Estimates of the number of prevalent and incident Human Immunodeficiency Virus (HIV) infections in Canada, 2008.
Yang, Qiuying ; Boulos, David ; Yan, Ping 等
The Centre for Communicable Diseases and Infection Control (CCDIC)
of the Public Health Agency of Canada (PHAC) monitors the epidemiology
and trends of infectious diseases of public health importance in Canada,
including HIV/AIDS (human immunodeficiency virus/acquired
immunodeficiency syndrome). To help accomplish this, CCDIC conducts
ongoing surveillance of diagnosed cases of HIV and AIDS and presents
these national surveillance data in reports that provide a description
of persons diagnosed with HIV or AIDS in Canada. (1) However,
surveillance data do not fully reflect the magnitude of the HIV epidemic
because such data are subject to reporting delays, under-reporting and
changing patterns in HIV testing behaviours. Surveillance data also do
not include individuals who are untested and undiagnosed.
To provide a more accurate picture of the HIV epidemic, estimates
of HIV prevalence (the total number of people who are living with HIV at
a point in time) and incidence (the number of new HIV infections in a
population in a defined period of time) are required, and the
development of such estimates is a task undertaken around the world to
monitor the HIV epidemic. (2-8) Estimates of HIV prevalence are
important to help plan treatment and care services, and estimates of HIV
incidence support the development and evaluation of prevention programs.
We used surveillance data along with additional sources of
information and statistical modelling to estimate the number of
prevalent and incident HIV infections in Canada in 2008, including both
diagnosed and undiagnosed cases.
METHODS
We applied multiple methods to estimate the national number of
prevalent and incident HIV infections in Canada in 2008, including the
workbook method,6 two statistical modelling methods, (9,10) and an
iterative spreadsheet model. (11) The workbook method focused on
identifying populations that are at high risk of infection through their
risk behaviours and these populations were classified according to the
following exposure categories: men who have sex with men (MSM), people
who inject drugs (PWID), a separate category for persons with both risk
behaviours (MSM-PWID), heterosexual/endemic (non-PWID heterosexual with
origin in a country where heterosexual sex is the predominant mode of
HIV transmission and HIV prevalence is high (primarily countries in
sub-Saharan Africa and the Caribbean)), heterosexual/non-endemic
(non-PWID heterosexual who has had sexual contact with a person who is
either HIV-infected or at risk for HIV, or heterosexual contact as the
only identified risk) and other (primarily recipients of blood
transfusion or clotting factor, perinatal and occupational
transmission). (1) The number of prevalent or incident HIV infections
was calculated for each population by multiplying an estimated
prevalence or incidence rate by an estimated population size; data for
these rates and populations were obtained from the Canadian research
literature. The total estimated number of prevalent or incident
infections for a province was the sum of the estimated number in each
population. The statistical modelling methods calculated incident
infections based on a parametric formulation of duration of time between
HIV infection and the diagnosis of HIV infection; in brief, these models
backcalculated HIV incidence from HIV surveillance data on diagnosed
cases and from data on the HIV testing behaviour of these populations.
(9,10) The iterative spreadsheet model incorporated elements of workbook
and statistical modelling methods. (11) The results of these methods
were averaged to generate exposure category-specific estimated numbers
of prevalent and incident HIV infections in Ontario, Quebec, British
Columbia, Alberta, Saskatchewan and Manitoba. Over 98% of HIV and AIDS
cases in Canada are reported from these provinces. (1)
The remaining four provinces and three territories of Canada had
insufficient data to use the above methods and we derived estimates for
these provinces and territories by extrapolating from the above 6
provinces based on the respective proportions in provincial/territorial
HIV surveillance data, stratified by exposure category. These
surveillance data were obtained from the national HIV and AIDS
surveillance reporting system (1) with enhancements from two sources:
the Laboratory Enhancement Study in Ontario (12) and surveillance data
from Quebec. (13) The overall national number of prevalent or incident
HIV infections was calculated as the sum of the number across all
provinces and territories.
Estimates of the numbers of prevalent and incident HIV infections
among women and Aboriginal persons were derived from the overall
estimates using the distribution of cases by reported gender and
Aboriginal status from the national HIV and AIDS surveillance data,
stratified by province/territory.
The number of undiagnosed individuals living with HIV infection in
Canada was computed as the current number of prevalent infections (which
includes both diagnosed and undiagnosed cases) minus the number of
living diagnosed cases, for each exposure category and then summed. The
number of living diagnosed cases was calculated as the cumulative number
of diagnosed cases, adjusted for duplicates and under-reporting (using
unpublished data from provincial and national HIV surveillance systems)
and mortality (using data from Statistics Canada, provincial vital
statistics, national reports of AIDS deaths1 and Canadian cohort studies
(14-16)). We also validated these estimated proportions of HIV-infected
persons who are undiagnosed by comparing with directly measured
proportions from data in Canada's national second generation HIV
surveillance program among people who inject drugs and among gay,
bisexual and other men who have sex with men (refs. 17,18; PHAC,
unpublished data). In this program, participants are asked if they are
aware of their HIV status and a blood sample is taken to directly assess
HIV status.
