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HIV/AIDS in Vancouver, British Columbia: a growing epidemic McInnes, Colin W; Druyts, Eric; Harvard, Stephanie S; Gilbert, Mark; Tyndall, Mark W; Lima, Viviane D; Wood, Evan; Montaner, Julio S; Hogg, Robert S Mar 5, 2009

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ralssBioMed CentHarm Reduction JournalOpen AcceBrief reportHIV/AIDS in Vancouver, British Columbia: a growing epidemicColin W McInnes1,2, Eric Druyts1, Stephanie S Harvard1, Mark Gilbert3, Mark W Tyndall1,2, Viviane D Lima1,2, Evan Wood1,2, Julio SG Montaner1,2 and Robert S Hogg*1,4Address: 1British Columbia Centre for Excellence in HIV/AIDS, St. Paul's Hospital, 608-1081 Burrard Street, Vancouver, British Columbia, V6Z 1Y6, Canada, 2Faculty of Medicine, University of British Columbia, 3300-950 West 10th Avenue, Vancouver, British Columbia, V5Z 4E3, Canada, 3Division of STI/HIV Prevention and Control, British Columbia Centre for Disease Control, 655 West 12th Avenue, Vancouver, British Columbia, V5Z 4R4, Canada and 4Faculty of Health Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A 1S6, CanadaEmail: Colin W McInnes - mcinnes1@interchange.ubc.ca; Eric Druyts - edruyts@cfenet.ubc.ca; Stephanie S Harvard - harvards@interchange.ubc.ca; Mark Gilbert - mark.gilbert@bccdc.ca; Mark W Tyndall - mtyndall@cfenet.ubc.ca; Viviane D Lima - vlima@cfenet.ubc.ca; Evan Wood - uhri-ew@cfenet.ubc.ca; Julio SG Montaner - jmontaner@cfenet.ubc.ca; Robert S Hogg* - bobhogg@cfenet.ubc.ca* Corresponding author    AbstractThe prevalence of HIV in Vancouver, British Columbia was subject to two distinct periods of rapidincrease. The first occurred in the 1980s due to high incidence among men who have sex with men(MSM), and the second occurred in the 1990s due to high incidence among injection drug users(IDU). The purpose of this study was to estimate and model the trends in HIV prevalence inVancouver from 1980 to 2006. HIV prevalence data were entered into the UNAIDS/WHOEstimation and Projection Package (EPP) where prevalence trends were estimated by fitting anepidemiological model to the data. Epidemic curves were fit for IDU, MSM, street-based female sextrade workers (FSW), and the general population. Using EPP, these curves were then aggregatedto produce a model of Vancouver's overall HIV prevalence. Of the 505 000 people over the age of15 that reside in Vancouver, 6108 (ranging from 4979 to 7237) were living with HIV in the year2006, giving an overall prevalence of 1.21 percent (ranging from 0.99 to 1.43 percent). Thesubgroups of IDU and MSM account for the greatest proportion of HIV infections. Our modelestimates that the prevalence of HIV in Vancouver is greater than one percent, roughly 6 timeshigher than Canada's national prevalence. These results suggest that HIV infection is having arelatively large impact in Vancouver and that evidence-based prevention and harm reductionstrategies should be expanded.BackgroundIn Vancouver, British Columbia, the population sub-groups most affected by HIV have experienced differentrates of infection over the course of the epidemic. In theand in the mid-1990s a rapid increase in HIV incidencewas observed among injection drug users (IDU) andstreet-based female sex trade workers (FSW) [1,2].Although this shift in HIV trends was well documented, itPublished: 5 March 2009Harm Reduction Journal 2009, 6:5 doi:10.1186/1477-7517-6-5Received: 16 September 2008Accepted: 5 March 2009This article is available from: http://www.harmreductionjournal.com/content/6/1/5© 2009 McInnes et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Page 1 of 5(page number not for citation purposes)1980s, most HIV infections were accounted for by sexualtransmission among men who have sex with men (MSM),has not been adequately quantified or characterized in thehistorical context of the city's HIV epidemic.Harm Reduction Journal 2009, 6:5 http://www.harmreductionjournal.com/content/6/1/5Measuring longitudinal trends in the prevalence of HIV isessential to characterize the epidemic and to monitorchanges in high-risk population subgroups. As diseaseprevalence reflects both incidence and mortality rates,monitoring trends in HIV prevalence can provide insightinto the impact of events affecting HIV risk as well as sur-vival, such as increased use of injection cocaine or theintroduction of highly active antiretroviral therapy(HAART). Documenting HIV prevalence over time alsoprovides the denominator needed to calculate HIV-relatedhealth indicators