This Epi Update presents information on the estimated number of Canadians who were HIV infected but unaware of their infection at the end of 2008. It also summarizes available data on the characteristics of people tested for HIV in Canada.
It is important to note that data on positive HIV tests represent only those who have tested positive for HIV infection and do not represent everyone who has been infected with HIV, as some who have been infected have not yet accessed testing. The Centre for Communicable Diseases and Infection Control (CCDIC) recently published estimates of HIV prevalence in Canada to the end of 2008 (for details, please see Chapter 1 of this Epi Update series, entitled "National HIV Prevalence and Incidence Estimates in Canada for 2008").
It was estimated that approximately 65,000 (54,000-76,000) Canadians were living with HIV infection (including those living with AIDS) at the end of 2008. This number includes those who were aware of their infection (had had a positive HIV test) and those who were unaware of their infection (had not been tested for HIV yet or had not known their testing result). There have been 67,442 positive HIV tests reported to CCDIC since testing began in November 1985 to December 31, 2008, which translates to about 70,400 after adjusting for underreporting and duplicates. Of these, we further estimated that approximately 22,300 have died. Thus, there were an estimated 48,100 (70,400 minus 22,300) Canadians living with HIV infection in 2008 who had been given a diagnosis of HIV (tested positive) and were therefore aware of their HIV status. Since an estimated total of 65,000 people were living with HIV in Canada in 2008, the remaining 16,900 (range of 12,800- 21,000), or 26% of prevalent cases, were unaware of their HIV infection. This figure is slightly less than the estimate of 27% who were unaware of their HIV status in 2005.
The estimated percentage of people living with HIV who are unaware of their HIV status varies by exposure category. Approximately 19% of infected people in the MSM (men who have had sex with men) exposure category and 25% of those in the IDU (people who inject drugs) exposure category are unaware of their HIV infection. By comparison, there is a much higher proportion of individuals (35%) who are unaware in the combined heterosexual exposure category (Figure 1). These percentages correspond to an estimated 6,000 (4,500-7,500) MSM, 2,800 (2,000-3,600) IDU and 7,000 (5,200-8,800) people in the combined heterosexual exposure category who were unaware of their HIV-positive status at the end of 2008.
A more direct measure of the proportion of people in certain subpopulations who are HIV infected but unaware of their infection is available through the national, second- generation HIV surveillance systems. This is possible by comparison of self-reported HIV status (by questionnaire) with HIV serostatus, measured by the biological specimen obtained from participants. Using this methodology, the "unaware" individuals were survey participants who reported that they had never been tested for HIV or that their HIV status was negative or unknown, whereas HIV testing performed on their biological specimens indicated that they were HIV positive. In the I-Track, the surveillance system focused on people who inject drugs, the overall proportion of participants with HIV-positive specimens who were unaware of their positive status was 22.3% in Phase 1 (sentinel site range: 11.1% to 50.0%, surveys conducted in 2003-2005) and 21.0% in Phase 2 (sentinel site range: 0.0% to 43.5%, surveys conducted in 2005 to 2008). In the M-Track, the surveillance system focused on gay, bisexual and other MSM, the overall proportion of HIV infected participants who were unaware of their HIV positive status was 19.1% (sentinel site range: 12.5% to 23.2%).
For more details on the "Track" second-generation HIV surveillance systems, see Chapter 3 of these Epi Updates , "HIV Testing and Surveillance Systems". Chapter 9, "HIV/AIDS among Gay, Bisexual and other Men who have sex with Men (MSM) in Canada", provides more information on the epidemiology of HIV and AIDS among MSM, and Chapter 10, "HIV/AIDS among People Who Inject Drugs in Canada", provides information on HIV infection among IDU.
