Published in Practical Allergy and Immunology 1995, 10(5):172-178.

The Epidemiology of AIDS in Canada

 Strathdee SA; Schechter MT.


The authors are supported by the National Health Research Development Program, Health Canada, through a Career Scientist Award granted to Dr. Schechter and through a postdoctoral fellowship granted to Dr. Strathdee.
 

Introduction:

Worldwide, the AIDS epidemic continues to spread at an alarming rate. The World Health Organization (WHO) estimates that a cumulative total of 19.5 million persons had likely been infected with HIV by January 1, 1993,¹ and on a daily basis, there are approximately 6000 new infections. By January 1, 1996, the cumulative global total of HIV infections is projected to exceed 28 million, including 7.7 million cases of AIDS.

Contrary to earlier speculation that the AIDS incidence rate was beginning to level off in Canada, recent reports indicate that the rate of newly reported AIDS cases in Canada has continued to increase for the last two years.² The most recent estimate of the cumulative number of HIV-1 infections in Canada is 42,500 to 45,000.³

It is crucial that we continue to monitor trends in the epidemiology of HIV-1 infection in Canada and develop mechanisms for measuring the impact of future public health interventions.

In this review, we will highlight current knowledge of the HIV/AIDS epidemic in Canada, focusing on AIDS surveillance data and studies of HIV-1-related mortality, prevalence and incidence among sub populations most at risk of infection. We also discuss crucial areas where data are lacking. Readers wishing to obtain an historical overview of the descriptive epidemiology of AIDS in Canada are referred to an excellent review article by Remis and Sutherland.⁴

AIDS Case Surveillance:

As of April 1995, a total of 11,192 AIDS cases had been reported in Canada.⁵

Four provinces, namely B.C., Alberta, Ontario and Quebec, have consistently accounted for nearly 95% of all Canadian AIDS cases reported since these data were first collected.⁴ The cumulative incidence rate, which refers to the total number of AIDS cases reported thus far per million Canadians, is currently 398 cases per million.⁵ Canada is deemed to be a country of intermediate incidence,⁴ and ranks fifth among industrialized nations and third among G7 nations in terms of its cumulative AIDS incidence rate.

AIDS case data is the single most commonly cited piece of information pertaining to the HIV-1 epidemic. These data are crucial for the allocation of resources for medical care, evaluating the impact of public health interventions, monitoring the changing spectrum of AIDS-related conditions in Canada, and performing trend analysis and back-calculations. While providing important information, it is important to acknowledge the various shortcomings of AIDS surveillance data. First and foremost, the number of AIDS cases at any time point is a reflection of the numbers and the characteristics of individuals who were infected with HIV many years previously, since the median incubation period for HIV infection is a decade or longer.^6,7

Second, there is a delay between the diagnosis and reporting of the case to the national AIDS database, with a median of nine months ranging to several years. This renders the number of reported cases out of date for the most recent period under consideration.⁵ The extent of delayed reporting may vary across provinces and territories. Third, under-reporting, that is failure to ever report the case, is currently thought to underestimate the total number of AIDS cases by 15-20%.⁵ Published reports from Vancouver, Toronto and Montreal suggest that under-reporting rates have not declined over time.^8,9,10,11

Recent evidence also suggests that under-reporting rates may differ according to various demographic subgroups and AIDS-defining conditions.^12,13,14

The combined effect of under-reporting and reporting delays on the number of reported AIDS cases in Canada is considerable. After adjusting for only 15% under-reporting and delayed reporting, Health Canada estimates that 16,191 Canadians had developed AIDS by the end of 1994.⁵

Another difficulty encountered when using AIDS cases to monitor the AIDS epidemic is under-diagnosis. While the extent of this problem has not been well characterized, under-diagnosis may have led to delayed treatment of HIV-1-positive women earlier in the epidemic before the gynecologic manifestations related to HIV-1 disease were well recognized.¹⁵

Under-diagnosis may still pose a problem if physicians do not recognize that the most important risk factor for HIV-1 infection among Canadian women is sexual contact with an HIV-1-infected partner. Indeed, the most recent statistics available suggest that 64% of Canadian adult female AIDS cases acquired their infection through heterosexual contact.⁵