[FIGURE 1 OMITTED]
Ranges of uncertainty for the national HIV estimates were developed
based on a conservative consideration of results from a variety of
modelled scenarios. This approach to uncertainty is similar to the
approach taken in other fields (e.g., information theory and artificial
intelligence) where information of varying quality is combined. It also
relates to work in public health where decisions are based on expert
judgement in addition to formal statistical inference. (19)
RESULTS
At the end of 2008, an estimated total of 65,000 (range:
54,00076,000) people in Canada were living with diagnosed or undiagnosed
HIV infection (including AIDS), a 14% increase from the 2005 estimate
(Table 1). The estimated prevalence rate in Canada in 2008 was 0.2%
(range: 0.16-0.23%). Figure 1 presents the estimated number of prevalent
HIV infections over time in Canada with associated ranges of
uncertainty.
[FIGURE 2 OMITTED]
The estimated number of new HIV infections in 2008 was 3,300
(range: 2,300-4,300) which was about the same as the estimate in 2005
(Table 2). The estimated incidence rate in Canada in 2008 was 9.9 per
100,000 population (range: 6.9-12.9 per 100,000 population). The
proportion of new infections attributed to the heterosexual/endemic
exposure category was 16% whereas approximately 2.2% of the Canadian
population were born in an HIV-endemic country. (20) Therefore, the
estimated incidence rate in 2008 among individuals from HIV-endemic
countries was 8.5 times higher than among other Canadians (72.5 per
100,000 population among people from HIV-endemic countries and 8.5 per
100,000 population among other Canadians). Figure 2 presents the
estimated number of incident HIV infections over time and Figure 3
presents this trend by exposure category.
There were an estimated 14,300 (12,200-16,400) women living with
diagnosed or undiagnosed HIV infection (including AIDS) in Canada (22%
of the national total) at the end of 2008, compared to 12,200
(10,400-14,000) estimated for 2005 (Table 1). For incidence, there were
860 (600 to 1,120) new HIV infections among women (26% of all new
infections) in 2008, very similar to the estimate of 845 (590 to 1,100)
for 2005 (26% of all new infections) (Table 2). With respect to exposure
category, a slightly lower proportion of new HIV infections among women
was attributed to the heterosexual category in 2008 compared to 2005
(71% versus 73%), whereas a slightly higher proportion was attributed to
PWID (29% in 2008 and 27% in 2005).
An estimated 5,200 (4,300 to 6,100) Aboriginal persons were living
with diagnosed or undiagnosed HIV infection (including AIDS) in Canada
in 2008, representing 8.0% of all prevalent HIV infections, compared to
4,200 (3,500 to 4,900) (7.4%) in 2005. An estimated 410 (300 to 520) new
HIV infections occurred in Aboriginal persons in 2008 (12.5% of all new
infections) and the corresponding figure for 2005 was 335 (240 to 430)
(10.5%). Since Aboriginal persons represent 3.8% of the Canadian
population,21 the HIV incidence rate among Aboriginal persons was about
3.6 times higher than among non-Aboriginal persons in 2008 (32.6 per
100,000 for Aboriginal population and 9.0 per 100,000 for non-Aboriginal
population). The proportion of new infections in Aboriginal persons
attributed to PWID was 66% in 2008 and 63% in 2005.
[FIGURE 3 OMITTED]
There have been 67,442 positive HIV tests reported to CCDIC from
November 1985, when testing began, to December 2008, (1) which
translates to about 70,400 after adjusting for under-reporting and
duplicates. Of these, we further estimated that approximately 22,300
have died. Thus, there were an estimated 48,100 Canadians living with
HIV infection in 2008 who were aware of their HIV-infected status. Since
there was an estimated total of 65,000 persons living with diagnosed or
undiagnosed HIV infection (including AIDS) in Canada in 2008, the
remaining 16,900 (range of 12,800-21,000) persons, or 26% of prevalent
infections, were unaware of their HIV infection. This figure was
slightly less than the estimate of 27% in 2005. The estimated proportion
of persons unaware of their HIV infection varied by exposure category
(19% in MSM, 25% in PWID, and 35% in the two combined heterosexual
exposure categories).
DISCUSSION
Approximately 65,000 Canadians were estimated to be living with
diagnosed or undiagnosed HIV infection (including AIDS) at the end of
2008. This number will increase as new infections continue and survival
improves due to new treatments, which will mean increased future care
requirements. The estimated number of new infections occurring in Canada
in 2008 was about the same as the estimated number for 2005; overall HIV
incidence is not decreasing in Canada.
