Control of sexually transmitted disease : The Canadian perspective

The ability to control a disease depends on knowledge of 
its epidemiology. Such information on sexually transmitted diseases (STDs) can be ascertained 
by surveillance data involving the analysis of notification reports, as well as laboratory reports, 
hospital discharge data, and data from sentinel clinics and health units. In the case of sexually 
transmitted hepatitis B, notification data will probably have to be corroborated by data from 
sentinel clinics, health units or physicians. A vigorous attempt must be made to elucidate the 
mode of transmission in acute cases and newly discovered carriers. Appropriate treatment, 
contact tracing and primary prevention strategies appear to have had some success in 
controlling gonorrhea and syphilis. Rates of genital chlamydial infection may also be reduced 
by the same methods. These diseases will, however, persist in certain 'core groups'. Control of 
sexually transmitted hepatitis B will require a primary prevention strategy of risk reduction, 
sexual health promotion and immunization. Targeted immunization programs on their own 
are not Likely to work. Thus, universal immunization will probably be required along with public 
acceptance of immunization against STDs and appropriate human and financial resources. 
Reliable surveillance data will be required for program evaluation.

I N TH E PAST.PROGRAMS TO CONTROLSEXUALLY trans- mitted diseases (STDs) in Canada were directed at gonorrhea and syphilis.Du ring the 1980s, genital chlamydia!infections became important fo r their long and short term consequences.In addition.h uman immunodeficiency virus (HIV) infection and the acquired immu ne deficiency syndrome (AIDS) became the predominant STD in the public's eye.Only a small n umber of cases of chancroid, another 'traditional' STD.exist today.Hepatitis B. on the other hand, has yet to be widely recognized as a 'm ainstream' STD.
Although the control of commun icable diseases in Canada is primarily a provincial and ten i torial responsibility.the federal government also plays an important role.For examp le. the mandate of the Laboratory Centre for Disease Control (LCDC) -a directorate of the Health Protection Branch (HPB) of Health and Welfare Canada -is to be the national centre fo r preserving and improving public health through the identification , investigation .control and prevention of dis eas e in h umans .The data and information produced by the LCDC are used for improving disease control (both communicable and chronic) , planni ng and policy developm ent.and educating the public.The quality of these data a re important when used to assist national, provincial and territorial strategy formulation .eg, in the area of immunization.
The LCDC includes the Bu rea u of Communicable Disease Epidemiology.the Burea u of Chronic Disease Epidemiology and the Bureau of Microbiology.
The Divis ion of STD Control.under the Bu reau of Communicable Disease Epidemiology.is responsible for national surveillance of STDs (excluding HIV/ Al DS).epidem iological research related to STDs. and the provision of support for control programs.To a chieve the latter, guidelin es a re being developed for the m an agement of STDs and interprovincial liaison is being promoted .Furthermore, the Nation al Laboratory fo r Sexu ally Transmitted Disease (Bureau of Microbiology) has a close relationship with the Division of STD Control.The Federal Centre for AlDS is a separate directorate within the HPB.

SURVEILLANCE
Knowledge of the epidemiology of diseases is vital to the development a n d evalu ation of disease control strategies .Surveilla n ce. the object of which is to produce accurate epidem iological data, is as im portant in controlling STDs as it is in controlling other communicable d iseases.
Surveillance data are derived from notifiable commu n icable disease reports by physicians to medical officers of heal th and then to provincial/ territorial authorities who forward da ta n ationally.In addition, la boratory reports.hospital discharge data and, to some extent.data from sentinel clinics and h ealth u nits h ave been u sed.

NOTIFICATION REPORTS
Up until the mid 1940s.the reported ra tes of syphilis a nd gonorrhea were similar (Figure 1).Although gonorrhea rates outstrip ped those of syphilis at the end of World War II. the rates of both diseases dropped with the adven t of antimicrobial therapy and better control.Rates of syphilis have remain ed comparatively low since the early 1950s.Rates of gonorrhea .on the other hand, plateaued in the 1950s , rose sharply in the late 1960s and fell markedly during the 1980s.
In recent years.it appears that gonorrhea and

U E
syphilis have been controlled fot a variety of reasons.These include a dequate treatment a n d contac t tracing as well as primary preven tion efforts in groups with high risk beh aviours -the latter being s purred by the AIDS epidemic.Despite the marked decline in reports of gonorrhea in persons aged 15 to 24 years.there h as been an overall increase in the percen tage of cases occurring in this age grou p.The increased threat of a ntimicrobial-resistant Neisseria gonorrhoeae h as been masked by the continued fall in overall numbers of cases .Genital chlamydia reporting rates have only recently become available n ationally and are therefore somewhat difficu lt to interpret.Reported rates in certain provi nces a nd territories such as Manitoba and Alberta, and the Yu kon , however.may be quite accu rate.Rates a ppear to be plateau ing and even starting to drop in p rovinces with the highest rates initially.This may be du e to better control of genital ch lamydia!infection with appropriate treatment.contact tracing and screening.
It s hould be noted , h owever .rates of gonorrhea and eventually genital ch lamydial infections ,vill most likely stop falling.p lateau , and then persist in core grou ps of 'high transmitters•.These groups become the main reservoir of d isease, including antimicrobial-resis tant gonorrhea .Con trol efforts including prevention strategies for these groups are u nfortunately difficult.
When used as a mea ns of identifying sexu ally transmitted hepatitis B. notification reports give rise to a number of problems such as : consistency.especially when increased interest in the disease leads to increas ed reporting; low sen sitivity or u nderreporting; and low s pecificity.Specificity becomes an issue particularly with h epatitis B if repo rts of acute cases and carriers are not separated.Use of the n otification proces s to survey s exually transmitted h epatitis B would requ ire careful assessment of this mode of transmission.Th e primary care physicia n or thos e involved in fo llowing up notifications of com mu nicable disease at the local public h ealth a u tho ri ty level, would h ave to investigate each cas e with vigou r.Th e traditional notification system.however. is n ot des igned to collect complete data of this kind .Although s u ch data collection may become possible with the implemen tation of n ational case-bycase reporting.the system s till relies on the com pleteness of data collected at the health unit level.

