Prevalent HIV Infections in Canada: Up to One-Third May Not Be Diagnosed

At A Glance

There were an estimated 49,800 people living with HIV infection in Canada at the end of 1999.

Of these, approximately 15,000 or 30% are not aware of their infection.

Given the new treatments for HIV, it is more important than ever that all Canadians are able to access HIV testing.

HIV/AIDS EPI Updates

April 2003

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Prevalent HIV Infections in Canada: Up to One-Third May Not Be Diagnosed

Introduction

This Epi Update presents the estimated number of Canadians who were HIV-infected but unaware of their infection at the end of 1999. It also summarizes available data on the characteristics of persons tested for HIV in Canada. It is anticipated that the next set of national estimates will pertain to the year 2002 and will be produced during 2003.

HIV Testing in Canada

Knowledge of one's HIV status can be useful for several reasons. Counselling received at the time of HIV testing can provide critical information about how to reduce the risk of HIV infection. If an individual is found to be HIV infected, consideration can be given to starting antiretroviral therapy. In the case of pregnant women, treatment can reduce the chances that the infant will be infected from about 25% to 8% or less.¹

Canadians have had the opportunity to be tested for HIV infection in Canada since the test became available in 1985. Individuals have accessed HIV testing services through either coded or confidential testing at a doctor's office or clinic, or through anonymous testing sites.

Positive HIV test report data are provided by all provinces and territories in Canada to the Centre for Infectious Disease Prevention and Control (CIDPC) and are presented in the most recent semi-annual report: HIV and AIDS in Canada: Surveillance Report to December 31, 2001.² They are based on non-nominal, confidential HIV testing information with duplicate tests for the same individual removed to the extent possible. The removal of duplicates is necessary to accurately reflect the annual number of new HIV diagnoses. Duplicate removal rates vary by year, province and type of data (nominal, non-nominal or anonymous). It is important to note that in most provinces, the ability to remove duplicates has improved significantly since 1995

HIV-Infected but Unaware

There have been approximately 46,000 positive HIV tests reported to CIDPC to December 31, 1999.³ After adjusting for under and delayed reporting, it is estimated that about 51,000 Canadians have tested positive for HIV from 1985 (when testing became available) to the end of 1999. Of this total, an estimated 15,000-17,000 individuals had died by the end of 1999 (also adjusted for under and delayed reporting). Therefore, of this 51,000 approximately 34,000-36,000 individuals were aware of their HIV infection and were still alive at the end of 1999.

It is important to note that data on positive HIV tests only represent those who have tested positive for HIV infection and do not represent all persons who have been infected with HIV as some individuals who have been infected with HIV have not yet come forward for testing.

In November 2000, CIDPC published estimates of HIV prevalence in Canada to the end of 1999.⁴ It was estimated that approximately 49,800 Canadians were living with HIV infection (including those living with AIDS) at the end of 1999. This number includes those who are aware of their infection (had a positive HIV test) and those who are unaware of their infection.

The difference between the total number who were HIV-infected and alive at the end of 1999 (49,800) and the number who were aware of their HIV infection and alive (34,000-36,000) at the end of 1999 represents an estimate of the number of persons unaware of their infection (not yet tested positive for HIV) and alive. This difference is approximately 15,000 or about 30% of the estimated 49,800 Canadians living with HIV infection at the end of 1999.

Characteristics of Persons Tested for HIV

A Canada-wide survey conducted in January 1997 found that 18.6% of men aged 15 years and older and 16.2% of women aged 15 years and older had been tested for HIV (excluding tests for blood donation and insurance purposes).⁵ Of those tested, 39% had been tested in the year prior to the survey, 57% in the prior 2 years, and 43% had their most recent test more than 2 years prior to the survey. A 1996 survey found that, taking into account ancillary testing such as donating blood or being tested for life-insurance purposes, 41% of men and 31% of women in Canada had ever been tested for HIV.⁶

National surveys of the general population suggest that those who report risk factors are more likely to be tested:

• Among heterosexuals, those with two or more partners in the last year were more likely to be tested than those with one partner (50.5% vs 17.4%). Of those who reported having had a sexually transmitted disease (STD) in the past 5 years, 58% had been tested compared to 17.4% of those who did not report an STD.⁵

• For men, testing was higher among those who had sexual intercourse with another man (71%), used injecting drugs (62%), received blood or clotting factor between 1978 and 1985 (27%), or had a partner with a risk factor (IDU, having received blood or clotting factor between 1978 and 1985, origin in from country endemic for HIV) (30%).⁵ For women, testing was higher among those who had received blood or clotting factor between 1978 and 1985 (32%), had a high-risk partner (38%), or had sexual intercourse with a man since 1978 (17%).⁶

• Testing is highest among individuals aged 25 to 34 years. Even after taking into account all other risk factors, those aged>= 45 years are still less likely to be tested than are those < 45 years.^5,6

• Although those reporting risk factors such as IDU, multiple partners, or MSM are more likely to be tested, a substantial proportion of those reporting risk factors have not been tested recently, or have not been tested at all. For example, among those who report more than one partner in the last year and not using condoms consistently, 53% of men and 38% of women have never been tested.⁵

Comment

Canadians with risk factors for HIV infection are more likely to have been tested for HIV than those without such risk factors. However, there is still a significant proportion of persons with risk factors who have never been tested for HIV. It has been estimated that there are approximately 15,000 people or 30% of the HIV-infected population who are unaware that they are infected. More information is needed about individuals who are at risk for HIV, but who have not been tested. Given these data, and the fact that new treatments are available for HIV infection, it is more important than ever that all Canadians be able to access HIV testing, particularly those at highest risk for HIV infection.

References

1. Mofenson LM, McIntyre JA. Advances and research directions in the prevention of mother-to-child HIV-1 transmission. Lancet 2000;355:2237-44.

2. Health Canada. HIV and AIDS in Canada: Surveillance Report to December 31, 2000. Division of HIV/AIDS Epidemiology and Surveillance, CIDPC, PHAC, Health Canada, April 2001.

3. Health Canada. HIV and AIDS in Canada: Surveillance Report to December 31, 1999. Division of HIV/AIDS Epidemiology and Surveillance, CIDPC, PHAC, Health Canada, April 2000.

4. Geduld J and Archibald C. National trends of AIDS and HIV in Canada. CCDR 2000;26:193-201.

5. Houston SM, Archibald CP, Sutherland D. Sexual risk behaviours are associated with HIV testing in the Canadian general population. Can J Inf Dis 1998, 9 (Suppl A): 39A, #239P. And unpublished data from: Canada Health Monitor survey, January 1997, Division of HIV Epidemiology, LCDC, Health Canada.

6. Houston SM, Archibald CP, Strike C, Sutherland D. Factors associated with HIV testing among Canadians: Results of a population-based survey. International Journal of STD and AIDS 1998; 9:341-346.

For more information please contact:

Division of HIV/AIDS Epidemiology & Surveillance Centre for Infectious Disease Prevention & Control Public Health Agency of Canada Tunney's Pasture, Postal Locator 0900B1 Ottawa, ON K1A 0L2 Tel: (613) 954-5169 Fax: (613) 946-8695

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