Estimated HIV incidence among the PWID exposure category in Canada
in 2008 was slightly higher compared to the 2005 estimates. However, the
HIV epidemic in this group shows different trends in different
jurisdictions in Canada. In the majority of jurisdictions, the trend in
reported newly diagnosed cases of HIV infection in PWID was stable or
declining, (1) which is consistent with the trend in most high-income
countries. The role of injecting drug use in national epidemics in
Europe and the United States has declined over the past decade. (22) In
contrast, injecting drug use was the main HIV exposure category among
Aboriginal persons in Canada, and the overlap group of persons who both
were Aboriginal and inject drugs accounted for the majority of the
increasing number of new diagnoses of HIV infection reported in the
province of Saskatchewan in recent years. (1) We found that HIV
incidence among MSM in Canada increased from 1999 to 2005, but levelled
off from 2005 to 2008. The re-emergence of the epidemic among MSM is
clearly apparent in many high-income countries from 2000 to 2005.
(22-24) Heterosexual HIV transmission (combined heterosexual/non-endemic
and heterosexual/endemic categories) accounted for 36% of new infections
in Canada in 2008, which is similar to the rate in Western Europe (29%)
(22) and to the epidemic in the United States (slightly more than one
third of new HIV infections). (2,22)
Despite widespread availability of anti-retroviral treatment and
extensive promotion of HIV testing, an estimated 26% of HIV infections
remained undiagnosed in Canada in 2008. This situation is similar to
that in other high-income countries. For example, the proportion of
HIV-infected persons who were undiagnosed was estimated to be 21% in the
USA in 2006, (2) 30% in the EU in 2008, (25) and 27% in the UK in 2008.
(26) We estimated that 19% of people living with HIV among MSM in Canada
were unaware of their HIV-infected status, which is comparable with a
recent report (20%) from Australia, (27) slightly lower than the rates
estimated in the US (23.5%) (28) and the UK (26.9%), (26) and much lower
than the rate from a survey in Scotland (41.7%). (29) We estimated that
25% of people living with HIV among those who inject drugs in Canada
were unaware of their HIV status, which is similar to recent estimates
in the UK (25.5%), (26) but higher than estimates in the US (14.5% of
male PWID and 13.7% of female PWID). (28) We estimated that 35% of
people living with HIV in the heterosexual exposure category in Canada
were unaware of their serostatus, which is slightly higher than the
rates estimated in the UK (27.1%) (26) and the US (26.7% of men and
21.1% of women). (28) The size of the undiagnosed group is difficult to
estimate because without testing, its members are "hidden" to
the health care and disease monitoring systems. It is important to reach
this group since undiagnosed individuals are unable to benefit from
available treatments or appropriate counselling to prevent the further
spread of HIV. The transmission rate of HIV from undiagnosed persons is
likely higher than from tested and diagnosed persons, (30) and studies
have found that the frequency of high-risk sexual behaviour was reduced
substantially after HIV diagnosis. (31) Stemming the HIV/AIDS epidemic
requires increasing the number and proportion of people living with HIV
who are tested and informed of their serostatus. (30)
The HIV estimation process in Canada used a combination of methods
and included data from a wide variety of sources. However, the data
available were not always sufficient for the methods to estimate
exposure category-specific numbers. Several other limitations need to be
acknowledged. Estimates for the Aboriginal subpopulation relied on
ethnic variables in the HIV and AIDS surveillance data that were not
consistently reported at the national level. Exposure category
information in surveillance data was also incomplete and this may have
led to the misclassification of some cases. Furthermore, insufficient
information was available to distinguish infections acquired outside
Canada from those acquired within. These national estimates do not
necessarily reflect local trends in HIV prevalence and incidence. For
example, we found that new HIV diagnoses among the PWID exposure
category were stable or declining in the majority of jurisdictions,
while there was a substantial increase in recent years in the province
of Saskatchewan. (1) The estimates were not stratified by age because of
insufficient data. Despite these limitations, these evidence-based
estimates of prevalent and incident HIV infections portray a plausible
picture of the epidemic in Canada in 2008 and provide a robust
foundation to further the development of HIV/AIDS policies and programs.
Aboriginal people and people from HIV-endemic countries continue to
be over-represented in Canada's HIV epidemic. These findings
highlight the need for specific measures to address the unique aspects
of the HIV epidemic within certain subpopulations. To successfully
control the HIV epidemic in Canada, more effective strategies deployed
on an appropriate scale are needed to prevent new infections and provide
services for all key populations. In addition, the availability of
high-quality data is essential for developing reliable estimates to
better understand and monitor the full scope of the HIV epidemic in
Canada.