Finally, a number of recent changes to the case definition of AIDS have impacted the extent to which AIDS cases accurately reflect trends in the epidemic. In the United States, the Centers for Disease Control (CDC) included pulmonary tuberculosis, recurrent bacterial pneumonias, and invasive cervical cancer in the CDC case definition of AIDS, effective January, 1993.¹⁶

In addition, the CDC now considers that HIV-1 infection concomitant with a CD4 cell count of less than 200 per mm³ , or less than 14% of the total lymphocyte count qualifies for an AIDS diagnosis. In 1994, Canada revised the national AIDS case definition by adopting the three new indicator diseases described above, but not the criterion concerning CD4 counts below 200 mm³ .¹⁷Acceptance of the CD4 criterion would have increased the AIDS case load by 75-80%.^18,19 Moreover, since it is well known that the measurement of CD4 cells is subject to considerable variation,²⁰ decisions to revise the case definition based on a rather arbitrary cutoff should be made cautiously. Nevertheless, changes to the case definitions of AIDS will affect comparisons of the HIV/AIDS burden between countries if differences in criteria are not taken into account.²¹

Trends in AIDS Mortality Rates:

Another means of assessing the public health impact of the HIV/AIDS epidemic is through monitoring trends in mortality. Recorded annual deaths in Canada attributable to AIDS exceeded 1300 in 1992.²²

A cumulative total of 7880 deaths among reported AIDS cases was reported through to April 1995, and approximately 70% of all reported AIDS cases in Canada are deceased.⁵ The number of lives claimed by HIV disease can only be expected to increase unless new therapeutic regimens are developed which have a dramatic effect on survival.

Recent analyses of HIV/AIDS related mortality revealed that HIV/AIDS was the leading cause of premature mortality in adult males in Vancouver, Montreal and Toronto from 1989-1992,²³ as indicated by person-years of life lost (PYLL). On a national level, male PYLL attributable to HIV/AIDS more than doubled between the period from 1987 to 1991.^23,24

More recently, it was shown that HIV-related mortality rates differed by region and gender.²⁵

Sex-specific mortality rates were significantly higher than the Canadian average in British Columbia, Quebec, and Ontario for men and in Quebec for women.²⁵

Not unlike AIDS surveillance data, statistics on mortality attributable to HIV/AIDS possess a number of limitations. It is well recognized that AIDS-related deaths are under-reported, especially with respect to underlying or antecedent causes of death.²⁶

In Quebec, it is estimated that AIDS deaths are underestimated by 10-20%.¹² Trends in mortality are also influenced by factors related to access to diagnostic and treatment expertise and must be interpreted accordingly. Studies of HIV mortality without an AIDS diagnosis in British Columbia have revealed that such deaths are more likely to occur outside of hospital, outside of a major urban center, and outside the care of a physician experienced with HIV disease.²⁷

Trends in HIV Prevalence and Incidence:

HIV-1 prevalence refers to the proportion of individuals in a given at-risk population who are HIV-infected at a particular point in time, and often includes in the numerator individuals with asymptomatic HIV infection and those diagnosed with an AIDS-defining illness. Cross-sectional studies of HIV prevalence provide a 'snapshot' of the burden of HIV-1 among various sub populations and measure the extent to which HIV-1 has spread within that population during the course of the epidemic thus far. In contrast, HIV incidence refers to the rate at which new HIV-1 infections are occurring during a specified time period. While HIV-1 incidence is much more difficult to measure, such data are invaluable since incidence is a measure of the dynamics of the epidemic in the present. The following discussion highlights the current state of knowledge of HIV-1 prevalence and incidence among various subpopulations and focuses on subgroups where data are lacking.

Homosexual/Bisexual Men:

Much information on the natural history of HIV-1 infection has arisen from studies of homosexual men. To date, two large cohort studies of gay/bisexual men have been conducted in Canada and have provided valuable data on risk behaviours, seroconversion rates, and rates of disease progression.^6,7,28

While considerable information has been collected, relatively little is known about the HIV prevalence rate and risk behaviours among subgroups of men who have sex with men, most notably men who are bisexual, young, or of various ethnocultural backgrounds. The Gay Men's Health Survey found self-reported sexual orientation to vary by region, but in general, 10-15% of men interviewed at venue-based locations across Canada self-identified as bisexual.²⁹

These data underscore the need for more research on bisexuals, since it has been established that bisexual men may be more likely to engage in high-risk sexual activity,³⁰ are less likely to have been tested for HIV-1,³¹ and have not been specifically targeted for public health prevention strategies apart from efforts in their own community.