within a temporal frame, such as theproportion of infected individuals receiving HAART or theproportion with co-infections.Despite the importance of measuring overall HIV preva-lence, current prevalence data in Vancouver have beenlimited to specific population subgroups and specificpoints in time. The purpose of this study was to combineestimates of HIV prevalence among population subgroupsin Vancouver in order to model the prevalence trends ofthese subgroups and Vancouver's overall population lon-gitudinally from 1980 to 2006.MethodsA literature search was conducted using medical and sci-entific databases (PubMed, Web of Science), nationalwebsites (Public Health Agency of Canada, Statistics Can-ada), and a general search engine (Google) in order toidentify all published and unpublished estimates of HIVprevalence in Vancouver among MSM, IDU, FSW, andpregnant women receiving antenatal testing (PW), a lowerrisk population subgroup and reference point for theremaining general population. Published and unpub-lished estimates of MSM, IDU, and FSW population sizeswere also extracted. All data sources of HIV prevalence andpopulation sizes are listed in Table 1. Since the HIV prev-alence among PW was used to reflect the prevalence of thelower risk, remaining population, they were assigned alarge population size. Population estimates for the city ofVancouver were taken from Statistics Canada [3]. The finalpopulation subgroup sizes were based on previously pub-lished estimates and peer-based discussions. Individualsunder 15 years of age were not included in our analyses asdata on this group are limited.The HIV prevalence input assumptions for the year 2006were based on the most recent available measures, all ofwhich were from the year 2003 or later. Vancouver's totalpopulation over the age of 15 was estimated to be 505 000[3]. The estimated sizes of the population subgroups areas follows: MSM 20 000 (15 000 – 25 000), IDU 13 500(10 000 – 15 000), FSW 1500 (1000 – 2000), PW 470 000(477 000 – 463 000). All estimates of HIV and populationsizes are presented in Table 2.All data were entered into the UNAIDS/WHO Estimationand Projection Package (EPP) [4], where prevalencetrends for each population subgroup were estimated lon-gitudinally by fitting an epidemic curve to the data foreach subgroup. EPP finds the curve of best fit by minimiz-ing the log likelihood of several parameters, such as thestart year of the epidemic and the rate of HIV transmis-sion. The epidemic curves that were modeled for popula-tion subgroups were aggregated by EPP to find the bestTable 1: Model parameters and data sources of subgroup population sizes and HIV prevalence dataKey parameters SourcesVancouverpopulation size Statistics Canada [3]MSM*population size Population surveys, capture-recapture estimates [11,19]HIV prevalence Cohort and cross-sectional surveys [20-23]IDU*population size Population surveys, capture-recapture estimates [11,24]HIV prevalence Cohort and cross-sectional surveys [1,25-29]FSW*population size Peer-based discussionsHIV prevalence Community-based studies of FSW [1,25,30]General population*†population size Remaining populationHIV prevalence Antenatal seroprevalence studies [31,32]*HIV prevalence estimates each included data from the Health Canada Inventory of HIV Prevalence Studies [33].Page 2 of 5(page number not for citation purposes)†The prevalence of pregnant women receiving antenatal testing was used to impute the estimate for the general population.MSM, men who have sex with men; IDU, injection drug users; FSW, street-based female sex trade worker.Harm Reduction Journal 2009, 6:5 http://www.harmreductionjournal.com/content/6/1/5fitting curve that models the overall trends of Vancouver'sHIV prevalence. Based on the estimated population sizes(Table 2), a low growth model, a high growth model, andan intermediate model, reflecting our best estimate, wereproduced for the overall population.FindingsTable 3 provides the estimates of the number of HIV-infected individuals from the specific population sub-groups and Vancouver's entire population for the year2006. We estimate that a total of 6108 (ranging from 4979to 7237) men and women were living with HIV in the year2006, producing an overall HIV prevalence of 1.21%(ranging from 0.99% to 1.43%). Our models estimatethat MSM and IDU subgroups contributed the greatestnumber of infections, with 3000 (ranging from 2250 to3750) and 2295 (ranging from 2040 to 2550) individuals,respectively.The EPP model depicting the prevalence of