Despite the widespread availability of antiretroviral treatment and extensive promotion of HIV testing, an estimated 26% of HIV infections remained undiagnosed in Canada in 2008. The situation is very similar in other high-income countries. For example, the percentage of HIV-positive people without a diagnosis was estimated to be 21% in the United States in 2006,Footnote 1 30% in the European Union in 2008Footnote 2 and 27% in the United Kingdom in 2008.Footnote 3 We estimated that among MSM in Canada, 19% of people living with HIV were unaware of their HIV positive status, which is comparable with a recent report (20%) from Australia,Footnote 4 slightly lower than the rates estimated in the US (23.5%)Footnote 5 and the UK (26.9%)Footnote 3 , and much lower than the rate from a survey in Scotland (41.7%).Footnote 6 We estimated that among IDU in Canada, 25% of people living with HIV were unaware of their HIV status, which is very similar to recent estimates in the UK (25.5%)Footnote 3 but higher than estimates in the US (14.5% of male IDUs and 13.7% of female IDUs).Footnote 5 Our estimate of 35% in the heterosexual exposure category is slightly higher than the rate estimated in the UK (27.1%)Footnote 3 and the US (26.7% of men and 21.1% of women).Footnote 5
HIV testing first became available in Canada in 1985. Since then, individuals have had the opportunity to access HIV testing services through either nominal or non- nominal testing at a doctor's office or clinic, or through anonymous testing sites available in some provinces. At present, nominal/name-based and non-nominal/non- identifying HIV testing methods are widely available in Canada; however, anonymous HIV testing is available in only seven provinces (for details, please see Chapter 3, entitled "HIV Testing and Surveillance Systems").
There has been no new Canada-wide survey available regarding HIV testing behaviour since 2003. A Canada- wide survey conducted in March 2003 of randomly se- lected individuals above 15 years of age revealed that just over one-quarter (27%, 29% of men and 24% of women) reported ever having been tested for HIV, excluding testing for the purposes of insurance, blood donation and participation in research.Footnote 7 The figures from this 2003 survey show that a higher proportion of individuals reported having been tested than in a January 1997 Canada-wide survey, which found a corresponding figure of 18.6% of men and 16.2% of women aged 15 years and older (excluding tests for blood donation and insurance purposes).Footnote 8 Footnote 9 However, the proportion of people who had been tested in the previous 2 years did not increase (42% in 2003 and 57% in 1997). The results of a 1996 survey showed that, taking into account ancillary testing such as for blood donation or life insurance purposes, 41% of men and 31% of women in Canada had ever been tested for HIV.Footnote 10
National surveys and studies of the general population suggest that those who report risk factors are more likely to be tested:
It has been estimated that approximately 16,900 people or 26% of the HIV-infected population were unaware that they were infected at the end of 2008. The size of the undiagnosed group is especially difficult to estimate because, without testing, those individuals are "hidden" to the health care and disease monitoring systems. It is important to reach this group since individuals whose infection has not been diagnosed are unable to take advantage of available treatment strategies or appropriate counselling to prevent the further spread of HIV. The transmission rate in the undiagnosed group is likely higher than that of the tested and diagnosed group.Footnote 18 Studies have found that the frequency of high-risk sexual behaviour was reduced substantially after HIV diagnosis.Footnote 19 To help stem the HIV/AIDS epidemic, it is important to increase the number and proportion of people living with HIV who receive testing and are informed of their serostatus.Footnote 18
HIV testing is important not only for prevention and control measures but also for the benefit of the individuals who are tested. 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 HIV negative. 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 35%-40% to 2% or less.Footnote 20
People at high risk of HIV (such as MSM or IDU) more frequently test for HIV, but scaled-up and targeted promotion of HIV testing is still needed in certain subpopulations that access testing less frequently (such as younger individuals and those with lower income and lower education levels). In order to better inform interventions, further information is needed about individuals who are at risk of HIV but have not been tested. Given the findings to date and the fact that new treatments are available for HIV infection, it is more important than ever that all Canadians, particularly those at highest risk of infection, should be able to access HIV testing.
For more information, please contact:
Surveillance and Risk Assessment Division
Centre for Communicable Diseases and Infection Control
Public Health Agency of Canada
Postal locator: 0602B
Ottawa, ON K1A 0K9
Tel: (613) 954-5169
Fax: (613) 957-2842
To promote and protect the health of Canadians through leadership, partnership, innovation and action in public health.
Public Health Agency of Canada