To date, Canadian studies of homosexual men have included few young gay men. The mean age of gay men at study entry in the Vancouver Lymphadenopathy AIDS Study (VLAS) and the Toronto Sexual Contact Study, both of which were launched in the early 1980s, was 33 years.^32,33

Results observed in these studies may not be generalizable to the younger generation of gay men. Moreover, recent evidence from the United States suggests that the annual incidence rate among gay men aged 18-25 is 2-3% per year,³⁴ which concurs with a recent estimate of seroconversion among men having sex with men in all age groups in Ontario between 1990 and 1994.³⁵

Although in the latter study it must be conceded that self-referral for HIV testing could have introduced a selection bias, if similar rates of seroconversion exist in other provinces, it follows that thousands of new infections among gay/bisexual men are now occurring on an annual basis.

There is also a need for further study of the complex inter-relationships between race, poverty and HIV disease among populations at high risk of infection. An American study has suggested that young gay men of Black or Hispanic origin are much more likely to become infected with HIV-1.³⁶

A Canadian study suggested that gay men who continued to engage in high risk taking behaviour were more likely to be younger, smoke cigarettes and use nitrate inhalants, and earn less than $10,000 per year.³⁷ This led to the finding of a clear relationship between lower socioeconomic status and more rapid mortality among homosexual HIV-infected men.³⁸

These findings suggest that public health interventions which impact upon socioeconomic factors could influence both rates of HIV-1 infection and progression to disease.

Intravenous Drug Users and Prison Populations:

There is grave concern about the escalating rates of HIV infection in the injection drug using (IDU) population in Canada. In Montreal, ongoing studies have monitored HIV-1 prevalence and incidence rates among attenders of the CACTUS needle exchange³⁹ and among IDUs in the St-Luc Hospital open cohort.⁴⁰

Prior to 1988, HIV-1 prevalence rates among IDU in Montreal were less than 5%.⁴ Yet among CACTUS needle exchange attenders, HIV-1 prevalence rates rose to 15.2% in 1991, 16.4% in 1992, and appeared to stabilize at 15.6% in 1993.³⁹ Bruneau et al⁴¹ have shown that the association between needle exchange attendance and HIV seroconversion is strong and consistent. Although HIV incidence among this group has fallen from 13.8 per 100 person-years in 1990 to 5.3 per 100 person-years in 1993, the cumulative incidence rate of 9.8 per 100 person-years over this four-year period is among the highest in North America.³⁹

Further research is clearly required to interpret these data, in light of the positive impact needle exchanges have demonstrated throughout the world. For example, there is no evidence to suggest that needle exchanges lead to increased drug use, nor has the median age of first injection decreased among attenders in other cities.⁴²

Since it is well known that IDUs who demonstrate good compliance with respect to needle-sharing behaviours are less likely to maintain safer sex practices, there is an urgent need to uncover possible confounding factors and interactions between exposure variables among attenders and non-attenders of needle exchange programs in Montreal and other cities. A deeper understanding of the availability of sterile injection equipment and barriers to clean needle use is also required.

On a national level, HIV-1 prevalence rates among IDU populations vary widely by region. Following a period of relatively stable seroprevalence rate in 1991 and 1992 in Toronto where HIV-1 prevalence was 4.5% and 4.8% respectively,⁴³ prevalence rose to 7.6% during the period from 1993 to 1994.⁴⁴ This trend was partially attributed to higher infection rates among male IDUs who reported having sex with other males. In contrast, Calgary and Winnipeg have reported rates of 1.9%⁴⁵ and 2.3%⁴⁶ respectively. In British Columbia, the prevalence of street-involved IDUs appeared relatively stable between 1988 and 1992, with an overall prevalence of 3.2%.⁴⁷ However, a large increase in the number of IDUs testing HIV-positive has prompted a case-control investigation.⁴⁸