LABORATORY REPORTS
Most p rovi n cial notification system s rely on positive laboratory reports to j ustify inclu sion of a case.The only data available.at least n ationaJly.on n on-notifiable STDs (in cluding genital herpes and.unW recently.genital chlamyd ia) have been reports from la boratories wh ich agreed to supply data (1).Th ese data are in evita bly biased as they are only based on reports from particula r la boratories.Laboratory reports of chlamydial infec tion give a cru de idea of the age distribution of cases and a distorted view of the sex ratio.A review of laboratory reports of h epatitis B markers would be similarly biased .Use of these data would requ ire clinical and epidemiological information .which is unlikely to be availa ble. at least routinely, to la boratories.

HOSPITAL SEPARATIONS
Hospital disch a rge data have been found to be useful for evaluating STDs with long term consequen ces -most importa ntly for genital chla mydial inJection.Hospital separation rates for pelvic infla mmatory disease (PIO) can provide useful inform ation, bearing in m ind that data are not available over a long period of time and are complicated by the fact that older coh orts may h ave su ffered PIO as a result of other STDs a part from chlamyd ia .Hospital separation data on ectopic pregna ncies (Figure 2) .h owever, con fi rm a cum u la tive effect of PIO causing tu bal sca rring.which ca n be directly linked to the prevalen ce of genital chlamydial infection.The use of hospital disch arge data for hepatitis B surveillance would require adm ission not on ly for the disease bu t also for the long term consequ ence of disease or for a nother specific diagnosis s uggesting hepatitis B infection.

SENTINEL CLINICS
Reporting from sen tinel clinics , h ealth units or physicians will probably be a usefu l adjunct to surveillance if trends in sexually tra nsm itted hep-llA USE a litis l3 are to be followed.Sen tinel clinic data have been u sed by the National Laboratory fo r STD (2) and the Division of STD Control (un publis h ed data) .However.there are difficulties in extrapolating these kinds of data.For example.STD.s tudent h ealth, adolescent and family planning clinics all see selected populations.each with its own hepatitis B risk.The mode of transmission of hepatitis B wou ld have to be assessed by health care providers participating in sentinel surveillance.
Thus. there are several m eans of acquiring surveillance data on STDs.However. the use of these alone to a scertain trends in sexual transmission of hepatitis B is problem atic, except for perhaps sentinel clinics.health units or sentinel ph ys icia ns.Fu rthermore.n oti fication data are useful but should be corroborated by other means.

CONTROL OF SEXUALLY TRANSMITTED HEPATITIS B
The control of gonorrhea, syphilis.and perhaps chlam ydia in part.h as been due to a nu mber of factors: a dequa te testing.treatment.screening for asymptomatic cases and p rimary prevention.The thrust for p rimary prevention.including promotion of sexual health .use of condoms and limitation of the number or sexual partners .was boosted the dvent of HIV infection and AIDS.The drop in rates of gonorrh ea and syphilis can u ndoubtedly be explain ed in part by the changes in risk behaviour of the m ale h omosexual community.However.influencing the h igh risk behaviour of adolescents and young adults -especia lly of those who are poor and living on the street -has been m u ch less successful.
For controlling hepatitis B. one clear advan tage is the availability of immu nization .Disa dvan tages are the la ck of treatment and the h igh percentage of asymptomatic cases (3).Immu niZation would control the disease regard less of its mode of transmission.and programs could be targeted at h igh risk groups or they could be universal.Evaluation of immun ization programs for effectiveness would be required.especially in times of economic res traint.
To control h epatitis B with immunization , sev-12A Y•DO OTCGn era! issues need to be add ressed.These inclu de the availability of fun ding for the targeting of specific risk-behaviour grou ps and even the ability to access these groups.With respect to u niversal immunization programs.the delivery systems for childh ood and adolescent immunization are already in place.However.public acceptance of s u ch a preventive measure fo r an STD is u ncertain, as mos t paren ts identify universal immunization programs with childhood disease only .Furthermore, adequate fu nding from provincial and territorial governments is an important consideration.

SUMMARY
STDs can be con trolled usi ng primary prevention strategies together with s pecific treatment, con tact tracing and screening efforts .Control of hepatitis B depends on the availability of an immunization program for those a t risk of hepatitis B as an STD.Such a program must be affordable to the provinces.publicly acceptable and evaluated with s m v eillance data.Prevalen ce and incidence data will a ls o be required to m ake both health care providers and t he public aware tha t hepatitis B is an STD and a n important cause or morbidity and perhaps mortality.
These steps must take place prior to.or at least s imu ltaneously with, discussions of scheduling.vaccine dosage and the need for boosting.A good vaccine is useless without the money to deliver it lo those at risk.