HIV from1980 to 2006 in each subgroup is shown in Figure 1. Themodel illustrates the rise in HIV prevalence among MSMin the 1980s as well as the rapid increase in prevalenceamong IDU and FSW in the 1990s. The upward trends ofthe model project the potential for moderate increases inHIV prevalence within each of these population sub-groups.Figure 2 characterizes the trend in Vancouver's overall HIVprevalence since 1980. The model depicts two rapidincreases in HIV prevalence, the first in the mid-1980s andthe second in the mid-1990s, and the upward trend of themodel projects the potential for a moderate futureincrease in Vancouver's overall HIV prevalence.DiscussionIn the year 2006, there were approximately 6108 (rangingfrom 4979 to 7237) people living in Vancouver that wereinfected with HIV. Populations of IDU and MSM contrib-uted the largest number of infections. Although HIV prev-alence was highest among FSW, due to the relatively smallsize of this subgroup, they accounted for only a small pro-portion of the total HIV infections in Vancouver. Few totalinfections were from PW, our reference point for the gen-eral population. Our overall estimate indicates that theprevalence of HIV in Vancouver was approximately 1.21%(ranging from 0.99% to 1.43%) in the year 2006 and theupward trend in our model suggests that there is potentialfor this value to increase slightly in the future.Table 2: Estimated population subgroup sizes and HIV prevalence for persons 15 years of age and older living in VancouverTransmission group Estimated population size (low and high estimates) HIV prevalence, 2006*MSM 20 000 (15 000 – 25 000) 15.0%IDU 13 500 (12 000 – 15 000) 17.0%FSW 1500 (1000 – 2000) 26.0%General population† 470 000 (477 000 – 463 000) 0.09%*Prevalence input assumptions for the year 2006 were based on the most recent available measures, all of which were from the year 2003 or later.†The prevalence of pregnant women receiving antenatal testing was used to impute the estimate for the general population.MSM, men who have sex with men; IDU, injection drug users; FSW, street-based female sex trade worker.Table 3: Estimated number of persons infected with HIV in Vancouver, 2006Variable HIV InfectedLow Estimate Middle Estimate High EstimateTransmission groupsMSM 2250 3000 3750IDU 2040 2295 2550FSW 260 390 520General population† 429 423 417Total populationMales 3585 4459 5355Females 1394 1649 1882Total infected 4979 6108 7237Overall prevalence 0.99% 1.21% 1.43%Page 3 of 5(page number not for citation purposes)†The prevalence of pregnant women receiving antenatal testing was used to impute the estimate for the general population.MSM, men who have sex with men; IDU, injection drug users; FSW, street-based female sex trade worker.Harm Reduction Journal 2009, 6:5 http://www.harmreductionjournal.com/content/6/1/5Our model successfully represents Vancouver's two docu-mented periods of rapid increase in HIV prevalence [1,2].The first rise in Vancouver's prevalence occurred in themid-1980s as a consequence of high HIV incidenceamong MSM [2]. However, the pace of this increase wasslowed in the late 1980s, largely as a result of mortalityassociated with the disease in the MSM subgroup [5]. Thesecond period of rapid increase resulted from high rates ofHIV transmission among Vancouver's IDU and FSW sub-groups during the mid-1990s, at which time the preva-lence of HIV in Vancouver approached 1%. Since thistime, our model suggests that the prevalence of HIV inVancouver has steadily increased and has the potential toincrease in the future. Recent increases in prevalence maybe attributed to increases in transmission among individ-uals with detectable HIV viral loads and increased survivalamong individuals on HAART [6-9].Vancouver's HIV epidemic remains concentrated in high-risk subgroups of MSM, IDU, and FSW, like other largeCanadian cities such as Montreal and Toronto [10]. Whatdistinguishes Vancouver's situation from these other cit-ies, however, is its relatively large population of high-riskindividuals, particularly IDU. For example, a previousstudy [11] estimated that the city of Vancouver has agreater number of IDU than Montreal and a comparablenumber to that found in Toronto, despite Vancouver hav-ing a smaller overall population size. Furthermore, Van-couver's estimated IDU population of 13 500 individualsrepresents between 11% and 18% of Canada's total IDUpopulation, which has been estimated to be between 75000 and 125 000 individuals [12]. Given the relativelylarge IDU and MSM