communication, Bureau of HIV/AIDS and STD, Laboratory Centre for Disease Control, Health Canada, 1997). In some provinces, the number of people testing positive for HIV for the first time exceeds the number of reports of gonorrhea and syphilis combined (Rekart, 1996). While there is some reason to hope that the spread of HIV by the sexual route has levelled off, behavioural changes required to sustain this pattern are hard to maintain. An explosion of HIV infection among injection drug users is now shaping the course of the future epidemic. When it comes to viral STDs other than HIV, our knowledge of epidemiology is unsatisfactory. Human papilloma viruses (HPV) and herpes simplex virus (HSV) are not uniformly reportable across Canada. Even if they were, interpretation of report data would be difficult, as infections persist for long periods or for life, may be diagnosed at any point in the natural history, are often not clinically evident, and adequate diagnostics are not always available. Human Papillomaviruses (HPV)Understanding the epidemiology of HPV has become much more important now that a clear link to cancer of the cervix has been established for some strains of the virus (Lytwyn & Sellors, 1997; Franco, 1995). Our best data come from a variety of cross sectional studies. While external genital warts caused by HPV may appear in 1-2% of young sexually active women (Sellors et al., 1992), prevalence of HPV ranges from 10-40% in studies of similar populations (Sellors, 1995). Specific molecular diagnostics for HPV are evolving and will undoubtedly assist epidemiology and research, but there is not yet a clear place for them in routine clinical care. In contrast, the early detection of dysplasia and carcinoma in situ by Pap smear has proven itself to be the most effective cancer screening program yet launched. Regardless of the role of HPV in cancer of the cervix, Pap smear and follow-up can successfully reduce mortality from that malignancy. The extent to which outcomes can be further improved by specific diagnostic and therapeutic approaches to HPV is the subject of much needed study, and Lytwyn and Sellors (1997) therefore place a high priority on research (clinical, surveillance, and behavioural) in their list of national goals for prevention of HPV infection. Genital Herpes (HSV)There is a similar paucity of Canadian data on genital herpes. Seroprevalence for Herpes simplex type 2 (by Western Blot) runs at 13-40% in the U.S. and 7-16% in Europe (Steben & Sacks, 1997). One of the few Canadian studies, on pregnant women in Vancouver, indicated rates ranging from 4.6% among women with one lifetime sex partner to 55% among those with more than ten partners (Steben & Sacks, 1997). These authors report incidence rates suggesting that annually, as many as 2% of young sexually active people may acquire the infection. Control of genital herpes will require behavioural changes among sexually active people, a clearer understanding of the cost-effectiveness of pharmacotherapy in preventing transmission, and continued work toward a vaccine. Steben and Sacks (1997) also emphasize the limited state of our national data base on genital herpes, which is not a reportable STD, and recommend a strong research effort to determine seroprevalence levels that can be used as the basis for choosing and evaluating interventon strategies. Hepatitis B Virus (HBV) InfectionTepper and Gully (1997) point out that HBV infection is the only STD for which we have a safe and effective vaccine. They cautiously suggest that reporting of "acute cases" has decreased in the 1990s and recommend a combination of programs involving immunization, contact tracing, education to reduce high risk behaviours, and condom promotion, as the basis for an effective, ongoing, public health control strategy. If we are to better understand viral STD epidemiology in general, a number of initiatives are needed. Canadian viral STD cohort studies are required to measure baseline prevalence and to establish incidence and its determinants in the population. Such studies would provide more information on viral STDs and on behavioural practices needed for prevention. Networks of sentinel clinics can also prove useful in tracking the rate of clinically evident first infections with both HSV and HPV among defined patient populations. Economic Costs of STDsThe varied health problems associated with STDs have a large impact on the cost of health care. For example, the Institute for Medicine (1996) in the U.S. estimated that costs associated with chlamydia and its complications were US$2 billion in 1994. The same report cites the expected cost of each new HIV infection to the health care system as $150,000, and this will certainly increase in the era of combination antiretroviral therapy. Currently, the annual cost to the Canadian health care system of treating people living with AIDS has been estimated at over CD$200 million (Frank, 1996). Such costs for health care and related expenditures do not begin to approximate the costs in lost income and productivity associated with AIDS or the consequence of other STD. A Conceptual Approach to STD ControlThe formula for determining the reproductive rate of a sexually transmitted disease (Ro=ßcD) is used both explicitly (Maticka-Tyndale, 1997; Patrick, 1997) and implicitly elsewhere in this issue as a tool for conceptualizing and fine tuning public health efforts to control the spread of new infection. If Ro is less than one, prevalence of infection declines over time: greater than one, prevalence increases. In this simple but conceptually useful equation: Ro = the reproductive rate of an infectious disease (i.e., the mean number of people newly infected per unit time by an individual carrying a particular STD) ß = the probability of transmission from an infected to an uninfected individual c = the number of sexual contacts per unit time between infected and susceptible individuals D = the average duration of infectivity of an infected individual. From the standpoint of epidemiology control strategies, this equation