Although no recent estimates of HIV-1 prevalence are available, the proportion of IDUs testing HIV-positive in the province has risen to 6% since January, 1993.⁴⁹

There is also concern regarding the potential for HIV transmission within Canadian provincial and federal prisons, where bleach and condoms are not readily available and there is no access to sterile injection equipment despite the widespread use of drugs.⁵⁰ Generally speaking, HIV prevalence rates among incarcerated populations are often directly related to the proportion of inmates who report IDU.^50,51

As early as 1989, HIV prevalence rates in Quebec federal prisons among females and males were 7.7% and 3.6%, respectively.⁵² In 1993, an anonymous unlinked study of leftover urine in Ontario provincial jails reported HIV prevalence rates of 2.2% for females and 0.99% for males.⁵³ In British Columbia, a voluntary seroprevalence study of provincial prisons in 1993 found HIV prevalence rates of 3.3% among women and 1.0% among men.⁵⁴

Since HIV transmission within the correctional setting has been documented in the literature,⁵⁵ there remains an urgent need for harm reduction programs for inmates which are coordinated with the communities to which they will return.^50,51

Aboriginal Populations:

Very little is known about HIV-1 infection rates among Aboriginal peoples. While only 116 AIDS cases among Aboriginals have been reported in Canada (personal communication, Dr. M. Ricketts, May, 1995), there is some evidence to suggest that AIDS underreporting rates may be higher than expected among this population.¹⁵ Among reported Aboriginal AIDS cases, it has been noted that a higher proportion is attributable to IDU compared to non-Aborignal AIDS cases.⁵⁶ Only a few HIV-1 prevalence estimates are available among the Aboriginal population. Based on self-reports of HIV-1 antibody test results, the Ontario First Nations Healthy Lifestyle Survey estimated that between 0.12% and 1.4% of on-reserve Aboriginals may be HIV-infected.⁵⁷

In this survey, Calzavara et al reported that 84% of respondents who reported having sexual partners both on and off reserves had recently engaged in unprotected sex.⁵⁸ Knowledge of HIV-1 transmission was less satisfactory among Aboriginals who were familiar with traditional ways.⁵⁷ HIV-1 seroprevalence among street-involved Aboriginals in Vancouver ranged between 2-8% from 1988 to 1993.⁵⁹

Yet by the end of the first quarter of 1995, 12% of incident HIV infections verified by the British Columbia Centre for Disease Control were among persons of Aboriginal descent.⁶⁰ In northern Alberta, the number of new HIV-positive clients in medical clinics who identify as Aboriginal is steadily increasing, and CD4 cell determinations suggest that these infections are more likely to be recent.⁶¹

Growing evidence of a burgeoning HIV-1 epidemic in the Aboriginal population suggests that culturally sensitive prevention strategies are required.

Women of Child-bearing Age:

In an attempt to monitor HIV-1 prevalence among the general population, studies have been conducted among three groups: women of childbearing age, attenders of STD clinics, and patients providing routine specimens in sentinel clinics or hospitals. Anonymous, unlinked seroprevalence studies have been conducted to date among women of childbearing age in 7 provinces and territories. The latter have typically utilized leftover blood from routine antenatal testing or leftover blood from neonatal heel pricks. Rates have ranged from:

• 0.0 in PEI⁶² and Manitoba⁶³
• 1.0-2.0 per 10,000 population in Nova Scotia⁶⁴
• 2.20 per 10,000 in Ontario⁶⁵
• 4.95 per 10,000 in British Columbia and the Yukon⁶⁶
• 6.25 per 10,000 in Quebec⁶⁷
• and 8.70 per 10,000 in Newfoundland.⁶⁸

The relatively high seroprevalence rate among women in Newfoundland led to the identification of a cluster of 31 HIV-positive women in the rural Eastern township of Newfoundland (personal communication, Dr. Catherine Donovan, March 1995). This indicates that even if overall HIV prevalence is low in a given area, there remains the potential for clusters of infections to occur in both rural and urban communities. Moreover, it is well known that relatively stable seroprevalence rates over time can mask increasing seroincidence.⁶⁹

It is important to recognize selection biases inherent in studies of women giving birth to live infants. Among women undergoing abortion in Quebec, a crude HIV prevalence of 2.0 per 1,000 was observed, but rates were significantly higher among women born in Pattern II countries where HIV infection is endemic.⁷⁰

These results emphasize the fact that subgroups of the heterosexual population, which may include ethnocultural minorities, may be at high risk for HIV infection.