populations in Vancouver, it is notsurprising that our model indicates Vancouver's overallHIV prevalence passed the 1% mark in the 1990s, duringwhich time rapid transmission of HIV was observedamong IDU [1]. Unfortunately, despite the expansion ofneedle exchange programs and the implementation ofVancouver's safe injection site, which have both shownthe potential to decrease HIV incidence [13-16], transmis-sion of HIV remains high within IDU populations [6], afinding that is reflected in our model of IDU. Similarly,our model suggests that since the mid-1990s the preva-lence of HIV among MSM has been increasing, a findingthat is also consistent with recent incidence data [7].As with any estimation of HIV prevalence, the validity ofour model is dependent on the validity of the datasources. Unfortunately, due to limitations in the availabil-ity of prevalence data, it was necessary to combine differ-ent types of data, which may have led to eitheroverestimates or underestimates of prevalence for any ofthe subgroups. For example, the most recent prevalencedata on MSM was derived from self-report of HIV statusand these data may underestimate prevalence. Further-more, because the HIV prevalence among high-risk sub-groups is not measured annually, our 2006 inputassumptions were based on the most recent availablemeasures, some of which were from the years 2003–2005.It is possible that these values have changed, and there isa need for updated seroprevalence data. Another limita-tion includes our inability to model the prevalence trendsof all high-risk population subgroups, such as individualswith mental health disorders, although this subgroupMiddle estimates of HIV prevalence for population subgroups in Vancouver, 1980–2006Figure 1Middle estimates of HIV prevalence for population subgroups in Vancouver, 1980–2006. *The prevalence of pregnant women receiving antenatal testing was used to impute the estimate for the general population. MSM, men who have sex with men; IDU, injection drug users; FSW, street-based female sex trade worker; PW, pregnant women receiving antenatal testing.0510152025301980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006YearFSW (n=390)IDU (n=2,295)MSM (n=3,000)General Population* (n=423)HIV prevalence among people living in Vancouver by upper, middle and lower estimates, 1980–2006Figure 2HIV prevalence among people living in Vancouver by 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006YearUpper Estimate (n=7,237)Middle Estimate (n=6,108)Lower Estimate (n=4,979)Page 4 of 5(page number not for citation purposes)could potentially overlap with the IDU subgroup. Conse-quently, the prevalence estimate for Vancouver's totalpopulation, which relied on data from pregnant womenupper, middle and lower estimates, 1980–2006.Harm Reduction Journal 2009, 6:5 http://www.harmreductionjournal.com/content/6/1/5to reflect HIV prevalence outside of the high-risk popula-tion subgroups, may be an underestimate. Finally, ourmodel relied on the UNAIDS EPP program, which is una-ble to account for all the epidemiological factors thatcould potentially affect HIV prevalence. Importantly,however, this program provides an accessible method formodeling HIV prevalence and may be useful in other set-tings.Our model indicates that the prevalence of HIV in the cityof Vancouver is approximately 6 times higher than Can-ada's national prevalence [17,18]. Further, the upwardtrend of our model suggests that there is potential forfuture increases in Vancouver's overall HIV prevalence[19-33]. These findings suggest that HIV infection is hav-ing a large impact in Vancouver and that evidence-basedprevention and harm reduction strategies, particularlythose targeted at high-risk population subgroups, shouldcontinue to be expanded and evaluated.Competing interestsThe authors declare that they have no competing interests.Authors' contributionsCWM, ED, SSH, VDL, JSGM, RSH initiated the study.CWM, ED, VDL performed the analyses. CWM, ED, SSHprepared the first draft. MG, MWT, EW, JSGM, RSHreviewed the manuscript for important intellectual con-tent. All authors approved the final manuscript for publi-cation.AcknowledgementsWe thank Karissa Johnston and Kate Shannon for their research assistance, and Svetlana Draskovic and Kelly Hsu for their administrative assistance.References1. Strathdee SA, Patrick DM, Currie S, et al.: Needle exchange is notenough: lessons from the Vancouver injection drug use.  AIDS1997, 11(8):F59-F65.2. 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