Acknowledgements: The authors acknowledge the contribution of
provincial public health officials, HIV researchers and community
representatives for their support and collaboration in producing these
estimates. We thank the provincial and territorial HIV/AIDS
coordinators, laboratories, health care providers, and reporting
physicians for providing HIV and AIDS surveillance data. The authors are
grateful to Susanna Ogunnaike-Cooke, Kristina Lalonde, Marissa McGuire
and Jill Tarasuk of CCDIC, PHAC, for providing data in support of the
estimates. In addition, we thank Jessica Halverson of CCDIC, PHAC, for
providing constructive comments on the draft manuscript.
Received: March 2, 2010 Accepted: June 28, 2010
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Qiuying Yang, MD, PhD, [1] David Boulos, MSc, [1] Ping Yan, PhD,
[1] Fan Zhang, PhD, [1] Robert S. Remis, MD, MPH, FRCPC, [2] Dena
Schanzer, MSc, [1] Chris P. Archibald, MDCM, FRCPC [1]
Author Affiliations
[1.] Centre for Communicable Diseases and Infection Control, Public
Health Agency of Canada, Ottawa, ON
[2.] Dalla Lana School of Public Health, University of Toronto,
Toronto, ON Correspondence: Dr. Chris P. Archibald, Director,
Surveillance and Risk Assessment Division, Centre for Communicable
Disease and Infection Control, Public Health Agency of Canada, 100
Eglantine Driveway, Tunney's Pasture, Ottawa, ON K1A 0K9, Tel:
613-941-3155, Fax: 613-946-8695, E-mail: chris.archibald@phac-aspc.gc.ca
Conflict of Interest: None to declare.
Table 1. Estimated Number of Prevalent HIV Infections and Associated
Ranges of Uncertainty in Canada at the End of 2008 and 2005 by
Exposure Category, Sex and Ethnicity (Point Estimates, Ranges
and Percentages Are Rounded)
Classification 2008
Point Range Percentage
Exposure category *
MSM 31,330 25,400-37,200 48%
MSM-PWID 2030 1400-2700 3%
PWID 11,180 9000-13,400 17%
Heterosexual/non-endemic 10,710 8300-13,100 17%
Heterosexual/endemic 9250 6800-11,700 14%
Others Sex 500 300-700 1%
Female 14,300 12,200-16,400 22%
Male 50,700 41,800-59,600 78%
Ethnicity
Aboriginal 5200 4300-6100 8.0%
Non-Aboriginal 59,800 49,700-69,900 92.0%
Total 65,000 54,000-76,000 100%
Classification 2005
Point Range Percentage
Exposure category *
MSM 27,700 22,400-33,000 48%
MSM-PWID 1820 1200-2400 3%
PWID 10,100 8100-12,100 18%
Heterosexual/non-endemic 9050 7000-11,100 16%
Heterosexual/endemic 7860 5800-9900 14%
Others Sex 470 280-660 1%
Female 12,200 10,400-14,000 22%
Male 44,800 36,600-53,000 78%
Ethnicity
Aboriginal 4200 3500-4900 7.4%
Non-Aboriginal 52,800 43,500-62,100 92.6%
Total 57,000 47,000-67,000 100%
* MSM: men who have sex with men; MSM-PWID: men who have sex with
men and inject drugs; PWID: people who inject drugs; Heterosexual/
non-endemic: heterosexual contact with a person who is either
HIV-infected or at risk for HIV or heterosexual contact as the
only identified risk; Heterosexual/endemic: origin in a country
where HIV is endemic; Other: recipients of blood transfusion
or clotting factor, perinatal and occupational transmission.
Table 2. Estimated Number of Incident HIV Infections and Associated
Ranges of Uncertainty in Canada in 2008 and 2005 by Exposure Category,
Sex and Ethnicity (Point Estimates, Ranges and Percentages Are Rounded)
Classification 2008
Point Range Percentage
Exposure category *
MSM 1450 1000-1900 44%
MSM-PWID 90 50-130 3%
PWID 570 390-750 17%
Heterosexual/non-endemic 655 450-860 20%
Heterosexual/endemic 530 370-690 16%
Others <20
Sex
Female 860 600-1120 26%
Male 2440 1700-3180 74%
Ethnicity
Aboriginal 410 300-520 12.5%
Non-Aboriginal 2890 2000-3780 87.5%
Total 3300 2300-4300 100%
Classification 2005
Point Range Percentage
Exposure category *
MSM 1450 1000-1900 45%
MSM-PWID 85 40-130 3%
PWID 520 360-680 16%
Heterosexual/non-endemic 630 440-820 20%
Heterosexual/endemic 515 360-670 16%
Others <20
Sex
Female 845 590-1100 26%
Male 2355 1610-3100 74%
Ethnicity
Aboriginal 335 240-430 10.5%
Non-Aboriginal 2865 1960-3770 89.5%
Total 3200 2200-4200 100%
* See footnote to Table 1