General population studies:

In an attempt to avoid selection biases common among HIV-1 prevalence studies, two provinces, Quebec and British Columbia, have performed anonymous, unlinked HIV-1 prevalence studies using specimens submitted for routine medical testing. In B.C., HIV-1 testing was performed on discarded blood specimens obtained from two large community-based medical laboratories in early 1993. After attempting to exclude repeat specimens from the same individuals, this study reported an overall HIV-1 seroprevalence rate of 93.0 per 10,000 for men and 7.4 per 10,000 for women aged 15 to 55 in the greater Vancouver region.⁷¹

In Quebec, Alary et al⁷² calculated HIV prevalence based on specimens from sentinel hospital outpatient departments between 1990 and 1992. During the study period, HIV-1 prevalence estimates in the city of Montreal alone increased from 7.8 per 10,000 to 17.7 per 10,000 for males, while rates were relatively stable between 1.0-2.0 per 10,000 for females.

Finally, sentinel surveillance of STD clinics has provided useful HIV-1 prevalence data. Estimates are very similar for clients presenting for syphilis testing at STD clinics in 1991 and 1992 in Ontario⁷³ and in B.C. during 1991 and 1992.⁷⁴

In these studies, HIV-1 prevalence was estimated to be 0.2% for females and approximately 4% for males. Since it is well established that STDs are useful proxy measures of unsafe sexual practices and may also promote HIV-1 transmission, prevention efforts which target high risk populations such as attendees of STD clinics could directly impact upon HIV-1 incidence rates. Studies attempting to determine HIV-1 incidence based on data from repeat attenders could prove to be an excellent means of tracking the HIV epidemic in the future.

Summary:

The HIV epidemic in Canada is best considered as a series of overlapping epidemics with different times of onset, which becomes increasingly more complex as it matures. The peak of HIV infection among men having sex with men likely peaked in the early to mid-1980's, but there remains concern that young gay and bisexual men may continue to engage in behaviours which place them at high risk of infection. Recent evidence suggests that infection rates in this group could be rising. The current situation among IDUs is alarming. Since Montreal appears to have one of the highest seroincidence rates in North America,³⁸ new interventions and further research in this city and other Canadian epicentres should be a high priority. Future research which focuses on other marginalized populations such as prisoners and ethnocultural communities is also required. Much more information about the determinants and the dynamics of HIV-1 in First Nations people is urgently required. Given the current situation among IDUs in Canada, the potential for increased heterosexual and perinatal transmission is also of concern. Across the world, no community or country which has reported even one AIDS case can claim that the spread of HIV has been halted.¹

As noted above, knowledge of the spread of HIV-1 today is difficult to attain. But there is little doubt in considering the available incidence data that several thousand new infections are continuing to occur in Canada on an annual basis. For those policy makers who are primarily motivated by cost considerations, it is worthwhile noting that each 1000 of these new HIV-1 infections adds approximately $100 million to our collective future direct medical costs and approximately $0.6 billion in indirect costs, primarily through lost productivity.⁷⁵ If you are a politician or taxpayer who naively believes that AIDS is not your problem, ask not for whom the bell tolls; it tolls for thee.

Acknowledgements:

The authors are supported by the National Health Research Development Program, Health Canada, through a National Health Research Scientist Award granted to Dr. Schechter and a postdoctoral fellowship granted to Dr. Strathdee. We gratefully acknowledge Drs. Robert Remis, Michael O'Shaughnessy, and Robert Hogg for critical appraisal of the manuscript, and Elizabeth Ferris for secretarial support.

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Bonnie Devlin
Vanguard Project Coordinator
608 - 1081 Burrard Street
Vancouver, BC, Canada, V6Z 1Y6
Tel: (604)806-8306
Fax: (604)806-9044