allows us to identify and assess the merits of clinical and behavioural interventions to control ß, c, and D. Clinically Based STD ControlThe approach to educing Ro with which we have had the greatest experience and the best evidence of success has been to reduce the duration of infectivity, D. This is achieved through screening, diagnosis and treatment of patients and their partners. Obviously, such an approach is best suited to managing curable STDs such as gonorrhea, chlamydia, syphilis and trichomoniasis. Indeed, in areas where STD control efforts are in place, rates of these infections have declined in a manner not yet observed for viral STDs, for which we have no curative intervention. As discussed by Patrick (1997), a more complete application of this approach to chlamydia can be expected to yield major benefits in terms of reducing incidence and costs associated with that infection, as it has done in Sweden (Westrom, 1988; Kamwendo, Forslin, Bodin, & Danielesson, 1996). As successful programs bring about decreasing incidence for a given STD, mass screening may become less cost-effective and require re-evaluation. In contrast, measures aimed at assuring identification and treatment of partners of infected individuals become more important than ever. This is already true for conditions such as infectious syphilis which is approaching low endemic levels in some parts of Canada (Romanowski, 1997). Our ability to sustain control of syphilis and other STDs depends on the maintenance of laboratory resources that can identify pathogens, determine their antimicrobial susceptibility and, where necessary, determine their molecular epidemiology. Without such capabilities, our capacity to maintain such control could be lost. Maintenance of pathogen-specific laboratory networks may be one mechanism for assuring continued access to the necessary expertise and quality control (Dillon, 1996). Behavioural Approaches to STD Control and Reproductive HealthEducational and behavioural promotion of safer sexual behaviour is a common public health strategy for prevention of HIV/STDs, cancer of the cervix, unwanted pregnancy, and other such sequelae. Changes in behaviour can reduce the reproductive rate (Ro) of an STD even when the duration of infectivity cannot be reduced because adequate treatment for that STD does not exist. The probability of transmission to each contact (ß) and the number of sexual partners (c) are the targets of most health promotion efforts in the field of reproductive health. The probability of transmission (ß) can theoretically be reduced by promotion of barrier methods and of non-penetrative sex; the number of partners by encouraging postponement or delayed onset of sexual activity, having only one partner or fewer partners overall, or abstention from high risk sexual activity. Maticka-Tyndales (1997) review points out our sometimes wishful thinking about the efficacy of some of these interventions. From a behavioural point of view, demographics may be at least partially on our side. I often remind my "baby boom" colleagues that the slowing down of this aging and highly sexually active cohort may well influence the spread of a variety of infections. Indeed, the National Population Health Survey 1994-95 (1995) indicated that of persons over the age of 30, only 6% or less reported more than one partner in the last year. This observation highlights the importance of focusing on age-specific behaviour rates. The highest burden of most STD is felt by people under the age of 25. Maticka-Tyndale (1997) shows that interventions with this group have contributed to a significant but modest movement toward safer sexual behaviour. The health promotion paradigm recognizes that more than knowledge and education is required to bring about such change. Such factors as perception of risk, self-efficacy, skills, peer pressure and other forms of reinforcemet, availability of support or materials and social context all weigh in to determine which safer choices, if any, will be embraced by an individual or a group (Green & Kreuter, 1991). Community development, as well as education and counselling, may be necessary to ensure some forms of behavioural change and, as Fisher (1997) shows, we need carefully planned evaluation to assess the effectiveness of all interventions. In practice, some behavioural parameters have proven more difficult to influence than others. Attempts to increase condom use at first intercourse have been moderately successful, and somewhat more so than attempts to initiate or maintain consistent condom use for those who are already sexually active. While Maticka-Tyndale (1997) notes the growing possibility of normative bias in reports of condom use, she also identifies promotion of condom use as the behavioural intervention with the greatest likelihood of changing behavioural patterns relevant to transmission of STD. Some of the other behavioural strategies focusing on number of sexual partners and postponing sexual involvement, etc., may also be important for getting the attention of communities at risk that are less receptive to messages that seem to stress only condom use. The principles of health promotion can and should be applied to secondary, as well as to primary, prevention. Secondary prevention refers in this context to early diagnosis and cure to prevent complications. Efforts to increase health care seeking behaviour by people at risk are particularly important, since STDs may be asymptomatic. A key corollary is the need to assure that primary care physicians are aware of and practicing according to evidence based guidelines for screening and managing STDs. Finally, all efforts to reduce transmission between individuals need not rely solely on behavioural change. Vaccines effective in preventing viral STD would be of great benefit to disease control efforts. Taking the Dragon by the TailThe metaphor of STD as a contemporary dragon is useful because it draws attention to the dragon's tail, namely, the small segment of a population that may carry a disproportionate burden of risk of infection. At the working group meeting to establish national STD goals, Robert Brunham reminded us that most of the parameters identified as risk factors for STD are not normally distributed in the population. For example, the number of lifetime sexual partners probably follows a Poisson distribution, with the majority of the population aged 15-44 at the bulging end of the distribution curve (e.g., those who have had 0-5 sexual partners), the body of the dragon, and a relatively small number at the other end (those with 6 or more partners), the tail of the dragon. Other parameters that place people at risk (poverty, homelessness, abuse, drug or alcohol addiction) may show a similar distribution. For example, the Canada Youth and AIDS Study revealed that school dropouts and street youth were likely to have had more partners and, in other ways, to be at this end of the distribution (King et al., 1990). In the same way that partner notification may be a very direct and efficient means of accessing such high risk populations, some of our behavioural interventions should also focus on those numerically small, but epidemiologically important, populations that represent "the tail of the dragon". Public policy decisions must also address the socio-economic circumstances that increasingly place the poor and disenfranchised, both domestically and internationally, at greater risk of STD. Success Stories in STD ControlHigh level control and even eradication of some STDs is not a pipe dream. Incredible successes have been achieved and others await our readiness to capitalize on todays opportunities. The decline in Canadian rates of gonorrhea and syphilis has been replicated throughout the Western world, though less evidently in the United States. The ten-fold declines over a decade in the rates of these two infections represent one of the most dramatic trends in STD epidemiology ever recorded. While the aging population and behavioural change in core groups have played a role in this trend, I think it is also true that jurisdictions with consistent STD control efforts have tended to show the most dramatic decreases. When routine chlamydia screening was introduced in Region X family planning clinics in the U.S., it was followed by a decline in prevalence among those screened from 9.3% in 1988 to 3.3% in 1994 (CDC, 1997). Dramatic reductions in the incidence of gonorrhea and chlamydia infections have correlated with impressive declines in PID morbidity and costs (Westrom, 1988; Kamwendo et al., 1996). We now have the opportunity to match this performance in Canada. Although some are sceptical of the goal of eradicating transmission of endemic syphilis, such an achievement is not without precedent. Canada no longer sees endemic transmission of chancroid or granuloma inguinale. Conclusion"A goal without a deadline is only a wish."The above was penned on the price board of a local coffee shop. It reminded me that it is important to set both goals and deadlines in the pursuit of worthwhile outcomes. Deciding when goals can be realistically reached is a crucial means of focusing resources and efforts. Catchpole (1996) has pointed out that our goals for STD prevention need to be SMART (specific, measurable, achievable, resourced, and timed). Goals must also be prioritized in terms of importance and potential impact. Given the range of laudable goals and strategies identified in the papers in this issue, prioritization will be a challenge. Some of the goals identified at the Expert Working Group meeting are listed in Table 2. They provide a basis for considering our options and potential. Since chlamydia is the most commonly reported STD and amenable to many available control efforts, it seems a prime target for public health control, with the realistic expectation of economic benefits from reduced complications such as PID and tubal infertility. Infectious syphilis is at such a low endemic level in Canada today that many believe it should be a goal to eradicate endemic cases. Efforts to achieve that goal would put pressure on travel clinics and public health structures to pick up imported cases and assure complete partner notification and treatment. Success would require that other nations have a similar priority. Although eliminating endemic transmission for gonorrhea may be a more optimistic goal, we have never been as close as we are now to achieving it. Challenges remain with genital herpes, HPV, and with the ongoing battle against HIV/AIDS. In all cases, our access to funding for public health efforts to control STD will require documentation of the cost effectiveness of preventing infection now to avoid the acute care costs of later complications. With respect to costs, we must also exmine existing practices to determine if the gains to date in some areas have won us the opportunity to become more efficient and reallocate resources. For example, audits and studies are required to determine what the impact would be of reducing some of the mass screening for syphilis and, in the future, gonorrhea, while retaining tight partner notification and outbreak control. One exciting feature about such planning for STD control is the extent to which the necessary interventions overlap with those required for other public health goals (e.g., reduction of unwanted pregnancy, cervical cancer, infertility, other reproductive health problems, etc.). Increased collaboration between STD specialists and those with mandates in other areas of sexual and reproductive health should considerably improve our ability to meet our goals. We have the knowledge and expertise in Canada, and internationally, to take informed immediate action on many of these goals and to make judicious decisions about research needed to guide and evaluate our control efforts. As I noted at the outset, we have a unique window of opportunity to realize this potential. Table 1- Organisms Commonly Transmitted by the Sexual Route
Table 2 - Proposed STD Control Goals for Canada **
References
[Previous] [Table of Contents] [Next] Last Updated: November 26, 1997 |